Role of Ionic Functional Groups on Ion Transport at Perovskite Interfaces

Abstract

Hybrid organic/inorganic perovskite solar cells are invigorating the photovoltaic community due to their remarkable properties and efficiency. However, many perovskite solar cells show an undesirable current-voltage (I-V) hysteresis in their forward and reverse voltage scans, working to the detriment of device characterization and performance. This hysteresis likely arises from slow ion migration in the bulk perovskite active layer to interfaces which may induce charge trapping. We show that interfacial chemistry between the perovskite and charge transport layer plays a critical role in ion transport and I-V hysteresis in perovskite-based devices. Specifically, phenylene vinylene polymers containing cationic, zwitterionic, or anionic pendent groups were utilized to fabricate charge transport layers with specific interfacial ionic functionalities. The interfacial-adsorbing boundary induced by the zwitterionic polymer in contact with the perovskite increases the local ion concentration, which is responsible for the observed I-V hysteresis. Moreover, the ion adsorbing properties of this interface was exploited for perovskite-based memristors. This fundamental study of I-V hysteresis in perovskite-based devices introduces a new mechanism for inducing memristor behavior by interfacial ion adsorption.

A Biopolymer Heparin Sodium Interlayer Anchoring TiO2 and MAPbI3 Enhances Trap Passivation and Device Stability in Perovskite Solar Cells

“…The extracted slope in the V oc versus P light characteristics amounts to 1.75 and 1.35 k B T / q for devices without and with HS, respectively. That the reduced slope approaches the unity in HS device affirms the suppressed SRH recombination with effective traps passivation, which agrees with the PL results.…”

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

“…By measuring the local photocurrents curves using C‐AFM at the grain boundary and on the grain domain, it is shown that the J – V hysteresis only observed in curves at the grain boundaries . C‐AFM study also shows that the interfacial chemistry between the perovskite and charge transport layer plays a critical role in the ion transport and I – V hysteresis in perovskite‐based devices . Using KPFM, band bending at grain boundaries has also been reported by different researchers .…”

The Origin of Photoinduced Capacitance in Perovskite Solar Cells: Beyond Ionic‐to‐Electronic Current Amplification

“…Impedance spectroscopy is widely used to analyze the trap distribution in PVSK solar cells. [ 7–11 ] These analyses presuppose that the capacitance in the low‐frequency range is only affected by the chemical capacitance of PVSK. However, impedance spectra for unipolar injection devices demonstrate that the capacitance of PVSK is obviously affected by the ionic‐to‐electronic current amplification.…”

“…In the same context, impedance spectroscopy has been applied to investigate halide perovskites (PVSKs), which have rapidly become one of the most attractive materials in the photovoltaic community, with the primary objective of analyzing the trap distribution in PVSK solar cells. [ 5–12 ] However, careful consideration is necessary to analyze the impedance of PVSK solar cells because PVSKs exhibit high ionic conductivity, which affects their electrical responses during impedance spectroscopy measurements.…”