One-Step Gas-Solid-Phase Diffusion-Induced Elemental Reaction for Bandgap-Tunable Cu a Ag m1 Bi m2 I n /CuI Thin Film Solar Cells

Lead-free inorganic copper-silver-bismuth-halide materials have attracted more and more attention due to their environmental friendliness, high element abundance, and low cost. Here, we developed a strategy of one-step gas-solid-phase diffusion-induced reaction to fabricate a series of bandgap-tunable Cu Ag Bi I /CuI bilayer films due to the atomic diffusion effect for the first time. By designing and regulating the sputtered Cu/Ag/Bi metal film thickness, the bandgap of Cu Ag Bi I could be reduced from 2.06 to 1.78 eV. Solar cells with the structure of FTO/TiO /Cu Ag Bi I /CuI/carbon were constructed, yielding a champion power conversion efficiency of 2.76%, which is the highest reported for this class of materials owing to the bandgap reduction and the peculiar bilayer structure. The current work provides a practical path for developing the next generation of efficient, stable, and environmentally friendly photovoltaic materials.