Discerning recombination mechanisms and ideality factors through impedance analysis of high-efficiency perovskite solar cells

Abstract The ubiquitous hysteresis in the current-voltage characteristic of perovskite solar cells (PSCs) interferes in a proper determination of the diode ideality factor ( n ), a key parameter commonly adopted to analyze recombination mechanisms. An alternative way of determining n is by measuring the voltage variation of the ac resistances in conditions of negligible steady-state dc currents. A reliable analysis of n based on the determination of the resistive response, free of hysteretic influences, reveals two separated voltage exponential dependences using different perovskite absorbers (3D perovskites layer based on CH 3 NH 3 PbI 3 or mixed Cs 0.1 FA 0.74 MA 0.13 PbI 2.48 Br 0.39 ) and a variety of interlayers (2D perovskite thin capping). The dominant resistive element always exhibits an exponential dependence with factor n ≈ 2 , irrespective of the type of perovskite and capping layers. In addition, a non-negligible resistive mechanism occurs at low-frequencies (with voltage-independent time constant ~ 1 s) which is related to the kinetic properties of the outer interfaces, with varying ideality factor ( n = 2 for CH 3 NH 3 PbI 3 , and n = 1.5 for Cs 0.1 FA 0.74 MA 0.13 PbI 2.48 Br 0.39 ). Our work identifies common features in the carrier recombination mechanisms among different types of high-efficiency PSCs, and simultaneously signals particularities on specific architectures, mostly in the carrier dynamics at outer interfaces.