Ambient Air Deposition Allows Reaching Record Light Use Efficiency in FAPbI₃ Perovskite Solar Cells

Semi-transparent solar cells represent an exciting opportunity for sustainable energy production, thanks to the possibility of being integrated into buildings and urban environments, effectively exploiting the already existing space. Perovskite solar cells (PCSs) are ideal candidates, offering high power conversion efficiencies (PCEs) combined with a tuneable band gap and adjustable thickness, which allow a convenient modulation of the average visible transmittance (AVT). However, balancing high PCE and high AVT is a challenging target. This study uncovers that depositing the perovskite layer based on Formamidinium Lead Iodide (FAPbI₃) thin films in ambient air, rather than in a nitrogen-controlled atmosphere, allows an increase in the AVT value of up to > 40% while also enhancing the photovoltaic performance and stability. The optoelectronic quality of the as-obtained perovskite layer is substantially enhanced, showing fewer defects and a superior morphology. As a result, the air-deposited devices exhibit higher efficiency, which, combines with the enhanced AVT, results in a champion device with a light use efficiency (LUE) of 4.2%, having a PCE of 13.8% and AVT of 30.4%. The record LUE value and the possibility of being deposited in ambient air conditions pave the avenue toward the real-world application of semi-transparent PSCs.