Highlights: The CuaAgm1Bim2In/CuI bilayer films are prepared simultaneously in situ by a one-step low-temperature gas-solid phase diffusion induced elemental reaction without spin coating.A new type of CuaAgm1Bim2In photovoltaic material was originally designed to reduce the bandgap of this class of materials from 2.06 to 1.78 eV by breaking the restriction of double perovskite structure with a ratio of Ag:Bi = 1:1.The power conversion efficiency (PCE) of solar cell with a structure of FTO/TiO2/CuaAgm1Bim2In/CuI/carbon reached 2.76%, which is the highest PCE for CuaAgm1Bim2In absorbers.
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 CuaAgm1Bim2In/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 CuaAgm1Bim2In could be reduced from 2.06 to 1.78 eV. Solar cells with the structure of FTO/TiO2/CuaAgm1Bim2In/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.