Regulating the crystal orientation of vapor-transport-deposited GeSe thin films by a post-annealing treatment

Recently, GeSe has emerged as a highly promising photovoltaic absorber material due to its excellent optoelectronic properties, nontoxicity, and high stability. Although many advantages make GeSe well suited for thin-film solar cells, the power conversion efficiency of the GeSe thin-film solar cell is still much below the theoretical maximum efficiency. One of the challenges lies in controlling the crystal orientation of GeSe to enhance solar cell performance. The two-step preparation of GeSe thin films has not yet been reported to grow along the [111] orientation. In this work, we study the effect of a post-annealing treatment on the GeSe thin films and the performance of the solar cells. It was found that amorphous GeSe films can be converted into polycrystalline films with different orientations by changing the post-annealing temperature. [111]-oriented and [100]-oriented GeSe thin films were successfully prepared on the same substrate by optimizing the annealing conditions. With the structure of Au/GeSe/CdS/ITO cell devices, PCEs of 0.14% and 0.16% were ultimately achieved.