Fluoroaromatic Cation-Assisted Planar Junction Perovskite Solar Cells with Improved VOC and Stability: The Role of Fluorination Position

The notoriously poor stability of organic-inorganic hybrid perovskite solar cells is a crucial issue restricting the commercial application of such burgeoning technology. Passivation of bulk perovskite absorber by fluorinated aromatic ammonium salt via low-dimensional perovskites has been proved to be an effective way of improving stability and efficiency. Herein, the influence of fluorination position (ortho-, meso-, and para-) on the aromatic moiety is studied in terms of their dipole moments and the ability to reduce defect density, extend carrier lifetimes, and assist charge transfer. In addition to the improved power conversion efficiency (PCE) from 19.17% to above 20%, the device treated with 2-(o-fluorophenyl)ethylamine iodide exhibits a remarkable open-circuit voltage (V-OC) of 1.21 V. While the 2-(p-fluorophenyl)ethylamine iodide-treated device shows only 1% loss of its initial value under ambient atmosphere (with RH of 10-30%) without encapsulation for 1440 h storage. The molecular structure of fluorinated aromatic cations plays multiple roles in passivating the interface of the perovskite device.