Ab initio study of the moisture stability of lead iodine perovskites

Abstract

The stability of hybrid lead iodine perovskite in a humid environment has been a major obstacle to developing long-term photovoltaic devices. However, understanding the detailed degradation mechanism of lead iodine perovskite in moisture is still challenging. Herein, using first-principles calculations, we show that embedded water molecules will facilitate the decomposition of lead iodine perovskite. Alloying FAPbI and CsPbI to form mixed-cation lead iodine perovskites not only can optimize the tolerance factor to obtain better phase stability, but also can improve the moisture stability of them. With the accumulation of water molecules in the perovskite lattice, the optical absorption spectra show a blue-shift and decreased intensity, and the moisture stabilities of lead iodine perovskites are further lowered. The iodine vacancy in lead iodine perovskites can facilitate the water molecule migration and thus is a disadvantage in improving the moisture stability of them, which should be minimized during perovskite growth. These findings provide new insight in understanding the poor moisture stability of lead iodine perovskites, which should be helpful for the future design and optimization of stable perovskite solar cells.

Tin Halide Perovskites: Progress and Challenges

“…In spite of their interesting characteristics, the presence of Pb in halide perovskites has been a drawback due to toxicity and moisture sensitivity. [10,11,23,24,237] The degradation of perovskites by factors such as moisture, [238,239] light, [240] heat, [241] and oxygen [242,243] following a variety of mechanisms which include; polymorphic transformation, [244] hydration, [245] ion diffusion, [246] decomposition, [247] oxidation, [248] etc., poses immense environmental concerns in the PV research community. This has led to the proposal of Sn as a benign alternative to Pb in perovskite materials.…”

Toward stable lead halide perovskite solar cells: A knob on the A/X sites components

“…The band structures of (E) MAPbI 3 and (F) MAPbI 3 with four-absorbed H 2 O molecules in on supercell. Credit adapted from ( He et al., 2018 ). Deep-level transient spectroscopy (DLTS) spectra with different various bias voltage for the deep-level defects of (G) fresh and (H) aged (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 .…”

“…Besides, the I ‒ vacancy, the most common point defect in MAPbI 3 perovskite could facilitate the migration and reduced diffusion barrier of H 2 O ( He et al., 2018 ). The near-gap electronic states show significant changes after introducing H 2 O in the lattice, resulting in an increased band gap (from 1.55 eV to 1.84 eV) accordingly ( Figures 3 E and 3F).…”

Reviewing and understanding the stability mechanism of halide perovskite solar cells

“…The easy adsorption and lower activation barrier explain well why water reacts so strongly with halide perovskite in experiments. In addition, He et al also found that the interstitial water molecule will accelerate decomposition of halide perovskites, 67 and the surface water molecule will replace MA cations with surface halide by forming hydrogen bonds. 68 To avoid degradation in hydration process, using lowsensitivity material is a suitable approach.…”