Unveiling the humidity effect and achieving an unprecedented 12% PCE in MAPbBr3 solar cells

Fabricating high-efficiency MAPbBr3 solar cells is challenging due to substantial recombination losses within the perovskite layer and at interfaces with charge transport layers. Here, we investigate the critical role of ambient humidity in improving device performance and stability. We varied humidity levels from dry N2 to 80 % relative humidity (RH) and identified that maintaining the environment at 25 % +/- 0.82 % RH optimally enhances the morphological, structural, optical properties of MAPbBr3 films. Our novel analyses demonstrate that this specific humidity level significantly reduces bulk defect densities and interface recombination sites without any additive, leads to the formation of larger crystal grains, and improves optical qualities as well. Consequently, devices fabricated under these conditions achieved the highest device efficiency of 12.14% for the MAPbBr3 solar cells. Additionally, they exhibited remarkable long-term stability, retaining nearly 90 % of the initial efficiency after 1000 h damp-heat and 100 cycles of thermo-cycling tests with encapsulated devices.