Improving UV stability of MAPbI3 perovskite thin films by bromide incorporation

Highlights: • CH₃NH₃Pb(I_1-xBr_x)₃ perovskite films were prepared using spin coating technique. • The effect of UV irradiation on CH₃NH₃Pb(I_1-xBr_x)₃ was studied. • CH₃NH₃Pb(I_1-xBr_x)₃ films with more than 20% of Br exhibit a good UV stability. • Detailed structural and optical characterization are reported. Despite the astonishing progress reached in the last five years, perovskite films still lack some stability. It is well known that UV light and humidity affect strongly perovskite-based solar cell performances. We herein investigate the degradation process of perovskite-based CH₃NH₃PbI₃ thin films without encapsulation in presence of direct UV light. The UV irradiation effect on structural, morphological and optical properties of the perovskite thin film is studied. Experimental results show significant degradation of perovskite properties after 12 h of exposure to UV light. The main objective of this work is to show that it is possible to improve the MAPbI₃ stability upon UV by the adequate incorporation of the bromide atoms in the perovskite matrix. In fact, it has been found that the CH₃NH₃Pb(I_1-xBr_x)₃ perovskite exhibits a better stability, distinctly when the bromide fraction is above 20%. We believe that the observed improvement is linked to the structural transition from the tetragonal phase to the more stable cubic structure as shown by the XRD results.