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(a)Ag(m1)Bi(m2)I(n)/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(a)Ag(m1)Bi(m2)I(n) could be reduced from 2.06 to 1.78 eV. Solar cells with the structure of FTO/TiO(2)/Cu(a)Ag(m1)Bi(m2)I(n)/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. [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40820-023-01033-5.