Electron Diffusion\nLength Effect on Direction of Irradiance\nin Transparent FAPbBr<sub>3</sub> Perovskite Solar Cells

Transparent photovoltaics for building integration represent\na\npromising approach for renewable energy deployment. These devices\nrequire transparent electrodes to manage transmittance and to ensure\nproper cell operation. In this study, transparent FAPbBr<sub>3</sub>-based perovskite solar cells optimized via a passivation treatment\nwere demonstrated with average visible transmittance values above\n60% and light utilization efficiencies up to 5.0%. Experiments under\nvarying ultraviolet (UV) irradiance intensities from both front and\nrear directions revealed performance differences correlated with diffusion-limited\ntransport and open-circuit voltage changes. Combining the UV-radiated\nexperiments and drift-diffusion simulations, an asymmetry between\nthe diffusion lengths of electrons and holes in the perovskite is\nrevealed, with estimated values resulting in less than 50 nm and more\nthan 99 nm, respectively. Our methods not only identify electron–hole\ndiffusion length differences but also introduce a general protocol\nfor characterizing solar cells with transparent electrodes.