Ambient and green processing of lead-free double perovskite Cs2AgBiBr6 films

Abstract

Lead-free inorganic perovskite Cs₂AgBiBr₆ has emerged as a promising alternative to lead-based halide perovskites (LHPs), addressing concerns over toxicity and stability. However, fabricating high-quality Cs₂AgBiBr₆ films remains significantly more challenging than LHPs. Here, we investigate the impact of processing environments on film morphology, comparing deposition in ambient air and under a nitrogen environment. We find that moisture levels play a critical role in determining Cs₂AgBiBr₆ film quality, with significant differences observed between the controlled glovebox environment (∼1 ppm moisture) and ambient air with a relative humidity of 60–70%. Pristine films processed in ambient air show large aggregates and poor surface coverage, whereas dense and uniform films are achieved in a nitrogen glovebox. However, achieving cost-effective and scalable manufacturing requires ambient processing methods. To overcome this challenge, we introduce an ethyl acetate (EA) antisolvent treatment that enables the ambient deposition of dense and uniform Cs₂AgBiBr₆ films, even at a high relative humidity (60–70%). This approach enhances film morphology, crystallinity, and device performance, leading to a five-fold improvement in power conversion efficiency (PCE). EA-treated films achieving a PCE of 1.08%, compared to 0.21% for pristine films are reported. Recognizing the importance of solvent toxicity in ambient and scalable production, we assess the environmental impact using the CHEM21 framework, finding both the precursor solvent and antisolvent in this work to be environmentally favorable. Our findings offer a green, simple, and ambient fabrication strategy for high-quality, lead-free Cs₂AgBiBr₆ films, advancing their potential for future optoelectronic applications such as solar cells, photodetectors, and memristors.