Quantification of light-enhanced ionic transport in lead iodide perovskite thin films and its solar cell applications

Abstract

Ionic transport in organometal halide perovskites is of vital importance because it dominates anomalous phenomena in perovskite solar cells, from hysteresis to switchable photovoltaic effects. However, excited state ionic transport under illumination has remained elusive, although it is essential for understanding the unusual light-induced effects (light-induced self-poling, photo-induced halide segregation and slow photoconductivity response) in organometal halide perovskites for optoelectronic applications. Here, we quantitatively demonstrate light-enhanced ionic transport in CH3NH3PbI3 over a wide temperature range of 17–295 K, which reveals a reduction in ionic transport activation energy by approximately a factor of five (from 0.82 to 0.15 eV) under illumination. The pure ionic conductance is obtained by separating it from the electronic contribution in cryogenic galvanostatic and voltage-current measurements. On the basis of these findings, we design a novel light-assisted method of catalyzing ionic interdiffusion between CH3NH3I and PbI2 stacking layers in sequential deposition perovskite synthesis. X-ray diffraction patterns indicate a significant reduction of PbI2 residue in the optimized CH3NH3PbI3 thin film produced via light-assisted sequential deposition, and the resulting solar cell efficiency is increased by over 100% (7.5%–15.7%) with little PbI2 residue. This new method enables fine control of the reaction depth in perovskite synthesis and, in turn, supports light-enhanced ionic transport.

Oxide Layer Enhances Photocurrent Gain of the Planar MAPbI3 Photodetector

“…To the best of our knowledge responsivities of detectors with Cr and Pt/TiO 2 electrodes are among the best reported for the planar MAPbI 3 polycrystalline perovskite detectors. Very similar slow processes were also observed in MAPbI 3 perovskites attributing them to the ion migration, which may create large interface charges [26] and probably additional trapping states. [15] We have investigated photocurrent kinetics upon photoexcitation of the devices with short (0.5 ns) laser pulses as well as with tens of milliseconds rectangular light pulses (see the Supporting Information for more details).…”

The Nature of Ion Conduction in Methylammonium Lead Iodide: A Multimethod Approach

“…[14] and confirmed by ar ecent publication. [38] At the moment, however, we do not have conclusive evidence on the nature of the conductive species under illumination.…”

“…[36,37] There is an urgent need to clarify this point, not only regarding device performance and understanding but also because conditioning of these compounds through stoichiometry control or doping depends crucially on the nature and effective charge of the relevant ionic charge carriers.I nt his respect, understanding equilibrium conditions is aprerequisite to analyze the situation under illumination, therefore in this paper we refer to dark conditions.I nterestingly,a sa lready mentioned in Refs. [14,38],i onic conductivity in these compounds seems heavily influenced by light, an issue that deserves more detailed studies. [39] 3 ,ifthe iodine partial pressure is not extremely small.…”

Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination

“…Taking into account the long diffusion length and low defect trapping in single crystal perovskite, it is expected that significantly higher density of charge carriers is presented at the edges, as the crystal edges serve as a dam of diffusing carriers under continuous illumination. Excessive charge carriers at the edges result in a higher density of phonons and higher potential energy in the lattices . Therefore, it is expected to have a higher possibility to activate the halide ions from lattice into interstitials and vacancies.…”