Solvent engineering for high-performance silver sulfide thin film solar cells

Silver sulfide (Ag₂S) is one of the best photovoltaic materials in terms of elemental composition and both chemical stability and device stability. However, the lack of suitable film processing methods severely limits the power conversion efficiency (PCE) improvement of Ag₂S-based devices. Here, we propose a specific solvent engineering train for high-quality Ag₂S absorber films by precisely tuning the dimethyl sulfoxide (DMSO)/N,N-dimethylformamide (DMF) constituent and post-deposition annealing temperature. A preferential transition in crystal orientation from (012) to ( $\overline{1}03$) crystal planes is found to play a key role in photo-induced carrier behavior. The film surface morphology and grain size are fine-tuned, while the bulk defect concentration and mitigated interface carrier recombination are well suppressed. The optimized simple indium tin oxide (ITO)/Ag₂S/2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (Spiro-OMeTAD)/Au device exhibits a significant increase in PCE from 0.77% to 2.57%, which is currently the highest value among the reported literatures of Ag₂S solar cells without an electron transport layer.