Hydrazine-free precursor for solution-processed all-inorganic Se and Se1−xTex photovoltaics

Abstract

Selenium (Se) has reemerged as a promising absorber material for indoor and tandem photovoltaics (PVs), and its alloys with Te (Se_1−xTe_x) offer a widely tunable bandgap. Solution processing of this materials system offers a route to low-cost fabrication. However, solution processing of Se has, thus far, only used hydrazine, which is an extremely hazardous solvent. In this work, we prepare and isolate propylammonium poly-Se and poly-Se–Te precursors from a safer thiol-amine solvent system. We formulate molecular inks by dissolving the precursor in dimethylformamide (DMF) with a monoethanolamine (EA) additive and process high-quality Se and Se_1−xTe_x films with bandgaps ranging from 1.20 eV to 1.86 eV. We fabricate PVs from these films using TiO₂ and MoO₃ charge transport layers (CTLs) to achieve power conversion efficiencies as high as 2.73% for Se and 2.33% for Se_0.7Te_0.3 under solar simulation. Se devices show excellent stability with no degradation after 1 month in air, enabled by the excellent stability of Se and the use of inorganic CTLs. This work represents an important step towards low-cost solution-phase processing of Se and Se_1−xTe_x alloys for PVs and photodetectors with low toxicity and high bandgap tunability.