Energy Barriers Restrict Charge Carrier Motion in MAPI Perovskite Films

Abstract

Understanding of charge trapping processes in halide perovskites is vital to further improve performance of perovskite optoelectronic devices such as solar cells, photodetectors, and LEDs. In this work, transient photocurrent, time‐delayed collection field and transient fluorescence techniques along with numerical simulations are combined to address charge carrier trapping processes during their lateral motion in prototypical methylammonium lead iodide perovskite films formed on interdigitated electrodes. Carrier mobility decreases on hundreds of ns timescale, and its rate depends on the motion character—it is faster when charge carriers drift in the electric field and slower when the motion is caused by diffusion only. This difference becomes particularly evident at low temperatures. Based on the time‐delayed collection field data and carrier motion modelling results, it is demonstrated that the rapid mobility decay at low temperatures is mainly caused by the energy barriers, most likely formed at crystallite boundaries. Even though these barriers are surmountable at room temperature, they still play a major role in determining carrier mobility and diffusion rates. Suggested concept of the potential barriers moves beyond the conventional understanding of carrier mobility, diffusion, and recombination processes in hybrid perovskites.

Double Charge Transfer Dominates in Carrier Localization in Low Bandgap Sites of Heterogeneous Lead Halide Perovskites

“…On the other hand, sample cooling, as we demonstrate, may change these transfer rates, leading to a situation when transfer of the second charge becomes much slower, or transfer of both charge carriers becomes significantly hindered at very low temperatures (see Figure 6), thus enabling observation of the charge separated state by means of time‐resolved PL and TA techniques. We have recently demonstrated that sample cooling causes dramatic photocurrent changes in conventional 3D MAPI films [ 42 ] indicating that energy barriers formed between perovskite grains play an important role in carrier migration. Thus, the presence of energy barriers between perovskite domains, which may be different for electrons and holes, is not surprising.…”

Tuning the Structural Isomers of Phenylenediammonium Cations to Afford Efficient and Stable Perovskite Solar Cells and Modules

“…We also used low excitation intensity, when carrier recombination could be ignored. In these conditions, the photocurrent kinetics on a sub-microsecond time scale was mainly determined by the carrier trapping and by the hole extraction to hole transport layer (HTL) 39 . The control device with HTL shows faster photocurrent decay than that without HTL during initial ~ 50 ns due to the hole extraction (Fig.…”

Suppression of Electron Trapping in MAPbI3 Perovskite by Sr2+ Doping

“…Acceleration of the PL decay at pulsed excitation fluencies, similar to our study, was shown to be mainly determined by the electron trapping. [21,22] Therefore, we assume that the incorporation of a small amount of Sr 2þ additives (≤0.4%) prolonging the second decay component reduces the electron trapping rate.…”

“…We have recently demonstrated that such barriers almost completely hinder carrier motion at low temperatures and also reduce their motion rate at room temperature. [22] Therefore, to clarify the influence of Sr 2þ additives on the charge carrier recombination, we performed TDCF investigations, which are commonly used for this task, because it enables separation between recombination and other dynamic processes. [22,23] Briefly, in TDCF measurements, we excite the sample at zero electric field and apply the electric field after a variable delay and measure the total extracted charge as a function of the delay time.…”

“…[22] Therefore, to clarify the influence of Sr 2þ additives on the charge carrier recombination, we performed TDCF investigations, which are commonly used for this task, because it enables separation between recombination and other dynamic processes. [22,23] Briefly, in TDCF measurements, we excite the sample at zero electric field and apply the electric field after a variable delay and measure the total extracted charge as a function of the delay time. The extracted charge is directly proportional to the total number of charge carriers, including trapped ones, present in the sample at some particular delay.…”