Treating CsPbI3 Perovskite with Pyrrolidinium Iodide to Improve the Performance of Perovskite Solar Cells

All-inorganic CsPbI 3 perovskite has attracted wide attention due to its desirable optical bandgap ( E g : ∼1.7 eV) as well as high chemical stability. Nevertheless, the photovoltaic performance of CsPbI 3 perovskite solar cells (PSCs) was limited by severe nonradiative charge recombination due to high defect density at the grain boundary and surface of perovskite films. To address this issue, a pyrrolidinium iodide (PyI) molecule was introduced to modify the surface and grain boundary of CsPbI 3 perovskite films to passivate defects, which improves the quality of CsPbI 3 perovskite films as well as induces the generation of a quasi-2D Py 2 CsPb 2 I 7 capping layer between perovskite layer and hole transport layer. Such quasi-2D Py 2 CsPb 2 I 7 capping layer optimizes interface contact between CsPbI 3 perovskite layer and hole transport layer and blocks the electron transfer from CsPbI 3 perovskite photoactive layer to the hole transport layer. As a result, the performance of CsPbI 3 PSCs is well improved to 17.87% for power conversion efficiency (PCE) with an ultra-high fill factor (FF) of 0.84. In addition, the PyI molecule modified CsPbI 3 perovskite devices exhibit excellent stability, which remains its initial PCE almost unchanged after aging for 35 days under the dry air atmosphere (temperature: 20°C–30°C, control relative humidity (RH): <10%).