Crystalline Clear or Not: Beneficial and Harmful Effects of Water in Perovskite Solar Cells

Abstract

Clarification of how water affects the photovoltaic performance of perovskite solar cells is one of the major challenges to successfully develop a large-scale low-cost fabrication process. Many authors have reported beneficial effects of moisture during the fabrication of perovskite solar cells (PSCs), such as enhanced crystallinity, photoluminescence and photovoltage. However, the highest power conversion efficiency reported until this date was obtained under completely dry atmosphere conditions, avoiding the presence of water during perovskite formulation and preserving the damage caused by moisture exposure with encapsulation techniques. This apparent contradiction makes patent the necessity of an extensive clarification to establish the conditions in which water represents a beneficial or harmful factor in the development of high efficiency and stable perovskite devices. In this review, we summarized the effects of water, both as an additive into the perovskite formulation as an additive and as moisture exposure during fabrication. We discuss in depth the structural and chemical effects, analysing also the photovoltaic consequences during operation conditions. As a final input, we remark a useful method to perform high efficiency PSCs under different lab ambient conditions and highlight the latest advances in hydrophobic devices and encapsulation techniques.

Eppur si Muove: Proton Diffusion in Halide Perovskite Single Crystals

“…It has been observed multiple times that exposure to small amounts of water [51][52][53] or methylamine [33] (both creating proton vacancies in the material), enhance the performance of HaP PV cells. The mechanism of this enhancement has been attributed solely to recrystallization.…”

“…Summarizing, the positive effects of water [ 51–53 ] and light‐soaking, on the perovskite, [ 73–76 ] which were also reported a few times for devices, can be traced to water extracting H + from CH 3 NH 3 + , serving as catalyst for, and light speeding up H + migration HaPs. Further experiments are needed to check this view and the details of the mechanism(s) involved.…”

Quantum dot-modified titanium dioxide nanoparticles as an energy-band tunable electron-transporting layer for open air-fabricated planar perovskite solar cells

“…Open-air atmosphere containing moisture (RH approximately 50% in this work) and oxygen causes the degradation of perovskite absorber (MAPbI 3 ) films to form PbI 2 and MAI, because of high polarity of H 2 O. 16,17,51 Normally, in the perovskite composition, PbI À 3 anion cooperates with CH 3 NH þ 3 cation by hydrogen bond between H-C/I À and H-N/I À . When the perovskite film interacts with H 2 O, the hydrogen bond (O-H/I À and O/N-H) can be generated.…”

“…Besides highly efficient performance, perovskite solar cells are still facing a poor stability issue, where rapid degradation occurs under high humidity environments. 16,17 Several works reported the perovskite cells with relatively small areas fabricated under nitrogen (N 2 ) atmosphere. For example, high efficiency of perovskite solar cells of approximately 23% (with the active area of approximately 0.09 cm 2 ) was reported by Jeon et al 18 Anaraki et al developed the efficient performance of planar perovskite solar cells with PCE closed to 20% with an active area of 0.16 cm 2 .…”

“…Besides highly efficient performance, perovskite solar cells are still facing a poor stability issue, where rapid degradation occurs under high humidity environments. 16,17…”