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