Comprehensive insights into defect passivation and charge dynamics for FA0.8MA0.15Cs0.05PbI2.8Br0.2perovskite solar cells

Abstract

Nonradiative charge recombination is the main restriction on the high efficiency of organic-inorganic hybrid perovskite solar cells (PVSCs). The synergistic manipulation of the grain boundary/interface traps can control charge behavior and improve device performance. In our work, the composition of perovskite used is FA0.8MA0.15Cs0.05PbI2.8Br0.2 (MA is methylammonium, FA is formamidinium), which produces high-performing PVSCs. A trace additive of n-butylammonium bromide (BABr) was incorporated into the perovskite precursor to passivate grain-boundary defects. The NH4Cl/KCl was spin-coated onto the electron-transport layer to modify interface contact and impede nonradiative charge recombination, inducing a high power-conversion efficiency (PCE). The highest-performing PVSCs achieved a PCE of 21.02%, a Voc of 1.13 V, a Jsc of 23.55 mA cm-2, and a FF of 0.79 under a reverse voltage scan (under a forward voltage scan the values were as follows: PCE, 20.13%; Voc, 1.12 V; Jsc, 23.65 mA cm-2; FF, 0.76), with a negligible J-V hysteresis. The hybrid 2D/3D perovskite heterostructure formed through the incorporation of BABr increased crystallinity and mitigated nonradiative recombination, resulting in reduced current-voltage hysteresis, enhanced efficiency, and significantly improved operational stability. With impedance spectroscopy and time-resolved surface photovoltage spectroscopy, the charge dynamics in PVSCs were determined.