Growing high-quality CsPbBr3 by using porous CsPb2Br5 as an intermediate: a promising light absorber in carbon-based perovskite solar cells

Abstract

CsPbBr₃ with a large band gap (∼2.3 eV) is a promising material for fabricating perovskite solar cells (PSCs) with a high open-circuit voltage (V_oc) and high stability. However, a suitable method is still lacking for depositing high-quality CsPbBr₃ films. Herein, we develop a novel strategy to deposit high-quality CsPbBr₃ films by employing a porous CsPb₂Br₅ film as an intermediate layer. Highly porous CsPb₂Br₅ films composed of lamellar crystals were obtained by immersing Pb–Br precursor layers in a low-concentration CsBr IPA solution. The low CsBr concentration helped to widen the processing window of CsPb₂Br₅, while the low-polarity IPA solvent served to keep the film structure stable during the reaction. High-quality CsPbBr₃ films with full coverage, high purity and low defect density were obtained by further converting the CsPb₂Br₅ films in a high-concentration CsBr solution. After introducing the optimized CsPbBr₃ film into a carbon-based PSC without a hole transporting material (C-PSC), a power conversion efficiency (PCE) of 6.1% and a V_oc of 1.38 V were achieved. Moreover, the devices without encapsulation show almost no PCE decay after 200 days of storage in ambient air (25–85% relative humidity, 20–30 °C) and at 80 °C (10–20% relative humidity) for over 1080 h.