Ionic additive engineering for stable planar perovskite solar cells with efficiency >22%

Abstract

High crystallization quality and low defect state density of perovskite films are essential for high-performance devices. Herein, we develop a facile and effective method using potassium hexafluorophosphate (KPF6) to fabricate perovskite solar cells (PSCs) with highly improved power conversion efficiency (PCE) and outstanding stability. The corresponding mechanisms of the improved crystallization process, grain boundaries (GBs) passivation, and internal ionic defect passivation of the perovskite films are systematically studied. The results indicate that the introduced PF6− can promote crystallization by increasing fully coordinated intermediate groups in the perovskite solution and compensate for halide vacancies, which can modify ionic point defects in the perovskite films, resulting in reduced non-radiative recombination. Meanwhile, K+ ions are predominantly distributed at the GBs, which not only benefits the device efficiency but also significantly reduces the hysteresis due to the passivation effect. The champion passivated device presents a PCE of 22.04%, with a significantly improved PCE of around 16% compared with that of the control device (18.99%), retaining 80% of its initial PCE after 1000 h of light soaking without any encapsulation. Our work provides a defect passivation method for further improving both the PCE and stability of PSCs and can also be extended to other devices.