Organic photodiodes: device engineering and applications

Abstract

Organic photodiodes (OPDs) have shown great promise for potential applications in optical imaging, sensing, and communication due to their wide-range tunable photoelectrical properties, low-temperature facile processes, and excellent mechanical flexibility. Extensive research work has been carried out on exploring materials, device structures, physical mechanisms, and processing approaches to improve the performance of OPDs to the level of their inorganic counterparts. In addition, various system prototypes have been built based on the exhibited and attractive features of OPDs. It is vital to link the device optimal design and engineering to the system requirements and examine the existing deficiencies of OPDs towards practical applications, so this review starts from discussions on the required key performance metrics for different envisioned applications. Then the fundamentals of the OPD device structures and operation mechanisms are briefly introduced, and the latest development of OPDs for improving the key performance merits is reviewed. Finally, the trials of OPDs for various applications including wearable medical diagnostics, optical imagers, spectrometers, and light communications are reviewed, and both the promises and challenges are revealed.

Graphical abstract

Keywords

Organic photodiodes / Wearable electronics / Photoplethysmography / Optical imagers / Spectrometers / Optical communications

1 Introduction

Vanadium dioxide (VO₂) is a typical thermochromic material, which has attracted extensive attention all over the world owing to its promising prospects in the fields of energy saving and emission reduction [1–3]. Though various types of VO₂ polymorphs have been developed, only the revisable crystallographic transformation between monoclinic VO₂(M) and tetragonal rutile VO₂(R) phases shows a 4–5 orders of magnitude change in resistivity and infrared transmittance at the critical transition temperature T_c of 68°C [4]. This unique metal–insulator transition (MIT) performance allows the material to be used as a switch to automatically control infrared (IR) transmission to regulate room temperature depending on the outer temperature; therefore, VO₂(M/R) is an ideal material for developing thermochromic smart windows [5].

During past decades, various types of technologies have been used to prepare high-purity VO₂(M/R). Among them, most methods in previous reports have mainly focused on the direct preparation of VO₂(M) film [6–8]. However, the process of synthesizing VO₂(M) nanoparticles first followed by the preparation of film using the as-obtained VO₂(M) nanoparticles is an equally important approach, but it has received less attention. Despite the comparatively complicated technical process, it can considerably decrease stress, which originates from the phase transition, to enhance lifespan. In addition, VO₂(M) nanoparticles can be mixed with other appropriate flexible organics to prepare VO₂(M) films with better optical performance under some specific conditions such as substrates with large area and special shapes [5]. Hence, it is still urgent and desirable to develop technology for the preparation of VO₂(M) nanoparticles.

Owing to the considerable efforts by numerous researchers, VO₂(M/R) nanoparticles have been successfully prepared by different methods such as wet chemistry [9], molten salt synthesis [10], pyrolysis [11], confined-space combustion [12], and hydrothermal synthesis [13–15]. Among them, hydrothermal synthesis is mostly used owing to its simplicity, comparatively environmentally friendly reaction conditions, and ability to control the grain growth.

Usually, the preparation of VO₂(M/R) nanoparticles through the hydrothermal synthesis process is separated into two steps: hydrothermal reaction and annealing treatment. In general, during the hydrothermal process, VO₂(B) nanobelts are generated as the mesophase and are ultimately transformed into VO₂(M/R) during the subsequent annealing treatment. Then, the primitive nanostructures of VO₂(B) are nearly destroyed [16–18]. Nevertheless, one-step hydrothermal synthesis of VO₂(M/R), without annealing treatment, provides a possibility to prepare VO₂(M) nanoparticles by controlling morphology. Though various shapes for VO₂(M) nanoparticles have been presented in previous reports (e.g., nanorods [19], star-shaped nanoparticles [20], nanorings [21,22], nanoflowers [23], nanobeams [24], hollow spheres [25], and other shapes [26,27]), the shape-controlling mechanism still remains unclear, and there are only few reports that discuss it [28].

Herein, we reported a facile process through one-step hydrothermal synthesis to prepare high-purity VO₂(M/R) nanoparticles with various types of morphologies (e.g., nanorods, nanogranules, nanoblocks, and nanospheres) that can be well-regulated by different contents of W dopants implanted in VO₂ unit cells. In addition, we proposed a detailed possible explanation for the underlying shape regulation mechanism.

2 Experimental

2.1 Materials and characterization methods

All chemical agents (analytical grade purity) were obtained from J&K Scientific, Beijing and directly used as-received without further purification. Vanadium pentoxide (V₂O₅) served as the source of V atoms. Oxalic acid (C₂H₂O₄·2H₂O) was used as the reductant. Ammonium (meta) tungstate hydrate, (NH₄)₅H₅[H₂(WO₄)₆], was used as the source of W atoms. Ethyl alcohol (C₂H₅OH) and deionized water were used as solvents for the hydrothermal reaction.

The crystalline structure was characterized by X-ray diffraction (XRD) performed on a D8 discover (Bruker, USA) instrument with the Cu Kα radiation at a 40-kV accelerating voltage and 40-mA current. The size and morphology of nanoparticles were evaluated by field emission scanning microscopy (FESEM, JEOL, Japan). The elemental composition of samples was determined by an energy-dispersive X-ray spectroscopy (EDS) instrument coupled to FESEM. The chemical bonds of the samples were analyzed to confirm the oxidation state of vanadium using X-ray photoelectron spectroscopy (XPS, ESCALab250Xi, Thermo Fisher Scientific, UK).

2.2 One-step hydrothermal synthesis of VO₂(M/R) nanoparticles

Fig.1 Schematic diagram of the one-step hydrothermal synthesis of VO2 nanoparticles

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Figure 1 shows the schematic diagram of the one-step hydrothermal synthesis of VO₂ nanoparticles. In our experiment, 0.9455 g of H₂C₂O₄ was first dispersed into 37.5 mL of deionized water under magnetic stirring in a constant-temperature bath. After complete dissolution in 5 min, 0.6825 g of V₂O₅ powder was gradually added into the reaction solution to form a brick-red suspension, which could be uniformly dispersed in another 5 min. Subsequently, we used various contents of the (NH₄)₅H₅[H₂(WO₄)₆] powder for each group (see Table 1) to add into the mixed solution under vigorous stirring conditions. In the next 30 min, the suspended particles in the mixed solution were completely dissolved. Meanwhile, the suspension color became dark blue, which was the final precursor solution. Then, the precursor solution was carefully transferred into a 50-mL Teflon-lined reaction kettle with a stainless-steel shell. Then, the reaction kettle was heated at the temperature of 280°C for 24 h with a heating rate of 8°C/min, followed by natural furnace cooling until room temperature. Next, a dark blue precipitate was observed at the bottom of the kettle and separated from the solution by vacuum filtration. Subsequently, the precipitate was sequentially washed three times with deionized water, anhydrous alcohol, and deionized water. Finally, dark blue nanoparticles were obtained after centrifuging at 7000 r/min for 5 min and drying under vacuum at 60°C for 8 h.

Tab.1 Contents of (NH4)5H5[H2(WO4)6] powder for different groups

W doping ratio/at%*	weight/g
0	0
1.0	0.03758
2.0	0.07589
3.0	0.11274
4.0	0.15178

Note: * W doping ratio refers to the atomic percent of Watoms in the total of Wand V atoms in VO2 crystals

3 Discussion

3.1 Doping efficiency of W atoms

In this section, we list the samples prepared with the W doping ratio of 1.0 at% as the value with the minimum W doping content set in our experiments. If W dopants are successfully demonstrated to be implanted into the end products for this group, it can also be applicable to other groups with a larger ratio because higher concentration indicates a stronger reaction rate.

Fig.2 Element mapping and surface spectrogram of VO2 nanoparticles prepared with the W doping ratio of 1.0 at%. (a) SEM images of nanoparticles. (b) Overall diagram of the key elements: yellow color for W element, red color for O element, and green color for V element. (c) W element. (d) O element. (e) V element. (f) Surface spectrogram of different elements in the range of 0–8 keV. Here, cps is counts per second

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Figures 2(a)–2(e) show EDS elemental mapping for the distribution of key elements in the prepared nanoparticles. It is determined that W dopants are uniformly distributed on the evaluated surface. Figure 2(f) shows the surface spectrogram in the range of 0–8 keV for VO₂ nanoparticles with the W doping ratio of 1.0 at% obtained by EDS coupled to FESEM. In addition to V and O elements, peaks for the W element are also detected at approximately 1.9, 2.1, and 8.4 keV, which confirm that W element has been successfully implanted into the final hydrothermal products.

Tab.2 Atomic percent of key elements in VO2 nanoparticles determined by EDS

nominal W doping ratio/at%*	actual W doping ratio/at%*	elements	atom%	doping efficiency/%
0	0	O V W	64.33 35.67 0	0
1.0	0.91	O V W	66.74 32.96 0.30	91.0
2.0	1.47	O V W	63.82 35.65 0.53	73.5
3.0	2.16	O V W	65.36 33.89 0.75	72.0
4.0	2.72	O V W	64.74 34.30 0.96	68.0

Note: * Nominal W doping ratio refers to the atomic ratio of W atoms in the total of W and V atoms added to the mixture solution; actual W doping ratio refers to the atomic ratio of W atoms in the total of W and V atoms in the final products.

Fig.3 Comparison of the nominal W and actual W doping content

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Table 2 shows the difference between the nominal and W doping ratios. Table 2 shows that the real content of W in the final product is always lower than their corresponding theoretical values. In addition, the doping efficiency (ratio of the actual to nominal W doping ratios) is always less than 1, which also decreases with an increase in the W doping ratio (see Fig. 3). This occurs because the starting materials in hydrothermal reaction have their own different diffusion speeds. Consequently, there is always a portion of W element that is not capable of participating in the reaction. Even if the doping efficiency in our experiment is slightly lower than that in the previous research [29], VO₂ nanorods exhibit superior doping efficiency. However, such doping efficiency in our experiment is acceptable because our reaction time is only third compared to that in the abovementioned study. In the following section, to be convenient for the readers, we still use the data of nominal W doping ratio as the W doping ratio in this study.

3.2 Mechanism of phase evolution

During the hydrothermal synthesis of VO₂(M/R) with W dopants, the possible reaction can be characterized as follows. First, V₂O₅ particles are dispersed in oxidic acid, and V⁵⁺ is reduced to V⁴⁺. The formula is shown in Eq. (1).

(1)${{\displaystyle \mathrm{V}}}_{\mathrm{2}}{{\displaystyle \mathrm{O}}}_{\mathrm{5}}+{{\displaystyle \mathrm{H}}}_{\mathrm{2}}{{\displaystyle \mathrm{C}}}_{\mathrm{2}}{{\displaystyle \mathrm{O}}}_{\mathrm{4}}\to {{\displaystyle \mathrm{V}\mathrm{O}\mathrm{C}}}_{\mathrm{2}}{{\displaystyle \mathrm{O}}}_{\mathrm{4}}+{{\displaystyle \mathrm{H}}}_{\mathrm{2}}\mathrm{O}$

In the precursor solution, ${{\displaystyle \mathrm{V}\mathrm{O}\mathrm{C}}}_{\mathrm{2}}{{\displaystyle \mathrm{O}}}_{\mathrm{4}}$ is a labile substance, which can be easily resolved into V⁴⁺. Then, V⁴⁺ ions can further form the stabilized octahedral structure of the growth unit of [VO₆]. Then, [VO₆] continues to develop into the new crystal nucleus at high temperature, which can grow into one-dimensional VO₂(B) for the following step. However, as an intermediate phase in the hydrothermal process, VO₂(B) is easily transformed into VO₂(M/R) at high temperature. Based on Leroux’s research [30], the octahedral structure of [VO₆] will be destroyed at first, and the connection between adjacent units of [VO₆] will be also broken. Then, the obtained micro molecules regrow by elongating in two directions. Thus, the metaphase of VO₂(B) is transformed into VO₂(M). During the entire process, high temperature (generally, above 280°C) is necessary for the entire phase transition to obtain pure VO₂(M) [29].

W dopants are usually added to control the phase transition temperature between VO₂(M) and VO₂(R). In recent years, numerous studies have demonstrated that W dopants can not only regulate the morphology and size of as-obtained VO₂ nanoparticles but also facilitate the phase transition from VO₂(B) to VO₂(M). A possible explanation for the mechanism is that W⁶⁺ can replace V⁴⁺ in the unit cells of VO₂(B), which leads to lattice distortion owing to the larger ionic radius of W⁶⁺ (60 pm) compared to that of V⁴⁺ (58 pm). As a result, the connection between the adjacent units of [VO₆] will break faster, giving rise to the rapid formation of VO₂(M/R). This observation provides a feasible method for the regulation of morphology, size, and purity of VO₂(M) by changing the content of W dopants added in the hydrothermal reaction. In our experiments, the source of W⁶⁺ is provided by ammonium metatungstate, which can be easily dissolved in water to generate W⁶⁺, as shown in Eq. (2).

(2)${{\displaystyle \left({{\displaystyle \mathrm{N}\mathrm{H}}}_{\mathrm{4}}\right)}}_{\mathrm{5}}{{\displaystyle \mathrm{H}}}_{\mathrm{5}}\left[{{\displaystyle \mathrm{H}}}_{\mathrm{2}}{{\displaystyle \left({{\displaystyle \mathrm{W}\mathrm{O}}}_{\mathrm{4}}\right)}}_{\mathrm{6}}\right]\to {{\displaystyle \mathrm{N}\mathrm{H}}}_{\mathrm{3}}+{{\displaystyle \mathrm{H}}}_{\mathrm{2}}\mathrm{O}+{{\displaystyle \mathrm{H}}}_{\mathrm{2}}{{\displaystyle \mathrm{W}\mathrm{O}}}_{\mathrm{4}}$

3.3 Phase behavior

Figure 4 shows XRD patterns of the hydrothermal reaction products prepared at 280°C for 24 h with different W doping ratios. For undoped VO₂, the phase of the end product is comprised of VO₂(B) and VO₂(M), which indicates that pure VO₂(M) cannot be obtained without W dopants in our experiments. However, when the W doping ratio increases to 1.0 at%, the end products are VO₂(M) nanoparticles with high purity because nearly all diffraction peaks are consistent with those of a standard VO₂(M) (JCPDS#43-1051) phase. When the W doping ratio is 2.0 at%, the end products are still pure VO₂(M) nanoparticles. Moreover, the intensity of peaks is also intensified compared to that of 1.0 at% doping ratio, which demonstrates a much higher crystallinity for the VO₂(M) crystal structure. Whereas, when the W doping ratio reaches 3.0 at%, the M(130) peak between 64° and 66° is split into R(310) and R(002) peaks (see Fig. 4), which is regarded as a diagnostic criterion for the phase transition from VO₂(M) to VO₂(R). It can be confirmed that the end product is a mixture of VO₂(M/R). However, minor impure peaks still appear at 29° despite of high purity of VO₂(M/R) nanoparticles. After the W doping ratio reaches 4.0 at%, except for the more obvious impure peaks, new impure peaks also appear at approximately 55°, which indicates that the purity of prepared VO₂(M/R) decreases. Overall, in our experiment, a certain amount of W dopants can facilitate the formation of VO₂(M) compared to nanoparticles prepared with the W doping ratio of 0, 1.0, and 2.0 at%. It can also promote the formation of VO₂(R) at the W doping ratio of 3.0 at%. However, excess amount of W dopants (4.0 at%) will lead to the generation of undesirable peaks during the hydrothermal reaction.

Fig.4 XRD patterns of prepared nanoparticles with different W doping ratios (left) and a magnified view (right) of the XRD data in the range of 64°<2θ<66°

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3.4 Morphological behavior

For undoped samples (see Fig. 5), the morphology of end products comprises hexagon nanoparticles with an average side length of 1.5 mm, aggregation bulk of multiple nanorods with an average length of 4 mm, and some snowflake nanoparticles (see Fig. 5(b)), which are mainly caused by the preferable growth of the M(011) crystal facet. Combined with the analysis of XRD patterns in Fig. 4, there still exists a portion of VO₂(B) nanobelts, which has not been transformed into VO₂(M) nanoparticles without W dopants at 280°C for 24 h.

Fig.5 SEM images of the prepared nanoparticles without W dopants. (a) Hexagon nanoparticles and nanorods. (b) Snowflake nanoparticles

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Figure 6 shows the morphology of nanoparticles prepared with the W doping ratio of 1.0 at%. The end products are a mixture of VO₂(M) nanogranules with an average diameter of 200 nm and VO₂(M) nanorods with an average length of 1 mm. Compared to undoped nanoparticles, the change in both phase and morphology is attributed to the replacement of a portion of V⁴⁺ in the VO₂ unit cell by W⁶⁺. This change accelerates the decomposition of VO₂(B) owing to aggravated lattice distortion. Furthermore, the addition of W⁶⁺ brings extra electrons, which exist in d_II orbitals and can be transferred to adjacent V⁴⁺. Thus, new chemical pairs of V³⁺–W⁶⁺ and V³⁺–V⁴⁺ are generated, which results in the formation of new oxygen vacancies of the unit cells. Consequently, the ability to incorporate surrounding elements is intensified, and the preferable growth of the M(011) peak is accelerated to generate nanorods with small size, which is confirmed by Fig. 4, where the M(011) peak becomes sharper when the W doping ratio changes from 0 to 3.0 at%.

Fig.6 SEM images of prepared nanoparticles with the W doping ratio of 1.0 at% under different magnification. (a) ×5k. (b) ×20k

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Fig.7 XPS spectrum of nanoparticles prepared with the W doping ratio of 1.0 at%. (a) General patterns. (b) V element. (c) W element. (d) O element

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To further confirm our explanation, we conducted XPS analysis of nanoparticles prepared with the W doping ratio of 1.0 at%, as shown in Fig. 7. Figure 7(a) shows the general patterns of the XPS spectrum, in which the peaks at 515–525 eV are attributed to V_2p, peaks at 35–42 eV are associated with W_4f, peak at 529.6 eV is associated with O_1s, peak at 631.5 eV is associated with V_2s, peak at 71.5 eV is associated with V_3s, and peaks at 43.2 eV and 700.0–850.5 eV are associated with V_3p and V (Auger), respectively. In addition, the peak at 516.5 eV is associated with V_2p3/2 (see Fig. 7(b)), which is below the reference value (517 eV) given for pure polycrystalline fully oxidized V₂O₅ [31] and demonstrates the existence of vanadium in low oxidation states (mainly V⁴⁺). However, this value is higher than that of pure VO₂ in previous reports [32–36], which indicates that part of V⁴⁺ is reduced into V³⁺ during the exchange reaction [37]. In Fig. 7(c), the peaks at 35.6 eV and 37.6 eV are associated with W_4f7/2 and W_4f5/2, respectively, which demonstrates the existence of W⁶⁺ in VO₂ crystal cells. Therefore, our explanation for the regulation mechanism of W⁶⁺ is further confirmed. When the W doping ratio is 2.0 at%, nanoparticles completely disappear (see Fig. 8). Instead, only nanorods are present with an average length of 3 mm. More W⁶⁺ are implanted into VO₂ unit cells when more W⁶⁺ are added into the hydrothermal solution, which induces the generation of larger crystalline grains and accelerates the growth of VO₂(M).

Fig.8 SEM images of nanoparticles prepared with the W doping ratio of 2.0 at% under different magnification. (a) ×5k. (b) ×10k

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Fig.9 SEM images of nanoparticles prepared with the W doping ratio of 3.0 at% under different magnification. (a) ×5k. (b) ×30k

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Fig.10 SEM images of nanoparticles prepared with the W doping ratio of 4.0 at% under different magnification. (a) ×5k. (b) ×15k

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Figure 9 shows nanoparticles prepared with the W doping ratio of 3.0 at%. Except for a portion of nanorods, most of them grew into massive nanoblocks with an average length of 700 nm. This result indicates that excess W⁶⁺, which was implanted into VO₂ crystal cells, promotes lattice distortion and restrains the preferable growth of the M(001) crystal facet. This conclusion is further confirmed by the wider M(001) peaks in Fig. 4. Thus, massive nanoparticles with square and spherical shapes are generated. When the W doping ratio is increased to 4.0 at%, nanospheres are formed with an average diameter of 2 mm; these spheres are made of many nanoparticles with rough surfaces, as shown in Fig. 10. The lattice distortion of VO₂ crystal cells owing to the implantation of W⁶⁺ is further promoted, and the preferable growth of M(001) crystal facet is further restrained. Impure crystals are also observed in the end products.

Fig.11 Overall schematic diagram of evolution of VO2 nanoparticles and regulation scheme

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Finally, the overall schematic diagram of the evolution of VO₂ nanoparticles and the regulation scheme based on different W doping contents is shown in Fig. 11. The morphologies of nanoparticles prepared in our experiment varied from nanogranules, nanorods, nanoblocks to nanospheres with an increase in the W doping content from 0 to 4.0 at%. In addition, we confirmed that W dopants can promote the phase transformation from VO₂(B) to VO₂(M), and the average size of as-obtained nanoparticles is increased from 200 nm to 2 mm with an increase in the W doping content.

4 Conclusions

In summary, we prepared high-purity VO₂(M/R) nanoparticles with various types of morphologies (e.g., nanogranules, nanorods, nanoblocks, and nanospheres) through one-step hydrothermal synthesis that is based on different W doping content. In our experiments, W dopants are essential in regulating the morphology of VO₂(M/R) nanoparticles through restraining the preferable growth of VO₂(M/R). In addition, we confirmed that a certain number of W dopants can promote the phase transformation from VO₂(B) to VO₂(M/R); however, excess content can lead to the generation of undesirable crystals and lower purity of nanoparticles. In general, our study provides a facile process by combining hydrothermal synthesis with W doping strategies to prepare high-purity shape-controlled VO₂(M/R) nanoparticles. This process is expected to be used in industrial mass production in the field of thermochromic smart windows because the process is simple, environmentally friendly, and allows to control the crystal growth. In addition, the approach used in this study to control the process of crystal growth with inorganic dopants to obtain shape-controlled nanoparticles can be also applied to the preparation of other metallic crystals to obtain desired morphologies.

References

[1] García de Arquer, F.P., Armin, A., Meredith, P., Sargent, E.H.: Solution-processed semiconductors for next-generation photo-detectors. Nat. Rev. Mater. 2(3), 1–17(2017)

[2] Tan, C.L., Mohseni, H.: Emerging technologies for high performance infrared detectors. Nanophotonics 7(1), 169–197(2018)

[3] Rogalski, A., Kopytko, M., Martyniuk, P.: 2D material infrared and terahertz detectors: status and outlook. Opto-Electron. Rev. 28(3), 107–154(2020)

[4] Saran, R., Curry, R.J.: Lead sulphide nanocrystal photodetector technologies. Nat. Photon. 10(2), 81–92(2016)

[5] Bruns, O.T., Bischof, T.S., Harris, D.K., Franke, D., Shi, Y., Riedemann, L., Bartelt, A., Jaworski, F.B., Carr, J.A., Rowlands, C.J., Wilson, M.W.B., Chen, O., Wei, H., Hwang, G.W., Montana, D.M., Coropceanu, I., Achorn, O.B., Kloepper, J., Heeren, J., So, P.T.C., Fukumura, D., Jensen, K.F., Jain, R.K., Bawendi, M.G.: Next-generation in vivo optical imaging with short-wave infrared quantum dots. Nat. Biomed. Eng. 1(4), 1–11(2017)

[6] Xu, Y., Lin, Q.: Photodetectors based on solution-processable semiconductors: recent advances and perspectives. Appl. Phys. Rev. 7(1), 011315(2020)

[7] Lau, Y.S., Lan, Z., Cai, L., Zhu, F.: High-performance solution-processed large-area transparent self-powered organic near-infrared photodetectors. Mater. Today Energy. 21, 100708(2021)

[8] Ng, T.N., Wong, W.S., Chabinyc, M.L., Sambandan, S., Street, R.A.: Flexible image sensor array with bulk heterojunction organic photodiode. Appl. Phys. Lett. 92(21), 213303(2008)

[9] Pierre, A., Deckman, I., Lechêne, P.B., Arias, A.C.: High detectivity all-printed organic photodiodes. Adv. Mater. 27(41), 6411–6417(2015)

[10] Verstraeten, F., Gielen, S., Verstappen, P., Raymakers, J., Penxten, H., Lutsen, L., Vandewal, K., Maes, W.: Efficient and readily tuneable near-infrared photodetection up to 1500 nm enabled by thiadiazoloquinoxaline-based push–pull type conjugated polymers. J. Mater. Chem. C Mater. Opt. Electron. Devices. 8(29), 10098–10103(2020)

[11] Guo, D., Yang, L., Zhao, J., Li, J., He, G., Yang, D., Wang, L., Vadim, A., Ma, D.: Visible-blind ultraviolet narrowband photomultiplication-type organic photodetector with an ultrahigh external quantum efficiency of over 1000000. Mater. Horiz. 8(8), 2293–2302(2021)

[12] Ding, N., Wu, Y., Xu, W., Lyu, J., Wang, Y., Zi, L., Shao, L., Sun, R., Wang, N., Liu, S., Zhou, D., Bai, X., Zhou, J., Song, H.: A novel approach for designing efficient broadband photodetectors expanding from deep ultraviolet to near infrared. Light Sci. Appl. 11(1), 91(2022)

[13] Jacoutot, P., Scaccabarozzi, A.D., Zhang, T., Qiao, Z., Aniés, F., Neophytou, M., Bristow, H., Kumar, R., Moser, M., Nega, A.D., Schiza, A., Dimitrakopoulou-Strauss, A., Gregoriou, V.G., Anthopoulos, T.D., Heeney, M., McCulloch, I., Bakulin, A.A., Chochos, C.L., Gasparini, N.: Infrared organic photodetectors employing ultralow bandgap polymer and non-fullerene acceptors for biometric monitoring. Small 18(15), e2200580(2022)

[14] Fuentes-Hernandez, C., Chou, W.F., Khan, T.M., Diniz, L., Lukens, J., Larrain, F.A., Rodriguez-Toro, V.A., Kippelen, B.: Large-area low-noise flexible organic photodiodes for detecting faint visible light. Science 370(6517), 698–701(2020)

[15] Park, S., Fukuda, K., Wang, M., Lee, C., Yokota, T., Jin, H., Jinno, H., Kimura, H., Zalar, P., Matsuhisa, N., Umezu, S., Bazan, G.C., Someya, T.: Ultraflexible near-infrared organic photodetectors for conformal photoplethysmogram sensors. Adv. Mater. 30(34), e1802359(2018)

[16] Chow, P.C.Y., Someya, T.: Organic photodetectors for nextgeneration wearable electronics. Adv. Mater. 32(15), e1902045(2020)

[17] Wang, C., Zhang, X., Hu, W.: Organic photodiodes and phototransistors toward infrared detection: materials, devices, and applications. Chem. Soc. Rev. 49(3), 653–670(2020)

[18] Simone, G., Dyson, M.J., Meskers, S.C.J., Janssen, R.A.J., Gelinck, G.H.: Organic photodetectors and their application in large area and flexible image sensors: the role of dark current. Adv. Funct. Mater. 30(20), 1904205(2020)

[19] Ren, H., Chen, J.D., Li, Y.Q., Tang, J.X.: Recent progress in organic photodetectors and their applications. Adv. Sci. (Weinh.) 8(1), 2002418(2021)

[20] Yokota, T., Fukuda, K., Someya, T.: Recent progress of flexible image sensors for biomedical applications. Adv. Mater. 33(19), e2004416(2021)

[21] Matheus, L.E.M., Vieira, A.B., Vieira, L.F., Vieira, M.A., Gnawali, O.: Visible light communication: concepts, applications and challenges. IEEE Comm. Surv. Tutor. 21(4), 3204–3237(2019)

[22] Lau, Y., Zhu, F.: Visualization of near-infrared light and applications. Chin. J. Liq. Crys. Disp. 36(1), 78–104(2021)

[23] Naseer, N., Hong, K.S.: fNIRS-based brain-computer interfaces: a review. Front. Hum. Neurosci. 9, 3(2015)

[24] Li, N., Eedugurala, N., Azoulay, J.D., Ng, T.N.: A filterless organic photodetector electrically switchable between visible and infrared detection. Cell Rep. Phys. Sci. 3(1), 100711(2022)

[25] Zhang, D., Fuentes-Hernandez, C., Vijayan, R., Zhang, Y., Li, Y., Park, J.W., Wang, Y., Zhao, Y., Arora, N., Mirzazadeh, A., Do, Y., Cheng, T., Swaminathan, S., Starner, T., Andrew, T.L., Abowd, G.D.: Flexible computational photodetectors for self-powered activity sensing. NPJ Flex. Electron. 6(1), 1–8(2022)

[26] Li, N., Eedugurala, N., Leem, D.S., Azoulay, J.D., Ng, T.N.: Organic upconversion imager with dual electronic and optical readouts for shortwave infrared light detection. Adv. Funct. Mater. 31(16), 2100565(2021)

[27] Li, N., Lan, Z., Lau, Y.S., Xie, J., Zhao, D., Zhu, F.: Swir photo-detection and visualization realized by incorporating an organic SWIR sensitive bulk heterojunction. Adv. Sci. (Weinh.) 7(14), 2000444(2020)

[28] Du, X., Han, J., He, Z., Han, C., Wang, X., Wang, J., Jiang, Y., Tao, S.: Efficient organic upconversion devices for low energy consumption and high-quality noninvasive imaging. Adv. Mater. 33(42), e2102812(2021)

[29] Yang, D., Zhou, X., Ma, D., Vadim, A., Ahamad, T., Alshehri, S.M.: Near infrared to visible light organic up-conversion devices with photon-to-photon conversion efficiency approaching 30%. Mater. Horiz. 5(5), 874–882(2018)

[30] Tedde, S., Zaus, E., Furst, J., Henseler, D., Lugli, P.: Active pixel concept combined with organic photodiode for imaging devices. IEEE Electron Device Lett. 28(10), 893–895(2007)

[31] Yokota, T., Nakamura, T., Kato, H., Mochizuki, M., Tada, M., Uchida, M., Lee, S., Koizumi, M., Yukita, W., Takimoto, A., Someya, T.: A conformable imager for biometric authentication and vital sign measurement. Nat. Electron. 3(2), 113–121(2020)

[32] Zhao, C., Kanicki, J.: Amorphous In-Ga-Zn-O thin-film transistor active pixel sensor X-ray imager for digital breast tomosynthesis. Med. Phys. 41(9), 091902(2014)

[33] Hou, X., Chen, S., Tang, W., Liang, J., Ouyang, B., Li, M., Song, Y., Shan, T., Chen, C.C., Too, P., Wei, X., Jin, L., Qi, G., Guo, X.: Low-temperature solution-processed all organic integration for large-area and flexible high-resolution imaging. IEEE J. Electron Devices Soc. 10, 821–826(2022)

[34] Gelinck, G.H., Kumar, A., Moet, D., van der Steen, J.L., Shafique, U., Malinowski, P.E., Myny, K., Rand, B.P., Simon, M., Rütten, W., Douglas, A., Jorritsma, J., Heremans, P., Andriessen, R.: X-ray imager using solution processed organic transistor arrays and bulk heterojunction photodiodes on thin, flexible plastic substrate. Org. Electron. 14(10), 2602–2609(2013)

[35] Xing, S., Nikolis, V.C., Kublitski, J., Guo, E., Jia, X., Wang, Y., Spoltore, D., Vandewal, K., Kleemann, H., Benduhn, J., Leo, K.: Miniaturized Vis-NIR spectrometers based on narrowband and tunable transmission cavity organic photodetectors with ultra-high specific detectivity above 1014 Jones. Adv. Mater. 33(44), e2102967(2021)

[36] Tang, Z., Ma, Z., Sánchez-Díaz, A., Ullbrich, S., Liu, Y., Siegmund, B., Mischok, A., Leo, K., Campoy-Quiles, M., Li, W., Vandewal, K.: Polymer: fullerene bimolecular crystals for near-infrared spectroscopic photodetectors. Adv. Mater. 29(33), 1702184(2017)

[37] Chow, C.W., Wang, H.Y., Chen, C.H., Zan, H.W., Yeh, C.H., Meng, H.F.: Pre-distortion scheme to enhance the transmission performance of organic photo-detector (OPD) based visible light communication (VLC). IEEE Access 6, 7625–7630(2018)

[38] Li, W., Li, S., Duan, L., Chen, H., Wang, L., Dong, G., Xu, Z.: Squarylium and rubrene based filterless narrowband photodetectors for an all-organic two-channel visible light communication system. Org. Electron. 37, 346–351(2016)

[39] Lan, Z., Lau, Y.S., Cai, L., Han, J., Suen, C.W., Zhu, F.: Dualband organic photodetectors for dual-channel optical communications. Laser Photon. Rev. 16(7), 2100602(2022)

[40] Strobel, N., Droseros, N., Köntges, W., Seiberlich, M., Pietsch, M., Schlisske, S., Lindheimer, F., Schröder, R.R., Lemmer, U., Pfannmöller, M., Banerji, N., Hernandez-Sosa, G.: Color-selective printed organic photodiodes for filterless multichannel visible light communication. Adv. Mater. 32(12), e1908258(2020)

[41] Babics, M., Bristow, H., Zhang, W., Wadsworth, A., Neophytou, M., Gasparini, N., McCulloch, I.: Non-fullerene-based organic photodetectors for infrared communication. J. Mater. Chem. C Mater. Opt. Electron. Devices 9(7), 2375–2380(2021)

[42] Lee, S.H., Yusoff, A., Lee, C., Yoon, S.C., Noh, Y.Y.: Toward color-selective printed organic photodetectors for high-resolution image sensors: from fundamentals to potential commercialization. Mater. Sci. Eng. Rep. 147, 100660(2022)

[43] Song, J.K., Kim, M.S., Yoo, S., Koo, J.H., Kim, D.H.: Materials and devices for flexible and stretchable photodetectors and light-emitting diodes. Nano Res. 14(9), 2919–2937(2021)

[44] Lan, Z., Lee, M.H., Zhu, F.: Recent advances in solution-processable organic photodetectors and applications in flexible electronics. Adv. Intell. Syst. 4(3), 2100167(2022)

[45] Li, N., Mahalingavelar, P., Vella, J.H., Leem, D.S., Azoulay, J.D., Ng, T.N.: Solution-processable infrared photodetectors: materials, device physics, and applications. Mater. Sci. Eng. Rep. 146, 100643(2021)

[46] Simone, G., Dyson, M.J., Weijtens, C.H.L., Meskers, S.C.J., Coehoorn, R., Janssen, R.A.J., Gelinck, G.H.: On the origin of dark current in organic photodiodes. Adv. Opt. Mater. 8(1), 1901568(2020)

[47] Fang, Y., Armin, A., Meredith, P., Huang, J.: Accurate characterization of next-generation thin-film photodetectors. Nat. Photon. 13(1), 1–4(2019)

[48] Lee, H., Park, C., Sin, D.H., Park, J.H., Cho, K.: Recent advances in morphology optimization for organic photovoltaics. Adv. Mater. 30(34), e1800453(2018)

[49] Gaspar, H., Figueira, F., Pereira, L., Mendes, A., Viana, J.C., Bernardo, G.: Recent developments in the optimization of the bulk heterojunction morphology of polymer: fullerene solar cells. Materials (Basel) 11(12), E2560(2018)

[50] Brabec, C.J., Durrant, J.R.: Solution-processed organic solar cells. MRS Bull. 33(7), 670–675(2008)

[51] Ma, L., Zhang, S., Wang, J., Xu, Y., Hou, J.: Recent advances in non-fullerene organic solar cells: from lab to fab. Chem. Commun. (Camb.) 56(92), 14337–14352(2020)

[52] Dou, L., Liu, Y., Hong, Z., Li, G., Yang, Y.: Low-bandgap near-IR conjugated polymers/molecules for organic electronics. Chem. Rev. 115(23), 12633–12665(2015)

[53] Pivrikas, A., Sariciftci, N.S., Juška, G., Österbacka, R.: A review of charge transport and recombination in polymer/fullerene organic solar cells. Prog. Photovolt. Res. Appl. 15(8), 677–696(2007)

[54] Ameri, T., Heumüller, T., Min, J., Li, N., Matt, G., Scherf, U., Brabec, C.J.: IR sensitization of an indene-C60 bisadduct (ICBA) in ternary organic solar cells. Energy Environ. Sci. 6(6), 1796–1801 (2013)

[55] Zhang, J., Tan, H.S., Guo, X., Facchetti, A., Yan, H.: Material insights and challenges for non-fullerene organic solar cells based on small molecular acceptors. Nat. Energy 3(9), 720–731(2018)

[56] Liu, W., Zhang, R., Wei, Q., Zhu, C., Yuan, J., Gao, F., Zou, Y.: Manipulating molecular aggregation and crystalline behavior of A-DA’D-A type acceptors by side chain engineering in organic solar cells. Aggregate 3(3), e183(2022)

[57] Zhang, X., Li, G., Mukherjee, S., Huang, W., Zheng, D., Feng, L.W., Chen, Y., Wu, J., Sangwan, V.K., Hersam, M.C., DeLongchamp, D.M., Yu, J., Facchetti, A., Marks, T.J.: Systematically controlling acceptor fluorination optimizes hierarchical morphology, vertical phase separation, and efficiency in non-fullerene organic solar cells. Adv. Energy Mater. 12(1), 2102172(2022)

[58] Wang, Z., Zhu, L., Shuai, Z., Wei, Z.: A–π–D–π–A electron-donating small molecules for solution-processed organic solar cells: a review. Macromol. Rapid Commun. 38(22), 1700470(2017)

[59] Shan, T., Ding, K., Yu, L., Wang, X., Zhang, Y., Zheng, X., Chen, C.C., Peng, Q., Zhong, H.: Spatially orthogonal 2d sidechains optimize morphology in all-small-molecule organic solar cells. Adv. Funct. Mater. 31(24), 2100750(2021)

[60] Li, Y., Chen, H., Zhang, J.: Carrier blocking layer materials and application in organic photodetectors. Nanomaterials (Basel) 11(6), 1404(2021)

[61] Lim, S.B., Ji, C.H., Oh, I.S., Oh, S.Y.: Reduced leakage current and improved performance of an organic photodetector using an ytterbium cathode interlayer. J. Mater. Chem. C Mater. Opt. Electron. Devices 4(22), 4920–4926(2016)

[62] Bouthinon, B., Clerc, R., Verilhac, J., Racine, B., De Girolamo, J., Jacob, S., Lienhard, P., Joimel, J., Dhez, O., Revaux, A.: On the front and back side quantum efficiency differences in semitransparent organic solar cells and photodiodes. J. Appl. Phys. 123(12), 125501(2018)

[63] Sato, Y., Kajii, H., Ohmori, Y.: Improved performance of polymer photodetectors using indium–tin-oxide modified by phosphonic acid-based self-assembled monolayer treatment. Org. Electron. 15(8), 1753–1758(2014)

[64] Zhou, Y., Fuentes-Hernandez, C., Shim, J., Meyer, J., Giordano, A.J., Li, H., Winget, P., Papadopoulos, T., Cheun, H., Kim, J., Fenoll, M., Dindar, A., Haske, W., Najafabadi, E., Khan, T.M., Sojoudi, H., Barlow, S., Graham, S., Brédas, J.L., Marder, S.R., Kahn, A., Kippelen, B.: A universal method to produce low-work function electrodes for organic electronics. Science 336(6079), 327–332(2012)

[65] He, Z., Zhang, C., Xu, X., Zhang, L., Huang, L., Chen, J., Wu, H., Cao, Y.: Largely enhanced efficiency with a PFN/Al bilayer cathode in high efficiency bulk heterojunction photovoltaic cells with a low bandgap polycarbazole donor. Adv. Mater. 23(27), 3086–3089(2011)

[66] Wang, T., Wang, Y., Zhu, L., Lv, L., Hu, Y., Deng, Z., Cui, Q., Lou, Z., Hou, Y., Teng, F.: High sensitivity and fast response sol-gel ZnO electrode buffer layer based organic photodetectors with large linear dynamic range at low operating voltage. Org. Electron. 56, 51–58(2018)

[67] Zhu, H.L., Choy, W.C., Sha, W.E., Ren, X.: Photovoltaic mode ultraviolet organic photodetectors with high on/off ratio and fast response. Adv. Opt. Mater. 2(11), 1082–1089(2014)

[68] Deng, R., Yan, C., Deng, Y., Hu, Y., Deng, Z., Cui, Q., Lou, Z., Hou, Y., Teng, F.: High-performance polymer photodetector using the non-thermal-and-non-ultraviolet–ozone-treated SnO₂ interfacial layer. Physica Status Solidi (RRL) - Rapid Res. Lett. 14(3), 1900531(2020)

[69] Zheng, Z., Wang, J., Bi, P., Ren, J., Wang, Y., Yang, Y., Liu, X., Zhang, S., Hou, J.: Tandem organic solar cell with 20.2% efficiency. Joule 6(1), 171–184(2022)

[70] Lu, H., Lin, J., Wu, N., Nie, S., Luo, Q., Ma, C.Q., Cui, Z.: Inkjet printed silver nanowire network as top electrode for semi-transparent organic photovoltaic devices. Appl. Phys. Lett. 106(9), 093302(2015)

[71] Baeg, K.J., Binda, M., Natali, D., Caironi, M., Noh, Y.Y.: Organic light detectors: photodiodes and phototransistors. Adv. Mater. 25(31), 4267–4295(2013)

[72] Tam, K.C., Kubis, P., Maisch, P., Brabec, C.J., Egelhaaf, H.J.: Fully printed organic solar modules with bottom and top silver nanowire electrodes. Prog. Photovolt. Res. Appl. 30(5), 528–542(2022)

[73] Cao, W., Li, J., Chen, H., Xue, J.: Transparent electrodes for organic optoelectronic devices: a review. J. Photon. Energy 4(1), 040990(2014)

[74] Kim, D.H., Kim, K.S., Shim, H.S., Moon, C.K., Jin, Y.W., Kim, J.J.: A high performance semitransparent organic photodetector with green color selectivity. Appl. Phys. Lett. 105(21), 213301(2014)

[75] Kim, H., Lee, K.T., Zhao, C., Guo, L.J., Kanicki, J.: Top illuminated organic photodetectors with dielectric/metal/dielectric transparent anode. Org. Electron. 20, 103–111(2015)

[76] Zhang, H., Jenatsch, S., De Jonghe, J., Nüesch, F., Steim, R., Véron, A.C., Hany, R.: Transparent organic photodetector using a near-infrared absorbing cyanine dye. Sci. Rep. 5(1), 9439(2015)

[77] Qi, Z., Cao, J., Ding, L., Wang, J.: Transparent and transferrable organic optoelectronic devices based on WO₃/Ag/WO₃ electrodes. Appl. Phys. Lett. 106(5), 053304(2015)

[78] Lee, D., So, S., Hu, G., Kim, M., Badloe, T., Cho, H., Kim, J., Kim, H., Qiu, C.-W., Rho, J.: Hyperbolic metamaterials: fusing artificial structures to natural 2D materials. eLight 2(1), 1–23(2022)

[79] Shan, T., Zhang, Y., Wang, Y., Xie, Z., Wei, Q., Xu, J., Zhang, M., Wang, C., Bao, Q., Wang, X., Chen, C.C., Huang, J., Chen, Q., Liu, F., Chen, L., Zhong, H.: Universal and versatile morphology engineering via hot fluorous solvent soaking for organic bulk heterojunction. Nat. Commun. 11(1), 5585(2020)

[80] Luo, D., Zhang, Y., Li, L., Shan, C., Liu, Q., Wang, Z., Choy, W.C., Kyaw, A.K.K.: Near-infrared non-fused ring acceptors with light absorption up to 1000 nm for efficient and low-energy loss organic solar cells. Mater. Today Energy 24, 100938(2022)

[81] Li, Y., Huang, W., Zhao, D., Wang, L., Jiao, Z., Huang, Q., Wang, P., Sun, M., Yuan, G.: Recent progress in organic solar cells: a review on materials from acceptor to donor. Molecules 27(6), 1800(2022)

[82] Wang, Z., Peng, Z., Xiao, Z., Seyitliyev, D., Gundogdu, K., Ding, L., Ade, H.: Thermodynamic properties and molecular packing explain performance and processing procedures of three D18:NFA organic solar cells. Adv. Mater. 32(49), e2005386(2020)

[83] Wei, Q., Yuan, J., Yi, Y., Zhang, C., Zou, Y.: Y6 and its derivatives: molecular design and physical mechanism. Natl. Sci. Rev. 8(8), nwa121(2021)

[84] Yuan, J., Zhang, Y., Zhou, L., Zhang, G., Yip, H.L., Lau, T.K., Lu, X., Zhu, C., Peng, H., Johnson, P.A., Leclerc, M., Cao, Y., Ulanski, J., Li, Y., Zou, Y.: Single-junction organic solar cell with over 15% efficiency using fused-ring acceptor with electrondeficient core. Joule 3(4), 1140–1151(2019)

[85] Park, B., Jung, J., Lim, D.H., Lee, H., Park, S., Kyeong, M., Ko, S.J., Eom, S.H., Lee, S.H., Lee, C., Yoon, S.C.: Significant dark current suppression in organic photodetectors using side chain fluorination of conjugated polymer. Adv. Funct. Mater. 32(4), 2108026(2022)

[86] Zhang, D., Zhao, D., Wang, Z., Yu, J.: Processes controlling the distribution of vertical organic composition in organic photodetectors by ultrasonic-assisted solvent vapor annealing. ACS Appl. Electron. Mater. 2(7), 2188–2195(2020)

[87] Biele, M., Montenegro Benavides, C., Hürdler, J., Tedde, S.F., Brabec, C.J., Schmidt, O.: Spray-coated organic photodetectors and image sensors with silicon-like performance. Adv. Mater. Technol. 4(1), 1800158(2019)

[88] Huang, J., Lee, J., Vollbrecht, J., Brus, V.V., Dixon, A.L., Cao, D.X., Zhu, Z., Du, Z., Wang, H., Cho, K., Bazan, G.C., Nguyen, T.Q.: A high-performance solution-processed organic photodetector for near-infrared sensing. Adv. Mater. 32(1), e1906027(2020)

[89] Xu, Y., Yuan, J., Liang, S., Chen, J.D., Xia, Y., Larson, B.W., Wang, Y., Su, G.M., Zhang, Y., Cui, C., Wang, M., Zhao, H., Ma, W.: Simultaneously improved efficiency and stability in all-polymer solar cells by a p–i–n architecture. ACS Energy Lett. 4(9), 2277–2286(2019)

[90] Shan, T., Hong, Y., Zhu, L., Wang, X., Zhang, Y., Ding, K., Liu, F., Chen, C.C., Zhong, H.: Achieving optimal bulk hetero-junction in all-polymer solar cells by sequential processing with nonorthogonal solvents. ACS Appl. Mater. Interfaces 11(45), 42438–42446(2019)

[91] Kim, M.S., Jang, W., Nguyen, T.Q., Wang, D.H.: Morphology inversion of a non-fullerene acceptor via adhesion controlled decal-coating for efficient conversion and detection in organic electronics. Adv. Funct. Mater. 31(38), 2103705(2021)

[92] Zhong, Z., Bu, L., Zhu, P., Xiao, T., Fan, B., Ying, L., Lu, G., Yu, G., Huang, F., Cao, Y.: Dark current reduction strategy via a layer-by-layer solution process for a high-performance all-polymer photodetector. ACS Appl. Mater. Interfaces 11(8), 8350–8356(2019)

[93] Sun, R., Guo, J., Sun, C., Wang, T., Luo, Z., Zhang, Z., Jiao, X., Tang, W., Yang, C., Li, Y., Min, J.: A universal layer-by-layer solution-processing approach for efficient non-fullerene organic solar cells. Energy Environ. Sci. 12(1), 384–395(2019)

[94] Wei, Y., Chen, H., Liu, T., Wang, S., Jiang, Y., Song, Y., Zhang, J., Zhang, X., Lu, G., Huang, F., Wei, Z., Huang, H.: Self-powered organic photodetectors with high detectivity for near infrared light detection enabled by dark current reduction. Adv. Funct. Mater. 31(52), 2106326(2021)

[95] Xiong, S., Li, J., Peng, J., Dong, X., Qin, F., Wang, W., Sun, L., Xu, Y., Lin, Q., Zhou, Y.: Water transfer printing of multi-layered near-infrared organic photodetectors. Adv. Opt. Mater. 10(1), 2101837(2022)

[96] Huang, Z., Zhong, Z., Peng, F., Ying, L., Yu, G., Huang, F., Cao, Y.: Copper thiocyanate as an anode interfacial layer for efficient near-infrared organic photodetector. ACS Appl. Mater. Interfaces 13(1), 1027–1034(2021)

[97] Xu, X., Zhou, X., Zhou, K., Xia, Y., Ma, W., Inganäs, O.: Largearea, semitransparent, and flexible all-polymer photodetectors. Adv. Funct. Mater. 28(48), 1805570(2018)

[98] Saracco, E., Bouthinon, B., Verilhac, J.M., Celle, C., Chevalier, N., Mariolle, D., Dhez, O., Simonato, J.P.: Work function tuning for high-performance solution-processed organic photodetectors with inverted structure. Adv. Mater. 25(45), 6534–6538(2013)

[99] Binda, M., Iacchetti, A., Natali, D., Beverina, L., Sassi, M., Sampietro, M.: High detectivity squaraine-based near infrared photodetector with NA/cm² dark current. Appl. Phys. Lett. 98(7), 073303(2011)

[100] Zhou, X., Yang, D., Ma, D.: Extremely low dark current, high responsivity, all-polymer photodetectors with spectral response from 300 nm to 1000 nm. Adv. Opt. Mater. 3(11), 1570–1576(2015)

[101] Benavides, C.M., Murto, P., Chochos, C.L., Gregoriou, V.G., Avgeropoulos, A., Xu, X., Bini, K., Sharma, A., Andersson, M.R., Schmidt, O., Brabec, C.J., Wang, E., Tedde, S.F.: High-performance organic photodetectors from a high-bandgap indacenodithiophene-based π-conjugated donor-acceptor polymer. ACS Appl. Mater. Interfaces 10(15), 12937–12946(2018)

[102] Sim, K.M., Yoon, S., Kim, S.K., Ko, H., Hassan, S.Z., Chung, D.S.: Surfactant-induced solubility control to realize water-processed high-precision patterning of polymeric semiconductors for full color organic image sensor. ACS Nano 14(1), 415–421(2020)

[103] Lan, Z., Zhu, F.: Electrically switchable color-selective organic photodetectors for full-color imaging. ACS Nano 15(8), 13674–13682(2021)

[104] Yang, J., Huang, J., Li, R., Li, H., Sun, B., Lin, Q., Wang, M., Ma, Z., Vandewal, K., Tang, Z.: Cavity-enhanced near-infrared organic photodetectors based on a conjugated polymer containing [1,2,5]selenadiazolo[3,4-c]pyridine. Chem. Mater. 33(13), 5147–5155(2021)

[105] Lan, Z., Lau, Y.S., Wang, Y., Xiao, Z., Ding, L., Luo, D., Zhu, F.: Filter-free band-selective organic photodetectors. Adv. Opt. Mater. 8(24), 2001388(2020)

[106] Vanderspikken, J., Maes, W., Vandewal, K.: Wavelength-selective organic photodetectors. Adv. Funct. Mater. 31(36), 2104060(2021)

[107] Schembri, T., Kim, J.H., Liess, A., Stepanenko, V., Stolte, M., Würthner, F.: Semitransparent layers of social self-sorting merocyanine dyes for ultranarrow bandwidth organic photodiodes. Adv. Opt. Mater. 9(15), 2100213(2021)

[108] Wang, Y., Kublitski, J., Xing, S., Dollinger, F., Spoltore, D., Benduhn, J., Leo, K.: Narrowband organic photodetectors-towards miniaturized, spectroscopic sensing. Mater. Horiz. 9(1), 220–251(2022)

[109] Armin, A., Jansen-van Vuuren, R.D., Kopidakis, N., Burn, P.L., Meredith, P.: Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes. Nat. Commun. 6(1), 6343(2015)

[110] Wang, W., Zhang, F., Du, M., Li, L., Zhang, M., Wang, K., Wang, Y., Hu, B., Fang, Y., Huang, J.: Highly narrowband photomultiplication type organic photodetectors. Nano Lett. 17(3), 1995–2002(2017)

[111] Xie, B., Xie, R., Zhang, K., Yin, Q., Hu, Z., Yu, G., Huang, F., Cao, Y.: Self-filtering narrowband high performance organic photodetectors enabled by manipulating localized Frenkel exciton dissociation. Nat. Commun. 11(1), 2871(2020)

[112] Xing, S., Wang, X., Guo, E., Kleemann, H., Leo, K.: Organic thin-film red-light photodiodes with tunable spectral response via selective exciton activation. ACS Appl. Mater. Interfaces 12(11), 13061–13067(2020)

[113] Wang, C., Zhang, C., Chen, Q., Chen, L.: Improving the photomultiplication in organic photodetectors with narrowband response by interfacial engineering. Acta Chim. Sin. 79(8), 1030–1036(2021)

[114] Ünlü, M.S., Strite, S.: Resonant cavity enhanced photonic devices. J. Appl. Phys. 78(2), 607–639(1995)

[115] Xiong, J., Wu, S.-T.: Planar liquid crystal polarization optics for augmented reality and virtual reality: From fundamentals to applications. eLight 1(3), 1–20(2021)

[116] Du, Y., Zou, C.L., Zhang, C., Wang, K., Qiao, C., Yao, J., Zhao, Y.S.: Tuneable red, green, and blue single-mode lasing in heterogeneously coupled organic spherical microcavities. Light Sci. Appl. 9(1), 151(2020)

[117] Zang, C., Liu, S., Xu, M., Wang, R., Cao, C., Zhu, Z., Zhang, J., Wang, H., Zhang, L., Xie, W., Lee, C.S.: Top-emitting thermally activated delayed fluorescence organic light-emitting devices with weak light-matter coupling. Light Sci. Appl. 10(1), 116(2021)

[118] Zhao, Z., Xu, C., Ma, Y., Yang, K., Liu, M., Zhu, X., Zhou, Z., Shen, L., Yuan, G., Zhang, F.: Ultraviolet narrowband photomultiplication type organic photodetectors with Fabry–Pérot resonator architecture. Adv. Funct. Mater. 32(29), 2203606(2022)

[119] Wang, J., Ullbrich, S., Hou, J.L., Spoltore, D., Wang, Q., Ma, Z., Tang, Z., Vandewal, K.: Organic cavity photodetectors based on nanometer-thick active layers for tunable monochromatic spectral response. ACS Photon. 6(6), 1393–1399(2019)

[120] Siegmund, B., Mischok, A., Benduhn, J., Zeika, O., Ullbrich, S., Nehm, F., Böhm, M., Spoltore, D., Fröb, H., Körner, C., Leo, K., Vandewal, K.: Organic narrowband near-infrared photodetectors based on intermolecular charge-transfer absorption. Nat. Commun. 8(1), 15421(2017)

[121] Kublitski, J., Fischer, A., Xing, S., Baisinger, L., Bittrich, E., Spoltore, D., Benduhn, J., Vandewal, K., Leo, K.: Enhancing sub-bandgap external quantum efficiency by photomultiplication for narrowband organic near-infrared photodetectors. Nat. Commun. 12(1), 4259(2021)

[122] Wang, Y., Siegmund, B., Tang, Z., Ma, Z., Kublitski, J., Xing, S., Nikolis, V.C., Ullbrich, S., Li, Y., Benduhn, J., Spoltore, D., Vandewal, K., Leo, K.: Stacked dual-wavelength near-infrared organic photodetectors. Adv. Opt. Mater. 9(6), 2001784(2021)

[123] Suganuma, N., Heo, C.J., Minami, D., Yun, S., Park, S., Lim, Y., Fang, F., Choi, B., Park, K.B.: High speed response organic photodetectors with cascade buffer layers. Adv. Electron. Mater. 8(2), 2100539(2022)

[124] Saggar, S., Sanderson, S., Gedefaw, D., Pan, X., Philippa, B., Andersson, M.R., Lo, S.C., Namdas, E.B.: Toward faster organic photodiodes: tuning of blend composition ratio. Adv. Funct. Mater. 31(19), 2010661(2021)

[125] Salamandra, L., La Notte, L., Fazolo, C., Di Natali, M., Penna, S., Mattiello, L., Cinà, L., Del Duca, R., Reale, A.: A comparative study of organic photodetectors based on P3HT and PTB7 polymers for visible light communication. Org. Electron. 81, 105666(2020)

[126] Liu, J., Jiang, J., Wang, S., Li, T., Jing, X., Liu, Y., Wang, Y., Wen, H., Yao, M., Zhan, X., Shen, L.: Fast response organic tandem photodetector for visible and near-infrared digital optical communications. Small 17(43), e2101316(2021)

[127] Shen, L., Fang, Y., Wang, D., Bai, Y., Deng, Y., Wang, M., Lu, Y., Huang, J.: A self-powered, sub-nanosecond-response solution- processed hybrid perovskite photodetector for time-resolved photoluminescence-lifetime detection. Adv. Mater. 28(48), 10794–10800(2016)

[128] Wang, X., Wang, J., Zhao, H., Jin, H., Yu, J.: Detectivity enhancement of double-layer organic photodetectors consisting of solution-processed interconnecting layers. Mater. Lett. 243, 81–83(2019)

[129] Xing, S., Kublitski, J., Hänisch, C., Winkler, L.C., Li, T.Y., Kleemann, H., Benduhn, J., Leo, K.: Photomultiplication-type organic photodetectors for near-infrared sensing with high and bias-independent specific detectivity. Adv. Sci. (Weinh.) 9(7), e2105113(2022)

[130] Shi, L., Liang, Q., Wang, W., Zhang, Y., Li, G., Ji, T., Hao, Y., Cui, Y.: Research progress in organic photomultiplication photodetectors. Nanomaterials (Basel) 8(9), 713(2018)

[131] Yan, Y., Wu, X., Chen, Q., Liu, Y., Chen, H., Guo, T.: High-performance low-voltage flexible photodetector arrays based on all-solid-state organic electrochemical transistors for photosensing and imaging. ACS Appl. Mater. Interfaces 11(22), 20214–20224(2019)

[132] Lv, L., Dang, W., Wu, X., Chen, H., Wang, T., Qin, L., Wei, Z., Zhang, K., Shen, G., Huang, H.: Flexible short-wave infrared image sensors enabled by high-performance polymeric photo-detectors. Macromolecules 53(23), 10636–10643(2020)

[133] Webster, J.G.: Design of pulse oximeters. CRC Press, Boca Raton (1997)

[134] Lochner, C.M., Khan, Y., Pierre, A., Arias, A.C.: All-organic optoelectronic sensor for pulse oximetry. Nat. Commun. 5(1), 5745(2014)

[135] Khan, Y., Han, D., Pierre, A., Ting, J., Wang, X., Lochner, C.M., Bovo, G., Yaacobi-Gross, N., Newsome, C., Wilson, R., Arias, A.C.: A flexible organic reflectance oximeter array. Proc. Natl. Acad. Sci. U.S.A. 115(47), E11015–E11024(2018)

[136] Eun, H.J., Lee, H., Shim, Y., Seo, G.U., Lee, A.Y., Park, J.J., Heo, J., Park, S., Kim, J.H.: Strain-durable dark current in near-infrared organic photodetectors for skin-conformal photoplethysmographic sensors. iScience 25(5), 104194(2022)

[137] Pan, T., Liu, S., Zhang, L., Xie, W., Yu, C.: A flexible, multi-functional, optoelectronic anticounterfeiting device from high-performance organic light-emitting paper. Light Sci. Appl. 11(1), 59(2022)

[138] Yokota, T., Zalar, P., Kaltenbrunner, M., Jinno, H., Matsuhisa, N., Kitanosako, H., Tachibana, Y., Yukita, W., Koizumi, M., Someya, T.: Ultraflexible organic photonic skin. Sci. Adv. 2(4), e1501856(2016)

[139] Khan, Y., Han, D., Ting, J., Ahmed, M., Nagisetty, R., Arias, A.C.: Organic multi-channel optoelectronic sensors for wearable health monitoring. IEEE Access 7, 128114–128124(2019)

[140] Lee, H., Kim, E., Lee, Y., Kim, H., Lee, J., Kim, M., Yoo, H.J., Yoo, S.: Toward all-day wearable health monitoring: an ultralow-power, reflective organic pulse oximetry sensing patch. Sci. Adv. 4(11), eaas9530(2018)

[141] Park, Y., Fuentes-Hernandez, C., Kim, K., Chou, W.F., Larrain, F.A., Graham, S., Pierron, O.N., Kippelen, B.: Skin-like low-noise elastomeric organic photodiodes. Sci. Adv. 7(51), eabj6565(2021)

[142] Pierre, A., Arias, A.C.: Solution-processed image sensors on flexible substrates. Flex. Print. Electron. 1(4), 043001(2016)

[143] Hou, X., Tang, W., Chen, S., Liang, J., Xu, H., Ouyang, B., Li, M., Song, Y., Chen, C.C., Too, P., Wei, X., Jin, L., Qi, G., Guo, X.: Large area and flexible organic active matrix image sensor array fabricated by solution coating processes at low temperature. In: Proceedings of 5th IEEE Electron Devices Technology & Manufacturing Conference (EDTM). IEEE, 1–3(2021).

[144] Wu, Y.L., Fukuda, K., Yokota, T., Someya, T.: A highly responsive organic image sensor based on a two-terminal organic photodetector with photomultiplication. Adv. Mater. 31(43), e1903687(2019)

[145] Tordera, D., van Breemen, A., Kronemeijer, A., van der Steen, J.L., Peeters, B., Shanmugan, S., Akkerman, H., Gelinck, G.: Flexible and large-area imagers using organic photodetectors. In: Organic Flexible Electronics, pp 575–597. Elsevier, Amsterdam (2021).

[146] Yang, W., Qiu, W., Georgitzikis, E., Simoen, E., Serron, J., Lee, J., Lieberman, I., Cheyns, D., Malinowski, P., Genoe, J., Chen, H., Heremans, P.: Mitigating dark current for high-performance near-infrared organic photodiodes via charge blocking and defect passivation. ACS Appl. Mater. Interfaces 13(14), 16766–16774(2021)

[147] Han, M.G., Park, K.B., Bulliard, X., Lee, G.H., Yun, S., Leem, D.S., Heo, C.J., Yagi, T., Sakurai, R., Ro, T., Lim, S.J., Sul, S., Na, K., Ahn, J., Jin, Y.W., Lee, S.: Narrow-band organic photo-diodes for high-resolution imaging. ACS Appl. Mater. Interfaces 8(39), 26143–26151(2016)

[148] Sakai, T., Takagi, T., Imamura, K., Mineo, K., Yakushiji, H., Hashimoto, Y., Aotake, T., Sadamitsu, Y., Sato, H., Aihara, S.: Color-filter-free three-layer-stacked image sensor using blue/green-selective organic photoconductive films with thin-film transistor circuits on CMOS image sensors. ACS Appl. Electron. Mater. 3(7), 3085–3095(2021)

[149] Li, Y., Luo, H., Mao, L., Yu, L., Li, X., Jin, L., Zhang, J.: A solution-processed hole-transporting layer based on p-type CUCRO2 for organic photodetector and image sensor. Adv. Mater. Interfaces 8(20), 2100801(2021)

[150] Baierl, D., Pancheri, L., Schmidt, M., Stoppa, D., Dalla Betta, G.F., Scarpa, G., Lugli, P.: A hybrid CMOS-imager with a solution-processable polymer as photoactive layer. Nat. Commun. 3(1), 1175(2012)

[151] Shekhar, H., Fenigstein, A., Leitner, T., Lavi, B., Veinger, D., Tessler, N.: Hybrid image sensor of small molecule organic photodiode on CMOS-integration and characterization. Sci. Rep. 10(1), 7594(2020)

[152] Wu, P., Ye, L., Tong, L., Wang, P., Wang, Y., Wang, H., Ge, H., Wang, Z., Gu, Y., Zhang, K., Yu, Y., Peng, M., Wang, F., Huang, M., Zhou, P., Hu, W.: Van der Waals two-color infrared photodetector. Light Sci. Appl. 11(1), 6(2022)

[153] Dehzangi, A., Li, J., Razeghi, M.: Band-structure-engineered high-gain LWIR photodetector based on a type-II superlattice. Light Sci. Appl. 10(1), 17(2021)

[154] Feng, Z., Tang, T., Wu, T., Yu, X., Zhang, Y., Wang, M., Zheng, J., Ying, Y., Chen, S., Zhou, J., Fan, X., Zhang, D., Li, S., Zhang, M., Qian, J.: Perfecting and extending the near-infrared imaging window. Light Sci. Appl. 10(1), 197(2021)

[155] Li, C., Wang, H., Wang, F., Li, T., Xu, M., Wang, H., Wang, Z., Zhan, X., Hu, W., Shen, L.: Ultrafast and broadband photodetectors based on a perovskite/organic bulk heterojunction for large-dynamic-range imaging. Light Sci. Appl. 9(1), 31(2020)

[156] Seo, H., Aihara, S., Watabe, T., Ohtake, H., Kubota, M., Egami, N.: Color sensors with three vertically stacked organic photodetectors. Jpn. J. Appl. Phys. 46(49), L1240–L1242(2007)

[157] Lim, S.J., Leem, D.S., Park, K.B., Kim, K.S., Sul, S., Na, K., Lee, G.H., Heo, C.J., Lee, K.H., Bulliard, X., Satoh, R., Yagi, T., Ro, T., Im, D., Jung, J., Lee, M., Lee, T.Y., Han, M.G., Jin, Y.W., Lee, S.: Organic-on-silicon complementary metal-oxide-semiconductor colour image sensors. Sci. Rep. 5(1), 7708(2015)

[158] Sato, S., Yamashita, T., Miyazaki, M.: UHD-2/8K camera recorder using organic cmos image sensor. SMPTE Motion Imaging J. 129(6), 52–60(2020)

[159] Lim, Y., Yun, S., Minami, D., Choi, T., Choi, H., Shin, J., Heo, C.J., Leem, D.S., Yagi, T., Park, K.B., Kim, S.: Green-light-selective organic photodiodes with high detectivity for CMOS color image sensors. ACS Appl. Mater. Interfaces 12(46), 51688–51698(2020)

[160] Banach, M., Markham, S., Agaiby, R., Too, P.: Low leakage organic backplanes for high pixel density optical sensors. SID Symp. Digest Tech. Papers 49(1), 90–91(2018)

[161] Tordera, D., Peeters, B., Akkerman, H.B., Breemen, A.J.J.M., Maas, J., Shanmugam, S., Kronemeijer, A.J., Gelinck, G.H.: A high-resolution thin-film fingerprint sensor using a printed organic photodetector. Adv. Mater. Technol. 4(11), 1900651(2019)

[162] Kamada, T., Hatsumi, R., Watanabe, K., Kawashima, S., Katayama, M., Adachi, H., Ishitani, T., Kusunoki, K., Kubota, D., Yamazaki, S.: OLED display incorporating organic photodiodes for fingerprint imaging. J. Soc. Inf. Disp. 27(6), 361–371(2019)

[163] Xu, Y., Ruan, C., Zhou, L., Zou, J., Xu, M., Wu, W., Wang, L., Peng, J.A.: 256 × 256 50-µm pixel pitch OPD image sensor based on an IZO TFT backplane. IEEE Sens. J. 21(18), 20824–20832(2021)

[164] Eckstein, R., Strobel, N., Rödlmeier, T., Glaser, K., Lemmer, U., Hernandez-Sosa, G.: Fully digitally printed image sensor based on organic photodiodes. Adv. Opt. Mater. 6(5), 1701108(2018)

[165] Posar, J.A., Davis, J., Alnaghy, S., Wilkinson, D., Cottam, S., Lee, D.M., Thompson, K.L., Holmes, N.P., Barr, M., Fahy, A., Nicolaidis, N.C., Louie, F., Fraboni, B., Sellin, P.J., Lerch, M.L.F., Rosenfeld, A.B., Petasecca, M., Griffith, M.J.: Polymer photodetectors for printable, flexible, and fully tissue equivalent X-ray detection with zero-bias operation and ultrafast temporal responses. Adv. Mater. Technol. 6(9), 2001298(2021)

[166] van Breemen, A.J.J.M., Simon, M., Tousignant, O., Shanmugam, S., van der Steen, J.-L., Akkerman, H.B., Kronemeijer, A., Ruetten, W., Raaijmakers, R., Alving, L., Jacobs, J., Malinowski, P.E., De Roose, F., Gelinck, G.H.: Curved digital X-ray detectors. NPJ Flex. Electron. 4(1), 1–8(2020)

[167] Li, A., Yao, C., Xia, J., Wang, H., Cheng, Q., Penty, R., Fainman, Y., Pan, S.: Advances in cost-effective integrated spectrometers. Light Sci. Appl. 11(1), 174(2022)

[168] Yang, Z., Albrow-Owen, T., Cai, W., Hasan, T.: Miniaturization of optical spectrometers. Science 371(6528), eabe0722(2021)

[169] Vega-Colado, C., Arredondo, B., Torres, J.C., López-Fraguas, E., Vergaz, R., Martín-Martín, D., Del Pozo, G., Romero, B., Apilo, P., Quintana, X., Geday, M.A., De Dios, C., Sánchez-Pena, J.M.: An all-organic flexible visible light communication system. Sensors (Basel) 18(9), 3045(2018)

[170] Haigh, P.A., Ghassemlooy, Z., Le Minh, H., Rajbhandari, S., Arca, F., Tedde, S.F., Hayden, O., Papakonstantinou, I.: Exploiting equalization techniques for improving data rates in organic optoelectronic devices for visible light communications. J. Lightwave Technol. 30(19), 3081–3088(2012)

[171] Dong, Y., Shi, M., Yang, X., Zeng, P., Gong, J., Zheng, S., Zhang, M., Liang, R., Ou, Q., Chi, N., Zhang, S.: Nanopatterned luminescent concentrators for visible light communications. Opt. Express 25(18), 21926–21934(2017)

[172] Cao, J., Shan, T., Wang, J.K., Xu, Y.X., Ren, X., Zhong, H.: Stereoisomerism of ladder-type acceptor molecules and its effect on photovoltaic properties. Dyes Pigments 165, 354–360(2019)

[173] Chi, N., Hu, F., Zhou, Y.: The challenges and prospects of high-speed visible light communication technology. ZTE Technol. J. 25(5), 56–61(2019)

[174] Li, L., Zhao, H., Liu, C., Li, L., Cui, T.J.: Intelligent metasurfaces: control, communication and computing. eLight 2(7), 1–24(2022)

[175] Tavakkolnia, I., Jagadamma, L.K., Bian, R., Manousiadis, P.P., Videv, S., Turnbull, G.A., Samuel, I.D.W., Haas, H.: Organic photovoltaics for simultaneous energy harvesting and high-speed MIMO optical wireless communications. Light Sci. Appl. 10(1), 41(2021)

[176] Ghassemlooy, Z., Haigh, P.A., Arca, F., Tedde, S.F., Hayden, O., Papakonstantinou, I., Rajbhandari, S.: Visible light communications: 375 Mbits/s data rate with a 160 kHz bandwidth organic photodetector and artificial neural network equalization. Photon. Res. 1(2), 65(2013)

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