Boosting the efficiency of GeSe solar cells by low-temperature treatment of p-n junction

Germanium monoselenide (GeSe) is an emerging promising photovoltaic absorber material due to its attractive optoelectronic properties as well as non-toxic and earth-abundant constitutes. However, all previously reported GeSe solar cells rely on a superstrate configuration coupled with a CdS buffer layer, and suffer from unsatisfactory performance. Here we demonstrate that this low efficiency arises from the inevitable high-temperature treatment of p-n junction in superstrate configuration. This results in the diffusion of Cd atoms from CdS layer into GeSe film that introduces detrimental deep trap states inside the bandgap of GeSe (similar to 0.34 eV below conduction band minimum). We adopt therefore a substrate configuration that enables the deposition of CdS atop pre-deposited polycrystalline GeSe film at room temperature, avoiding the Cd diffusion. By optimizing the annealing temperature of complete devices via a highthroughput screening method, the resulting substrate solar cells annealed at 150 degrees C achieve an efficiency of 3.1%, two times that of the best previously reported superstrate GeSe results.

Automated summary

Germanium monoselenide (GeSe) is a promising photovoltaic absorber material, but traditional solar cells based on this material have low efficiency. By using a substrate configuration and optimizing the annealing temperature, the efficiency of GeSe solar cells has been significantly improved.