Solar Degradation and Stability of Lead-Free Light Absorber Cs2AgBiBr6 in Ambient Conditions

As numerous studies on highly efficient perovskite solar cells have been conducted on lead-based light absorbers, such as MAPbI(3) and FAPbI(3), increasing concerns are rising regarding toxicity and stability issues. One of the most prominent and promising lead-free alternatives is the double-perovskite Cs2AgBiBr6, which is well-suited for multi-junction solar cells considering its relatively large indirect bandgap of around 1.95-2.05 eV. Despite distinctive reports on its performance under ambient conditions, the demonstrated stability has not yet been conclusively clarified. Within this study, the degradation behavior of Cs2AgBiBr6 single crystals is investigated under different ambient environments, such as AM1.5g solar irradiation, aquatic conditions, and humidity. The corresponding samples are analyzed by using Raman, UV-vis, energy-dispersive X-Ray, and micro-photoluminescence spectroscopies together with X-Ray diffraction. High intrinsic stability of Cs2AgBiBr6 in ambient conditions and severe degradation in aquatic conditions are observed. Furthermore, surface morphology alterations are found during the simulated solar irradiation indicating photo-accelerated degradation behavior. In the results of this study, it is clearly implied that intense research efforts need to be put into sealing the Cs2AgBiBr6 layer in solar cells with the goal of protecting it from humidity and water intrusion simultaneously, therefore avoiding photo-accelerated degradation.