Impact of Moisture on Photoexcited Charge Carrier Dynamics in Methylammonium Lead Halide Perovskites

Abstract

Organic−inorganic metal halide perovskites are notoriously unstable in humid environments. While many studies have revealed the morphology and crystal structure changes that accompany exposure to humidity, little is known about changes to the photophysics that accompany the degradation process. By combining in situ steady-state and time-resolved photoluminescence with Hall effect measurements, we examined the changes in the photoexcited carrier dynamics for methylammonium lead iodide (MAPbI 3 ) and bromide (MAPbBr 3 ) films exposed to nitrogen gas containing water vapor at 80% relative humidity. The changes in the photophysics of MAPbI 3 interacting with water follow a four-stage process, consisting of surface passivation, free electron doping, interfacial hydration, and bulk hydration. In contrast, MAPbBr 3 exhibits only features associated with the first two stages, which occur at a faster rate.Our results elucidate the degradation mechanisms of perovskite films in high humidity from the perspective of the photophysics, providing insights for how humidity affects the stability of the perovskite materials.

Mechanistic Insights into Photochemical Reactions on CH3NH3PbBr3 Perovskite Nanoparticles from Single‐Particle Photoluminescence Spectroscopy

“…[10] Subsequently, the long-term durability of the perovskite layer remains a concern because of the intrinsic structural instability of the perovskite in ambient air. [11] Moreover, the degradation of the perovskite layer is significantly driven by external factors such as heat, [12] light, [13] moisture, [14] oxygen, [15] and electrical bias. [16] Since several types of defects play crucial roles in most of these behaviors, and a further mechanistic understanding of the defect-related carrier dynamics is necessary for improving the performance and durability of the perovskite devices.…”

Solution‐Processed High‐Quality Cesium Lead Bromine Perovskite Photodetectors with High Detectivity for Application in Visible Light Communication

“…The PD shows a highly linear power response when the incident optical power increases by one order of magnitude. Moreover, the photocurrent/dark current ratio is calculated with the largest value of 1.5 × 10 6 , which is higher than the reported values of perovskite thin‐film PDs (≈10 5 ) and comparable to that of the perovskite single crystal PDs (≈10 6 ) 11,12,15,28,30,32,34. The detailed comparison is presented in Table S2 (Supporting Information).…”

“…To further explore the carrier lifetime of the perovskite composite films, the time‐resolved photoluminescence (TRPL) decays of these films on glass substrates were measured, and the results are presented in Figure 2c. Since no charge transport occurs at the perovskite film interfaces, the charge carrier recombination is closely related to the intralayer photoexcited charge carrier dynamics,30 which is strongly dependent on the intergrain recombination at the grain boundaries. A longer carrier lifetime is most likely related to a lower trap state density at grain boundaries with a lower intralayer recombination rate in the perovskite film 31–33.…”

Giant Humidity Effect on Hybrid Halide Perovskite Microstripes: Reversibility and Sensing Mechanism

“…The photo inactivity at very high humidity levels can be attributed to accelerated recombination of photogenerated carriers. 25 Within the present experimental conditions, to obtain best optoelectronic performance, perovskite devices should be encapsulated or operated at humidity levels lower than 33% RH. A response time (for the signal to increase from 10% to 90%) and recovery time (for the signal to decrease from 90% to 10%) of 100 ms and 500 ms, respectively, were recorded for the perovskite sensor (Figure 2g).…”