Direct Evidence of Ion Diffusion for the Silver‐Electrode‐Induced Thermal Degradation of Inverted Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) have recently demonstrated high efficiencies of over 22%, but the thermal stability is still a major challenge for commercialization. In this work, the thermal degradation process of the inverted structured PSCs induced by the silver electrode is thoroughly investigated. Elemental depth profiles indicate that iodide and methylammonium ions diffuse through the electron‐trasnporting layer and accumulate at the Ag inner surface. The driving force of forming AgI then facilitates the ions extraction. Variations on the morphology and current mapping of the MAPbI3 thin films upon thermal treatment reveal that the loss of ions occurs at the grain boundaries and leads to the reconstruction of grain domains. Consequently, the deteriorated MAPbI3 thin film, the poor electron extraction, and the generation of AgI barrier result in the degradation of efficiencies. These direct evidences provide in‐depth understanding of the effect of thermal stress on the devices, offering both experimental support and theoretical guidance for the improvement on the thermal stability of the inverted PSCs.

Effect of Electron‐Transport Material on Light‐Induced Degradation of Inverted Planar Junction Perovskite Solar Cells

“…Interestingly, the effect is greater in the noncovered regions suggesting that the [60]PCBM layer and/or silver contact slightly protect the device. [33,39,[44][45][46] In both the [60]PCBM and PDI-EH devices, we see the formation of the interfacial AgI layer. The AgI − ion fragment ( Figure S5, Supporting Information) indicates the formation of the interfacial AgI layer, which is fully consistent with the previous findings.…”

Interface Engineering for Highly Efficient and Stable Planar p‐i‐n Perovskite Solar Cells

“…[125] Consequently, the deteriorated MAPbI 3 thin film, the poor electron extraction, and the generation of AgI barrier resulted in the degradation of PVSCs. The introduction of passivation layer at the perovskite/ETM and ETM/metal electrode interfaces could prohibit ion motion to improve the device stability.…”

“…[124] In the work of Wang and co-workers, they clearly demonstrated the reconstruction of grain boundaries caused by ion migration, which may induce defects in both perovskite film and perovskite/PCBM interface. [125] Recently, our group developed a graded 3D-2D perovskite interface with 2D structure passivated grain boundaries. We found that the 2D perovskite could passivate at the surface and grain boundaries of perovskite film which modified the surface energy level and reduced the charge recombination, resulting to an ultrahigh V oc of 1.17 V. And at the same time, the 2D passivated grain boundaries effectively blocked the cross-layer ion diffusion, prevented the migration of I − ion from perovskite layer to PCBM layer, thus dramatically improved the thermal stability of p-i-n PVSC.…”

“…[106][107][108] The ion migration was initially noticed through the anomalous hysteresis in the PVSCs [109] and subsequently found to be more general in explaining phenomena such as light soaking effect [110,111] and halide redistribution. [112] Furthermore, ionic migration has adverse effects on the stability of PVSCs because the migrating iodide ions can react with metal electrodes, [113] resulting in the degradation of PVSCs. Interface engineering is needed to control the ion migration and improve the efficiency and stability of the PVSCs.…”

Goethite Quantum Dots as Multifunctional Additives for Highly Efficient and Stable Perovskite Solar Cells

“…The depth profiles of CN − , I − , and Au − of PSCs functioned with the sputtering time from 0 to 600 s are shown in Figure d,e. The CN − ion is attributed to the existence of CH 3 NH 3 + (MA + ) . For the device without FeOOH QDs (Figure d), I − and CN − remarkably diffused into the Au electrode after 360 h at 85 °C, whereas the diffusion of I − and CN − ions is negligible for device with FeOOH QDs (Figure e).…”