Precursor engineering for high-quality Cs2AgBiBr6 films toward efficient lead-free double perovskite solar cells

Recently, lead-free double perovskites of Cs2AgBiBr6 have attracted worldwide attention as a promising candidate for eco-friendly photovoltaics because of their intrinsic environmental stability and highly desired low toxicity in comparison with conventional lead halide counterparts. However, their power conversion efficiency (PCE) is still far lower than that of lead halide perovskites, which is mainly associated with their poor quality films. Herein, we report a facile process via precursor engineering based on the BiBr3(DMSO)2 adduct solution to produce high-coverage and smooth Cs2AgBiBr6 films with large grains. As a result, the as-constructed planar solar cells deliver a champion PCE of 0.73%, which exhibits an enhancement of over 40% in PCE compared to that of the control sample, suggesting their potential to be applied in lead-free bismuth-based optoelectronic devices.