GeSe Thin-Film Solar Cells Fabricated by Self-Regulated Rapid Thermal Sublimation

GeSe has recently emerged as a promising photovoltaic absorber material due to its attractive optical and electrical properties as well as earth-abundant and low-toxic constituent elements. However, no photovoltaic device has been reported based on this material so far, which could be attributed to the inevitable coexistence of phase impurities Ge and GeSe₂, leading to detrimental recombination-center defects and seriously degrading the device performance. Here we overcome this issue by introducing a simple and fast (4.8 μm min^-1) rapid thermal sublimation (RTS) process designed according to the sublimation feature of the layered structured GeSe. This new method offers a compelling combination of assisting raw material purification to suppress deleterious phase impurities and preventing the formation of detrimental point defects through congruent sublimation of GeSe, thus providing an in situ self-regulated process to fabricate high quality polycrystalline GeSe films. Solar cells fabricated following this process show a power conversion efficiency of 1.48% with good stability. This preliminary efficiency and high stability, combined with the self-regulated RTS process (also extended to the fabrication of other binary IV-VI chalcogenide films, i.e., GeS), demonstrates the great potential of GeSe for thin-film photovoltaic applications.