Unravelling the Mechanism of Ionic Fullerene Passivation for Efficient and Stable Methylammonium-Free Perovskite Solar Cells

Abstract

Despite having attractive stability over the volatile methylammonium (MA) cation, double-cation (Cs, FA) perovskite solar cells are largely overlooked because of their inferior performance compared to MA-based devices. Among all the device engineering strategies, surface passivation represents a promising approach to acquire improved performance. However, effective passivation strategies have not yet been developed for attaining efficiencies of MA-free cells close to their theoretical limit. Herein, fullerene passivators with different binding groups are investigated to establish relationships between molecule structure and perovskite surface properties. It is found that surface treatment with bis-fulleropyrrolidium iodide (bFPI) can have strong interaction with charged defects, leading to effective defect passivation and favorable band-bending at the interface. The resulting bFPI-treated device shows significantly reduced defect density as well as accelerated electron extraction from perovskite into the cathode. Consequently, the MA-free device exhibits an efficiency of 21.1% with long-term environmental stability.

Nanoscale Charge Accumulation and Its Effect on Carrier Dynamics in Tri-cation Perovskite Structures

“…Additionally, the surface charge accumulation was accelerated as seen in the extracted fitting time constant in Figure 6 b for steps III and V. These observations are consistent with other studies showing that the addition of PCBM on the perovskite active layer results in passivation of shallow and deep traps. 1 , 49 − 51 The results indicate that the issues of charge accumulation or enhanced ion migration at the GBs can be resolved by appropriate surface passivation. 49 The addition of a thin TiO x top layer results in a clear increase in the rate of charge accumulation and relaxation (steps III and V).…”

Defect mitigation using d-penicillamine for efficient methylammonium-free perovskite solar cells with high operational stability

“…Moreover, Δ E , denoting the difference between the Fermi-level and the CBM of the perovskite, gradually decreased from 0.28 to 0.21 eV for the perovskites without and with PA, respectively, indicative of the increased n-type behavior of the PA-perovskite. 31 The downshifted energy levels and the reduced Δ E are beneficial for electron transfer. Fig.…”

Interfacial Structure and Composition Managements for High‐Performance Methylammonium‐Free Perovskite Solar Cells

“…[ 9 ] This leaves the thermally more stable Rb + , Cs + , and FA + as the preferred cations and I as the favorable halide, which forms the so‐called MA‐free perovskites. [ 12,17 ] Whereas the PSC devices based on the MA‐free perovskites demonstrate better thermostability, their PCEs are inferior to other high‐performance PSCs. [ 12,18,19 ] It is largely attributed to various types of defects formed during film preparations.…”