Hybrid organic–inorganic perovskite solar cells (PSCs) present a leading thin-film photovoltaic technology with superior solar-to-electric power conversion efficiencies. The most effective compositions, however, contain lead cations, which are toxic and pose environmental hazards. One of the alternatives to lead-based perovskite materials is silver bismuth halide analogues. Here, we present a comprehensive investigation of different silver bismuth iodide compositions by means of density functional theory calculations (DFT) as well as X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy measurements. Through our combined experimental and theoretical study, we have discovered that silver bismuth iodides possess several intrinsic limitations, such as limited charge transport and localized electronic states, owing to the presence of vacant sites. Such limitations result in moderate solar cell efficiencies, significantly lower than those of lead halide perovskites. However, we suggest the possibility of increasing efficiencies by adding BiCl₃ to the precursor solution, yielding one of the highest efficiencies reported for this class of compounds to date. This highlights the potential of compositional engineering for these lead-free solar cell materials.