Non‐Uniform Chemical Corrosion of Metal Electrode of p–i–n Type of Perovskite Solar Cells Caused by the Diffusion of CH₃NH₃I

Abstract

Although perovskite solar cells have shown high power conversion efficiency, performance stability is still insufficient. Herein, the decay kinetics of the p–i–n type of perovskite cells under light illumination is monitored. It is found that the degradation of the performance is mainly caused by the decrease in short‐circuit current (JSC), which is directly related to the loss of active area. Secondary ion mass spectrometry (SIMS) analysis confirms that both CH3NH3+ and I− migrate toward the metal electrode during aging through the thin PC61BM layer. Atomic force microscope (AFM) and scanning electron microscope (SEM) analyses reveal that some part of the PC61BM layer is too thin to cover the rough surface of the perovskite film fully. Therefore, chemical corrosion of the metal electrode by CH3NH3I leads to the loss of active area and the consequent short circuit current is proposed to be the performance decay mechanism of perovskite solar cells, which is further supported by the stability improvement of the cells by inserting a thin bathocuproine (BCP) buffer layer between the metal electrode and PC61BM, where the CH3NH3I migration is blocked by the BCP layer.

Review on Chemical Stability of Lead Halide Perovskite Solar Cells

“…For example, Ma et al . found that both CH 3 NH 3 + and I − can migrate towards the Al electrode through a PC 61 BM layer, resulting in the chemical corrosion of the Al electrode and the degradation of the perovskite film [ 189 ]. In particular, CH 3 NH 3 I is highly acidic and can react with Al as shown below: …”

The effect of perovskite interface contacts on hysteresis behavior in perovskite solar cells

“…However, experimental findings have shown ionic migration transport to ETLs, HTLs, and contact interfaces. 10,11 For this purpose, Calado et al 12 considered ions to be stationary in ETL and HTL. Their results showed changes in the high density of mobile ions, charge collection, and screening of the electric field by ion redistribution in the absorber layer under steady-state conditions.…”

Inhibiting metal-inward diffusion-induced degradation through strong chemical coordination toward stable and efficient inverted perovskite solar cells

“…The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has been rapidly improving in the past decade owing to their tunable bandgap, [1][2][3] high absorption coefficient, [4][5][6] high charge mobility, 7,8 low exciton binding energy, [9][10][11] long carrier diffusion length, [12][13][14] simple process 15,16 and low manufacturing cost. [17][18][19] The PCE of normal (n-i-p) PSCs exceeds 25.5%, 20 while that of inverted PSCs has reached 23.0%.…”