High Light Utilization and Color Rendering in Vacuum‐Deposited Semitransparent Perovskite Solar Cells

Formamidinium lead iodide perovskite compositions have a low open circuit voltage deficit and thus a higher power conversion efficiency (PCE) potential. However, their low bandgap makes it difficult to achieve a semitransparent perovskite solar cell (ST-PSC) with a high average visible transmittance (AVT) and thus, a high light utilization efficiency (LUE). Attaining a high AVT in such low bandgap perovskite‑based semitransparent solar cells requires the perovskite layer to be very thin (thickness < ≈100 nm) and the rear electrode to be made of a transparent conductive oxide. Moreover, both the front and rear electrodes should exhibit minimal reflectance losses. In this work, meeting these requirements, fully vacuum-deposited, low bandgap (≈1.55 eV, ≈100 nm thick) semitransparent perovskite solar cells are fabricated that demonstrate a high LUE value of 4.2 (PCE: 9.26% and AVT: 45.3%). Additionally, a high color rendering index of 82.4 along with a high AVT of ≈48.5% is achieved in a ST-PSC via modulation of the device reflectance by tuning both the perovskite layer thickness and the rear electrode stack. The ST‑PSCs retained > 90% of their efficiency for >1000 h when thermally stressed at 85 °C in N2 atmosphere.