The impact of water on the lifecycle of PSCs and the underlying mechanisms in perovskites and PSCs are systematically reviewed.

Halide perovskites with reduced-dimensionality (e.g., quasi-2D, Q-2D) have promising stability while retaining their high performance as compared to their three-dimensional counterpart. Generally, they are obtained in (A)(A)PbI thin films by adjusting A site cations, however, the underlying crystallization kinetics mechanism is less explored. In this manuscript, we employed ternary cations halides perovskite (BA)(MA,FA)PbI Q-2D perovskites as an archetypal model, to understand the principles that link the crystal orientation to the carrier behavior in the polycrystalline film. We reveal that appropriate FA incorporation can effectively control the perovskite crystallization kinetics, which reduces nonradiative recombination centers to acquire high-quality films with a limited nonorientated phase. We further developed an in situ photoluminescence technique to observe that the Q-2D phase (n = 2, 3, 4) was formed first followed by the generation of n = ∞ perovskite in Q-2D perovskites. These findings substantially benefit the understanding of doping behavior in Q-2D perovskites crystal growth, and ultimately lead to the highest efficiency of 12.81% in (BA)(MA,FA)PbI Q-2D perovskites based photovoltaic devices.

The photovoltaic performance of hybrid halide perovskite solar cells at extreme low temperatures is investigated in depth. Enhanced open-circuit voltage and efficiency are found at temperatures from 290 to 180 K. The mechanism is related to phase-transition-induced self-elimination of intrinsic defects for perovskites at low temperatures. The highest efficiency over 25% at 220 K is ultimately achieved to demonstrate the feasibility of perovskite solar cells in an aerospace environment chamber.

Layered 2D organic–inorganic hybrid perovskite is appearing as a rising star in the photovoltaic field, thanks to its superior moisture resistance by the organic spacer cations. Unfortunately, these cations lead to high exciton binding energy in the 2D perovskites, which suffers from lower efficiency in the devices. It thus requires a clear criterion to select/design appropriate organic spacer cations to improve the device efficiency based on this class of materials. Here, 2,2,2‐trifluoroethylamine (F3EA+) is introduced to combine with butylammonium (BA+) cations as mixed spacers. While BA+ enables self‐assembly of 2D perovskite crystals by van der Waals interaction, the introduction of F3EA+ spacers with a high dipole moment suppress nonradiative recombination and promote separation of photogenerated electron–hole pairs by taking the advantage of electronegativity of fluorine. The resultant solar cells based on [(BA)1–x(F3EA)x]2(MA)3Pb4I13 exhibit substantially increased open circuit voltage and fill factor compared with that of (BA)2(MA)3Pb4I13. The champion [(BA)0.94(F3EA)0.06]2(MA)3Pb4I13 solar cell yields a power conversion efficiency of 12.51%, which is among the best performances so far. These findings suggest an effective strategy to design organic spacer cations in layered perovskite for solar cells and other optoelectronic applications.