Water Infiltration in Methylammonium Lead Iodide Perovskite: Fast and Inconspicuous

Abstract

While the susceptibility of CH 3 NH 3 PbI 3 to water is well-documented, the influence of water on device performance is not well-understood. Herein, we use infrared spectroscopy to show that water infiltration into CH 3 NH 3 PbI 3 occurs much faster and at a humidity much lower than previously thought. We propose a molecular model in which water molecules have a strong effect on the hydrogen bonding between the methylammonium cations and the Pb−I cage. Furthermore, the exposure of CH 3 NH 3 PbI 3 to the ambient environment increases the photocurrent of films in lateral devices by more than 1 order of magnitude. The observed slow component in the photocurrent buildup indicates that the effect is associated with enhanced proton conduction when light is combined with water and oxygen exposure.

Temperature-dependent optical spectra of single-crystal (CH3NH3)PbBr3 cleaved in ultrahigh vacuum

“…Experimental data and their interpretation, however, show strong variations. Spectroscopic results obtained from thin films depend on growth technique [29][30][31][32][33], grain size [30,34], and environmental conditions [35,36].…”

Formation criteria of high efficiency perovskite solar cells under ambient conditions

“…Several authors have described the effect of water during degradation of perovskite solar cells. 6,[17][18][19][20] It has been reported that water in the gas phase rapidly diffuses in perovskite films to generate hydrates via a two-step process starting with formation of MAPbI 3 ·H 2 O followed by (MA) 2 PbI 6 ·H 2 O after prolonged exposure to moisture. 17 A perfect understanding on the actual role of water during crystallization of the perovskite layer has been more elusive due to the high complexity of the system.…”

Reversible air-induced optical and electrical modulation of methylammonium lead bromide (MAPbBr3) single crystals

“…For instance, M€ uller and co-workers showed that the reversible water infiltration into MAPbI 3 thin films occurs fast at a low relative humidity and increases the ionic conductivity remarkably. 40 Galisteo-Lopez et al reported that the photoluminescence (PL) of perovskites is better in oxygen rather than nitrogen conditions. 41 Similarly, Fang and coworkers showed a PL variation of MAPbBr 3 single crystals (MSCs) by exposing them to different gases.…”

“…Specifically, those shallow trap states, caused by the reversible air (mainly O 2 and H 2 O) infiltration into MSCs, 40 could increase the PL but decrease the photocurrent of perovskite devices. Using first-principles computational analysis, several possible defect models are presented and verified according to the optical, electrical, and XRD results.…”