Pinning Down the Anomalous Light Soaking Effect toward High-Performance and Fast-Response Perovskite Solar Cells: The Ion-Migration-Induced Charge Accumulation

Abstract

The light soaking effect (LSE) is widely known in perovskite solar cells (PVSCs), but its origin is still elusive. In this study, we show that in common with hysteresis, the LSE is owed to the ion migration in PVSCs. Driven by the photovoltage, the mobile ions in the perovskite materials (MA/I) migrate to the selective contacts, forming a boosted P-i-N junction resulting in enhanced charge separation. Besides, the mobile ions (MA) can soften and suture the PCBM/perovskite interface and thus reduce the trap density, in keeping with a higher open-circuit voltage. Finally, almost LSE-free PVSCs can be prepared by using 0.1 wt % MAI-doped PCBM as the electron transport material, whereas overdoping (1 wt % MAI doping) makes the LSE even more pronounced due to excess mobile ions that need time to migrate to reach a new quasi-static state.

Ion Migration: A “Double‐Edged Sword” for Halide‐Perovskite‐Based Electronic Devices

“…They suggested the “mobile ions” (MA + /V I− , I − /V MA+ ) in the perovskite materials can migrate to the selective electrode assisted by the photovoltage (Figure c,d), resulting in a benign P–I–N junction. This light induced “mobile ion” redistribution has also been reported by Deng et al and confirmed by our group using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) . We also demonstrated that the mobile MA + aggregated near the electron transport layer (ETL) could heal the interfacial deep defects (Figure b) and improve the photocarrier collection, in line with the proposal of Zhao et al…”

“…b) PDS characterization of the PCBM/perovskite and 0.1 wt% MAI‐doped PCBM/perovskite films, indicating a smaller energy disorder in MAI‐doped PCBM. Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…Yuan et al undertook photothermal induced resonance (PTIR) study and observed the long‐range MA + migration in HOIP devices . Zhang et al studied the “ion migration” in high performance PVSCs using TOF‐SIMS and found that this “ion migration” direction could be tuned by light illumination and external bias . Next, where are they accumulated?…”

“…The ion accumulation near device interfaces has also been held responsible for the poor stability of the perovskite devices . Ironically, the ion migration process was also found to promote the performance of perovskite devices under continuous light illumination . Moreover, ion migration has found important application in perovskite resistance‐switching memory devices .…”

Optical Properties of Thin-Film Hybrid Organic-Inorganic Perovskites Under the Influence of Pyridine Vapor

“…To obtain the perovskite film CH 3 NH 3 PbI 3 , the methyl ammonium iodide salt CH 3 NH 3 I was synthesized [13]. The synthesis was carried out by the interaction of methylamine CH 3 The substance crystallizes by removing the solvent in a vacuum rotary evaporator.…”