Temperature Dynamics of MAPbI3 and PbI2 Photolysis: Revealing the Interplay between Light and Heat, Two Enemies of Perovskite Photovoltaics.

Regardless of the impressive photovoltaic performances demonstrated for lead halide perovskite solar cells, their practical implementation is severely impeded by the low device stability. Complex lead halides are sensitive to both light and heat, which are unavoidable under realistic solar cell operational conditions. Suppressing these intrinsic degradation pathways requires a thorough understanding of their mechanistic aspects. Herein, we explored the temperature effects in the light-induced decomposition of MAPbI3 and PbI2 thin films under anoxic conditions. The analysis of the aging kinetics revealed that MAPbI3 photolysis and PbI2 photolysis have quite high effective activation energies of ∼85 and ∼106 kJ mol-1, respectively, so decreasing the temperature from 55 to 30 °C can extend the perovskite lifetime by factors of >10-100. These findings suggest that controlling the temperature of the perovskite solar panels might allow the long operational lifetimes (>20 years) required for the practical implementation of this promising technology.

Partial Substitution of Pb2+ in CsPbI3 as an Efficient Strategy To Design Fairly Stable All-Inorganic Perovskite Formulations.

All-inorganic lead halide perovskites, for example, CsPbI3, are becoming more attractive for applications as light absorbers in perovskite solar cells because of higher thermal and photochemical stability as compared to their hybrid analogues. However, a specific drawback of the CsPbI3 absorber consists of the rapid phase transition from black to yellow nonphotoactive phase at low temperatures (e.g., <100 °C), which is accelerated under exposure to light. Herein, an experimental screening of an unprecedently large series (>30) of metal cations in a wide range of concentration has allowed us to establish a set of Pb2+ substitutes, facilitating the crystallization of the photoactive black CsPbI3 phase at low temperatures. Importantly, the appropriate Pb2+ substitution with Ca2+, Sr2+, Ce3+, Nd3+, Gd3+, Tb3+, Dy2+, Er3+, Yb2+, Lu3+, and Pt2+ cations has led to a spectacular enhancement of the film stability under realistic solar cell operation conditions (∼1 sun equivalent light exposure, 50 °C). Optoelectronic, structural, and morphological effects of partial Pb2+ substitution were investigated, providing a deeper insight into the processes underlying the stabilization of the CsPbI3 films. Several CsPb1-xMxI∼3 systems were evaluated as absorber materials in perovskite solar cells, demonstrating encouraging light power conversion efficiency of 11.4% in preliminary experiments. The obtained results feature the potential of designing efficient and stable all-inorganic perovskite solar cells using novel absorber materials rationally designed via compositional engineering.

Incorporation of Vanadium(V) Oxide in Hybrid Hole Transport Layer Enables Long-term Operational Stability of Perovskite Solar Cells.

Recent studies have shown that charge transport interlayers with low gas permeability can increase the operational lifetime of perovskite solar cells serving as a barrier for migration of volatile decomposition products from the photoactive layer. Herein we present a hybrid hole transport layer (HTL) comprised of p-type polytriarylamine (PTAA) polymer and vanadium(V) oxide (VOx). Devices with PTAA/VOx top HTL reach up to 20% efficiency and demonstrate negligible degradation after 4500 h of light soaking, whereas reference cells using PTAA/MoOx as HTL lose ∼50% of their initial efficiency under the same aging conditions. It was shown that the main origin of the enhanced device stability lies in the higher tolerance of VOx toward MAPbI3 compared to the MoOx interlayer, which tends to facilitate perovskite decomposition. Our results demonstrate that the application of PTAA/VOx hybrid HTL enables long-term operational stability of perovskite solar cells, thus bringing them closer to commercial applications.