Ag-(Bi, Sb, In, Ga)-I Solar Cells: Impacts of Elemental Composition and Additives on the Charge Carrier Dynamics and Crystal Structures

Silver-bismuth-iodide (Ag-Bi-I) semiconductors have increasingly gathered much attention as an alternative to lead halide perovskites. However, Ag-Bi-I has not been thoroughly investigated owing to the complexity in its composition and solution process, and the power conversion efficiency (PCE) of its solar cell devices has still stayed at a low level. Here, we report a rigorous exploration of the Ag-M-I composition and III–V elements (M = bismuth, antimony, indium, and gallium) via effective guidance of time-resolved microwave conductivity (TRMC) measurements. The screening of the Ag:Bi precursor ratio reveals the superior TRMC transients at the low Bi content to those at the high Bi content, which relates to the predominant Ag2BiI5 and AgBi2I7 phases, respectively, and leads to the higher PCE in the former. The addition of hydroiodic acid (HI) and the mixing of the III–V elements show dramatic effects on the charge carrier dynamics. We obtain an improved PCE of 1.82% in the Ag-(Bi/Sb)-I composite compared to the initial 0.78% of Ag-Bi-I without additive, which broadens the library of Ag-M-I semiconductors for further evolution of lead-free solar cells.