Cuprous oxide (Cu2O) is a nontoxic and earth‐abundant semiconductor material, which is a promising candidate for low‐cost photovoltaic applications. Although Cu2O‐based solar cells have been studied for a few decades, they still suffer from disappointing photovoltaic performance due to its high trap‐state density and inferior carrier collection efficiency. Herein, a facile solution method is demonstrated to synthesize high‐quality Cu2O films with low defects as hole transport layers (HTLs) and the Cu2O/Si heterojunction solar cells are fabricated. Moreover, a variety of interfacial engineering and light management strategies are adopted to push the efficiency limit of Cu2O/Si solar cells, including a Ag transparent conductive layer, HNO3 passivation, Mg electrode back contact, and MoOx antireflection layer, which enable the boosting of carrier separation and reduce the loss of incident solar light, yielding a record high power conversion efficiency of 9.54%. This work may pave the way for economical and environment‐friendly use of Cu2O/Si heterojunction solar cells in daily life.

Cuprite, nominally cuprous oxide (Cu2O) but more correctly Cu2–x O, is widely used in optoelectronic applications because of its natural p-type, nontoxicity, and abundant availability. However, the photoresponsivity of Cu2O/Si photodetectors (PDs) has been limited by the lack of high-quality Cu2–x O films. Herein, we report a facile room-temperature solution method to prepare high-quality Cu2–x O films with controllable x value which were used as hole selective transport layers in crystalline n-type silicon-based heterojunction PDs. The detection performance of Cu2–x O/Si PDs exhibits a remarkable improvement via reducing the x value, resulting in the optimized PDs with high responsivity of 417 mA W–1 and fast response speed of 1.3 μs. Furthermore, the performance of the heterojunction PDs can be further improved by designing the pyramidal silicon structure, with enhanced responsivity of 600 mA W–1 and response speed of 600 ns. The superior photodetecting performance of Cu2–x O/n-Si heterojunctions is attributed to (i) the matched energy level band alignment, (ii) the low trap states in high-quality Cu2O thin films, and (iii) the excellent light trapping. We expect that the low-cost, highly efficient solution process would be of great convenience for large-scale fabrication of the Cu2–x O thin films and broaden the applications of Cu2–x O-based optoelectronic devices.

Photodetectors (PDs) as image sensors have been widely used in imaging system due to their outstanding photosensitivity. The improvement of imaging quality (signal-to-noise ratio (SNR)) can be realized by reducing the dark current of PDs. Conventionally, interfacial engineering can effectively suppress the dark current of PDs. Nevertheless, these techniques are hard to be applied in practical imaging systems owing to their complicated process. In this work, we proposed a facile method to reduce the dark current of Cu2O/Au Schottky PDs, and further demonstrated its application in high SNR imaging system. By applying a small external bias of −120 μV, the dark current of PDs decreases from 27 nA to 0.6 nA, with 4023% improvements of ON/OFF ratio. Additonaly, a model based on free carriers generated by rich trap-state and thermal excitation under asymmetric internal electric field was proposed to understand this phenomenon. Finally, a high-resolution image with high SNR (48 dB) was acquired, which is close to that of commercial Si-CDD and CMOS. Our results provide a convenient way to reduce the dark current and improve the image quality, also suggest Cu2O is potentially an attractive candidate to be applied in optical imaging applications.