Ultra-thin (also known as ultra-flexible) organic photovoltaics (OPVs) represent a strong contender among emerging photovoltaic technologies. However, due to the imbalance between the optical and electrical properties of indium tin oxide (ITO)-free transparent electrodes, the ultra-thin OPVs often exhibit lower efficiency compared to the brittle yet more balanced rigid ITO counterparts. Here, we design and fabricate an advanced ultra-thin OPV, which involves a thoroughly optimized silver nanowires (AgNWs) transparent electrode (named AZAT) with excellent optical, electrical and mechanical properties. Specifically, the high-kinetic energy spray-coating method successfully yields a curve-shaped, tightly connected and uniformly distributed AgNWs film, complemented by a capping layer of zinc oxide:aluminum-doped zinc oxide (ZnO:AZO) to improve charge collection capability. Simultaneously, the transparency of the electrode is enhanced through precise optical optimization. Thus, we implant the AZAT-based devices on 1.3 μm polyimide substrates and demonstrate ultra-thin OPVs with a record efficiency of 18.46% and a power density of 40.31 W g-1, which is the highest value for PV technologies. Encouragingly, the AZAT electrode also enables the 10.0 cm2 device to exhibit a high efficiency of 15.67%. These results provide valuable insights for the development of ultra-thin OPVs with high efficiency, low cost, superior flexibility, and up-scaling capacity.
Traditionally, squaraine dyes have been studied and employed in biomedical research due to their excellent optical properties, and the molecules are being adopted in different research fields such as organic solar cells. In this study, we investigate correlations between solar cell performance and processing parameters of all-small-molecule bulk heterojunction solar cells comprising squaraine (SQ) as electron donor (D) and non-fullerene small molecules (e.g., ITIC) as electron acceptor (A) with the help of machine learning (ML) and design of experiment (DoE) methods. Among the five predictive ML models tested with the selected parameters, the eXtreme gradient boosting model shows the satisfactory results with quite high coefficient of determination of 0.999 and 0.997 in training and testing sets, respectively. By measuring the contribution of each input variable to solar cell efficiency, four process parameters, that is, the total concentration, the ratio of D/A, the rotational speed of spin coating, and the annealing temperature, are found to be the key features strongly correlated to solar cell efficiency. From contour plots in DoE, the highest solar cell efficiency of approximately 5% can be predicted under the conditions of 15 mg mL-1 in solution concentration, a 1:2 mix ratio of D and A, rotational speeds ranging from 800 to 900 rpm, and annealing temperatures within 100–110°C. Using the suggested parameter conditions, we fabricated solar cells, achieving a quite high efficiency of approximately 4%. Besides the global optimization conditions, we also employ the solvent vapor annealing combination to the thermal annealing to facilitate further mobilization of molecules and more optimized microstructure of bulk heterojunction films, resulting in a further enhancement in solar cell efficiency of more than 20%.
Flexible thermoelectric generators (FTEGs) represent an excellent solution for energizing wearable electronics, capitalizing on their ability to transform body heat into electrical energy. Nevertheless, their use in the wearable industry is limited by the insufficient thermoelectric (TE) efficiency of materials and the minimal temperature variation among the devices. In this study, we have developed a Lego-like reconfigurable FTEG by combining flexible TE chips, rheological liquid-metal electrical wiring, and a stretchable substrate in a mechanical plug-in configuration. The flexible TE chips are constructed from n-type all-inorganic MXene/Bi2Te3 composite films, which have their TE properties further enhanced through heat treatment. A demonstration of the FTEG illustrates its capability to convert heat into vertical temperature difference (ΔT), leading to a substantial ΔT at the cold end in contact with the environment, resulting in a power output of 7.1 µW with a ΔT of 45 K from only 5 TE chips. The reconfigurable FTEG presents significant potential for wearable devices to harness low-grade heat.
Pixelated color convertor plays an immensely important role in nextgeneration display technologies. However, the inherent randomness of light propagation within the convertor presents a formidable challenge to reconcile the huge contradiction between excitation and outcoupling. Here, we demonstrate a bioinspired photonic waveguide pixelated color convertor (BPW-PCC) to realize directional excitation and outcoupling, which is inspired by an insect visual system. The lens array of BPW-PCC enables a focusing photonic waveguide that guides the excitation light and converges it on colloidal quantum dots; the directional channel provides a splitting photonic waveguide to enhance the outcoupling of photoluminescence light. Consequently, the excitation and outcoupling efficiency can be simultaneously improved at this judiciously designed pixelated color convertor with a thickness of 50 µm. By this strategy, ultrathin BPW-PCCs with 4.4-fold enhanced photoluminescence intensity have been demonstrated in micro-light-emitting diode devices and achieved a record-high luminous efficacy of 1600 lm W-1 mm-1, opening a new avenue for efficient miniaturized displays.
Electroconductive hydrogels (ECHs) have been extensively explored as promising flexible materials for bioelectronics because of their tunable conductivity and tissue-like biological and mechanical properties. ECHs can interact intimately with biosystems, transmit physiological signals, and are expected to revolutionize the convergence between organisms and electronics. However, there are still some challenges in utilizing ECHs as flexible materials for bioelectronics, such as mismatched stretchability with tissues, a lack of environmental adaptability, susceptibility to mechanical damage, inferior interface compatibility, and vulnerability to bacterial contamination. This review categorizes these challenges encountered in the bioelectronic applications of ECHs and elaborates on the strategies and theories for improving their performance. Furthermore, we present an overview of the recent advancements in ECHs for bioelectronic applications, specifically focusing on their contributions to healthcare monitoring, treatment of diseases, and human–machine interfaces. The scope of future research on ECHs in bioelectronics is also proposed. Overall, this review offers a comprehensive exposition of difficult issues and potential opportunities for ECHs in bioelectronics, offering valuable insights for the design and fabrication of ECH-based bioelectronic devices.
Thin films with two-dimensional (2D) nanostructures possess good environmental stability, thinner thickness and large surface area, which are widely used as a promising modified electrode material in the field of energy storage, supercapacitors, electrochemical sensors and biosensors. Herein, unique bimetallic ions modified polypyrrole/graphene oxide (PPy/GO) nanosheets, including Co2+-Zr4+/(2-MeIm)x@PPy/GO and Co2+-Run+/(2-MeIm)x@PPy/GO (n = 0, 4), are prepared by using 2-methylimidazolium (2-MeIm) as the linkers between PPy/GO and metal ions. The obtained electrodes constructed by Co2+-Run+/(2-MeIm)x@PPy/GO (n = 0, 4) and Co2+-Zr4+/(2-MeIm)x@PPy/GO exhibit improved capacitor electrochemical properties due to the reversible redox reaction, the large specific surface area and the high theoretical specific capacitance value of the metal ions compared to the unmodified PPy/GO. Especially, the specific capacitance value of Co2+-Run+/(2-MeIm)x@PPy/GO (n = 0, 4) electrode reaches 321.78 F g-1 at a current density of 1 A g-1 and the capacitance retention rate is achieved to 100% in the long cycle charge/discharge test after 10 000 cycles (10 A g-1). It will provide a practical experience for the design and preparation of supercapacitors based on bimetallic ions modified PPy/GO.