Coexistence of Photoelectric Conversion and Storage in van der Waals Heterojunctions
Yucheng Jiang, Anpeng He, Run Zhao, Yu Chen, Guozhen Liu, Hao Lu, Jinlei Zhang, Qing Zhang, Zhuo Wang, Chen Zhao, Mingshen Long, Weida Hu, Lin Wang, Yaping Qi, Ju Gao, Quanying Wu, Xiaotian Ge, Jiqiang Ning, Andrew T. S. Wee, Cheng-Wei Qiu
Abstract
Van der Waals (vdW) heterojunctions, based on two-dimensional (2D) materials, have great potential for the development of ecofriendly and high-efficiency nanodevices, which shows valuable applications as photovoltaic cells, photodetectors, etc. However, the coexistence of photoelectric conversion and storage in a single device has not been achieved until now. Here, we demonstrate a simple strategy to construct a vdW p-n junction between a WSe_{2} layer and quasi-2D electron gas. After an optical illumination, the device stores the light-generated carriers for up to seven days, and then releases a very large photocurrent of 2.9 mA with bias voltage applied in darkness; this is referred to as chargeable photoconductivity (CPC), which completely differs from any previously observed photoelectric phenomenon. In normal photoconductivity, the recombination of electron-hole pairs occurs at the end of their lifetime; in contrast, infinite-lifetime photocarriers can be generated and stored in CPC devices without recombination. The photoelectric conversion and storage are completely self-excited during the charging process. The ratio between currents in full- and empty-photocarrier states below the critical temperature reaches as high as 10^{9}, with an external quantum efficiency of 93.8% during optical charging. A theoretical model developed to explain the mechanism of this effect is in good agreement with the experimental data. This work paves a path toward the high-efficiency devices for photoelectric conversion and storage.