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Frontiers of Optoelectronics

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, Volume 11 Issue 4 Previous Issue   
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EDITORIAL
REVIEW ARTICLE
Progress on photochromic diarylethenes with aggregation induced emission
Nuo-Hua XIE, Ying CHEN, Huan YE, Chong LI, Ming-Qiang ZHU
Front. Optoelectron.. 2018, 11 (4): 317-332.  https://doi.org/10.1007/s12200-018-0839-4
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Among various photochromic compounds, diarylethenes (DAEs) have been widely studied and applied due to their excellent thermal bistability and fatigue resistance. Most researches are focused on the properties and applications of DAEs in solution. However, they meet the problem of fluorescence quenching at high concentration or at solid state which limits their performance in the practical applications. Fortunately, the DAE based photochromic aggregation-induced emission (AIE) materials do well in addressing this problem. This work here reviews the current research progress on the structures, properties and applications of the DAE based photochromic AIE materials and points out some existing problems so as to promote subsequent development of this field in the future.

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Recent advances in solar cells and photo-electrochemical water splitting by scanning electrochemical microscopy
Xiaofan ZHANG, Man LIU, Weiqian KONG, Hongbo FAN
Front. Optoelectron.. 2018, 11 (4): 333-347.  https://doi.org/10.1007/s12200-018-0852-7
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Investigation on the mechanism and kinetics of charge transfer at semiconductor/electrolyte interface is significant for improving the photoelectric conversion efficiency and developing novel and high-efficiency photovoltaic devices. Scanning electrochemical microscopy (SECM), as a powerful analytical technique, has a potential advantage of high spatial and temporal resolution. It has been expanded into a broad range of research fields since the first inception of SECM in 1989 by Bard groups, which includes biological, enzymes, corrosion, energy conversion and storage (such as solar cells, hydrogen and battery). Herein, we review the basic principles and the development of SECM, and chiefly introduce the recent advances of SECM investigation in photoelectrochemical (PEC) cells including solar cells and PEC water splitting. These advances include rapid screening of photocatalysts/photoelectrodes, interfacial reaction kinetics and quantitation of reaction intermediates, which is significant for evaluating the performance, choosing catalysts and developing novel composite photoanodes and high efficiency devices. Finally, we briefly describe the development trends of SECM in energy research.

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RESEARCH ARTICLE
Ether chain functionalized fullerene derivatives as cathode interface materials for efficient organic solar cells
Jikang LIU, Junli LI, Guoli TU
Front. Optoelectron.. 2018, 11 (4): 348-359.  https://doi.org/10.1007/s12200-018-0842-9
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The electron transport layer (ETL) plays a crucial role on the electron injection and extraction, resulting in balanced charge transporting and reducing the interfacial energy barrier. The interface compatibility and electrical contact via employing appropriate buffer layer at the surface of hydrophobic organic active layer and hydrophilic inorganic electrode are also essential for charge collections. Herein, an ether chain functionalized fullerene derivatives [6,6]-phenyl-C61-butyricacid-(3,5-bis(2-(2-ethoxyethoxy)-ethoxy)-phenyl)-methyl ester (C60-2EPM) was developed to modify zinc oxide (ZnO) in inverted structure organic solar cells (OSCs). The composited ZnO/C60-2EPM interface layer can help to overcome the low interface compatibility between ZnO and organic active layer. By introducing the C60-2EPM layer, the composited fullerene derivatives tune energy alignment and accelerated the electronic transfer, leading to increased photocurrent and power conversion efficiency (PCE) in the inverted OSCs. The PCE based on PTB7-Th:PC71BM was enhance from 8.11% on bare ZnO to 8.38% and 8.65% with increasing concentrations of 2.0 and 4.0 mg/mL, respectively. The fullerene derivatives C60-2EPM was also used as a third compound in P3HT:PC61BM blend to form ternary system, the devices with addition of C60-2EPM exhibited better values than the control device.

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High fill factor over 82% enabled by a biguanide doping electron transporting layer in planar perovskite solar cells
Ru GE, Fei QIN, Lin HU, Sixing XIONG, Yinhua ZHOU
Front. Optoelectron.. 2018, 11 (4): 360-366.  https://doi.org/10.1007/s12200-018-0847-4
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N-type doping in electron transport materials is an effective way to improve the electron collection and enhance the performance of the perovskite solar cells (PSCs). Here, for the first time, an antibiotic and antimicrobial compound of 1-(o-Tolyl) biguanide (oTb) is used to dope the electron transport material of phenyl-C61-butyric acid methyl ester (PCBM). The oTb doping into the PCBM can increase the conductivity and reduce the work function of the PCBM. The oTb doping can significantly enhance the fill factor (FF) of the perovskite solar cells with the structure of glass/ITO/NiOx/MAPbI3/(oTb)PCBM/(PEIE)/Ag. For the cells without PEIE (polyethylenimine ethoxylated) coating, the oTb doping increases the FF from 0.57 to 0.73. S-shaped of the current density-voltage (J-V) characteristic under illumination is removed after the oTb doping. For the cells with PEIE coating between the (oTb)PCBM and Ag, the oTb doping increases the FF from 0.70 to 0.82. These results show the potential of the oTb as an n-dopant in the applications of perovskite solar cells.

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BiOI/WO3 photoanode with enhanced photoelectrochemical water splitting activity
Weina SHI, Xiaowei LV, Yan SHEN
Front. Optoelectron.. 2018, 11 (4): 367-374.  https://doi.org/10.1007/s12200-018-0835-8
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This work reports on a novel BiOI/WO3 composite photoanode, which was fabricated by depositing BiOI onto a WO3 nanoflake electrode through a electrodeposition method. The photoelectrochemical (PEC) activity of the BiOI/WO3 electrode for water splitting under visible-light irradiation was evaluated. The results show that the BiOI/WO3 photoanode achieved a photocurrent density of 1.21 mA·cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE), which was higher than that of the bare WO3 nanoflake electrode (0.67 mA·cm−2). The enhanced PEC acticity of BiOI/WO3 for water splitting can be attributed to the expansion of light absorption range as well as the facilitated separation of photo-generated carriers.

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Efficient deep red phosphorescent OLEDs using 1,2,4-thiadiazole core-based novel bipolar host with low efficiency roll-off
Runda GUO, Wenzhi ZHANG, Qing ZHANG, Xialei LV, Lei WANG
Front. Optoelectron.. 2018, 11 (4): 375-384.  https://doi.org/10.1007/s12200-018-0855-4
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A series of 1,2,4-thiadiazole core-based bipolar materials, 2,2'-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (o-TPATHZ), 3,3′-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (m-TPATHZ) and 4,4'-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (p-TPATHZ) were developed as the host matrixes for the deep red phosphorescent emitters tris(1-phenylisoqiunoline)iridium (Ir(piq)3) and [bis(2-methyldibenzo-[f,h]-quinoxaline)Ir(III)(acetylacetonate)] (Ir(MDQ)2(acac)). By systematic studying, we demonstrated that there are two types of charge-trapping effect within the emissive layers through adjusting the host-guest compatibility. And, it is revealed that a symmetric charge-trapping effect can contribute to realizing a stable charge-balance, which led to a mitigating efficiency roll-off at high current density. Consequently, a maximum external quantum efficiency (EQE) of 16.2% was achieved by an optimized device with p-TPATHZ-Ir(piq)3 emissive layer. Remarkably, the EQE still remained as high as 15.7% at the high luminance of 1000 cd/m2.

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Luminescent disordered nanostructures: synthesis and characterization of CdSe nano-agglomerates
Ruiqing HU, Yifeng SHI, Haifeng BAO
Front. Optoelectron.. 2018, 11 (4): 385-393.  https://doi.org/10.1007/s12200-018-0822-0
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A disorderly nanostructured CdSe nano-agglomerates (NAs) with tunable emission are synthesized in aqueous solution. Although the CdSe NAs have diameters of about 20 nm that are larger than the Bohr radius of the crystal bulk, they show size-dependent emission similar to the CdSe nanocrystals. The CdSe NAs represent a collective energy state based on Anderson localization.

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Influence of cerium ions on thermal bleaching of photo-darkened ytterbium-doped fibers
Xiaoxia LIU, Chaoping LIU, Gui CHEN, Haiqing LI
Front. Optoelectron.. 2018, 11 (4): 394-399.  https://doi.org/10.1007/s12200-018-0832-y
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We studied the influence of cerium (Ce) ions on photo-darkening (PD) behavior in ytterbium/aluminum (Yb/Al) co-doped silica fibers at room and elevated temperatures. Low levels of PD was observed for Ce co-doped Yb/Al fiber. And the Yb/Al co-doped fiber was completely bleached at ~600°C. The addition of Ce ions as co-dopant can significantly lower the initial recovery and complete bleaching temperatures. The complete recovery temperature is ~ 450°C and ~400°C for Yb/Al/Ce low fiber and Yb/Al/Ce high fiber respectively. More importantly, Ce co-doping in Yb/Al fiber also decreases the heat-induced loss.

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Temperature dependence simulation and characterization for InP/InGaAs avalanche photodiodes
Yanli ZHAO, Junjie TU, Jingjing XIANG, Ke WEN, Jing XU, Yang TIAN, Qiang LI, Yuchong TIAN, Runqi WANG, Wenyang LI, Mingwei GUO, Zhifeng LIU, Qi TANG
Front. Optoelectron.. 2018, 11 (4): 400-406.  https://doi.org/10.1007/s12200-018-0851-8
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Based on the newly proposed temperature dependent dead space model, the breakdown voltage and bandwidth of InP/InGaAs avalanche photodiode (APD) have been investigated in the temperature range from -50°C to 100°C. It was demonstrated that our proposed model is consistent with the experimental results. Our work may provide a guidance to the design of APDs with controllably low temperature coefficient.

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Proposal for CEP measurement based on terahertz air photonics
Kejia WANG, Xinyang GU, Jinsong LIU, Zhengang YANG, Shenglie WANG
Front. Optoelectron.. 2018, 11 (4): 407-412.  https://doi.org/10.1007/s12200-018-0845-6
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Single-shot carrier envelope phase (CEP) measurement is a challenge in the research field of ultrafast optics. We theoretically investigate how an intense terahertz pulse modulates second harmonic emission (SH) from a gas plasma induced by a few-cycle laser pulse (FCL). Results show that the modulation quantity of SH intensity has a cosinoidal dependence on the CEP of FCL pulses, based on which we propose a low energy, all-optical method for single-shot CEP measurements via using a known intense terahertz pulse. Moreover, we propose an experimental realization.

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A direct method to calculate second-order two-dimensional terahertz spectroscopy in frequency-domain based on classical theory
Feidi XIANG, Kejia WANG, Zhengang YANG, Jinsong LIU, Shenglie WANG
Front. Optoelectron.. 2018, 11 (4): 413-418.  https://doi.org/10.1007/s12200-018-0863-4
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Previous theoretical researches on the two-dimensional terahertz spectroscopy (2DTS), which are conducted via inefficiently time-consuming numerical simulation, deal with only single-mode system. To overcome the limitations, we derive a classical-theory-based analytical solution which is applicable to multi-modes system. Three typical weak sources of nonlinearities are introduced. The findings suggest that the analytical results correspond well with those obtained by the traditional numerical simulation. Thus the study provides a more efficient and practical method to directly calculate 2DTS, and, in a broader sense, sheds new light on the theory of 2DTS.

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