Marina Ustinova

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.

Abstract APbX3 lead perovskites, where A is either an organic (methylammonium MA+ and formamidinium FA+) or an inorganic (Cs+) species, have recently emerged as highly promising photovoltaic materials. This interest is related to the exceptionally high power conversion efficiency (>25%) demonstrated recently in the case of mixed-cation and mixed-halide perovskites. However, the poor intrinsic stability of complex lead halides remains a major hindrance in the commercialization of this emerging photovoltaic technology. An intense research effort is currently focused on revealing the origins and mechanistic aspects of the various pathways of degradation occurring in perovskite solar cells. In this paper, we present a systematic comparative study of a series of mixed-cation perovskite systems: MA0.15FA0.85PbI2.55Br0.45, Cs0.1MA0.15FA0.75PbI2.55Br0.45, Cs0.15FA0.85PbI2.55Br0.45, MA0.15FA0.85PbI3, Cs0.1MA0.15FA0.75PbI3, and Cs0.15FA0.85PbI3 all of which deliver high photovoltaic efficiencies in devices. Using a set of complementary analytical techniques, we demonstrate that bromide-containing mixed-halide perovskites have much lower photostability when compared to the equivalent iodide-based materials. The light-induced photochemical aging produced metallic lead as one of the final decomposition products in the case of all the studied complex lead halides except for Cs0.15FA0.85PbI3, which demonstrated outstanding stability under white light exposure. Theoretical calculations of the bromide-containing mixed-halide perovskites indicated that hole-coupling drives the formation of interstitial-vacancy halide pair defects to become more thermodynamically favorable, thus leading to the accelerated degradation of the halide-mixed perovskites. The obtained results demonstrate the usefulness of compositional engineering as a promising approach to boost the operational stability of perovskite solar cells and pave the way towards their successful commercialization.

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.

The experimental results of X-ray diffraction (XRD), optical absorbance, scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS) of the core levels and valence bands of MAPbBr3 (MA-CH3NH3+) perovskite before and after exposure to visible light for 700 h at temperatures of 10 and 60 °C are presented. It reveals that the light soaking at 60 °C induces the decomposition of MAPbBr3 perovskite accompanied with the decay of organic cation and the release of a PbBr2 phase as a degradation product whereas the photochemical degradation completely disappears while the aging temperature is decreased to 10 °C.

Herein, the synthesis of two novel (X‐DADAD)n conjugated polymers comprising phenylene or fluorene X blocks coupled with benzothiadiazole acceptor (A) and thiophene donor (D) units is reported. The designed polymers are explored as absorber materials in organic solar cells and hole‐transport materials (HTMs) in perovskite solar cells (PSCs). The encouraging efficiencies of ≈17% are obtained in PSCs when using fluorene‐containing polymer P2 featuring this material as a promising HTM for the state‐of‐the‐art 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.

Abstract APbX3 lead perovskites, where A is either an organic (methylammonium MA+ and formamidinium FA+) or an inorganic (Cs+) species, have recently emerged as highly promising photovoltaic materials. This interest is related to the exceptionally high power conversion efficiency (>25%) demonstrated recently in the case of mixed-cation and mixed-halide perovskites. However, the poor intrinsic stability of complex lead halides remains a major hindrance in the commercialization of this emerging photovoltaic technology. An intense research effort is currently focused on revealing the origins and mechanistic aspects of the various pathways of degradation occurring in perovskite solar cells. In this paper, we present a systematic comparative study of a series of mixed-cation perovskite systems: MA0.15FA0.85PbI2.55Br0.45, Cs0.1MA0.15FA0.75PbI2.55Br0.45, Cs0.15FA0.85PbI2.55Br0.45, MA0.15FA0.85PbI3, Cs0.1MA0.15FA0.75PbI3, and Cs0.15FA0.85PbI3 all of which deliver high photovoltaic efficiencies in devices. Using a set of complementary analytical techniques, we demonstrate that bromide-containing mixed-halide perovskites have much lower photostability when compared to the equivalent iodide-based materials. The light-induced photochemical aging produced metallic lead as one of the final decomposition products in the case of all the studied complex lead halides except for Cs0.15FA0.85PbI3, which demonstrated outstanding stability under white light exposure. Theoretical calculations of the bromide-containing mixed-halide perovskites indicated that hole-coupling drives the formation of interstitial-vacancy halide pair defects to become more thermodynamically favorable, thus leading to the accelerated degradation of the halide-mixed perovskites. The obtained results demonstrate the usefulness of compositional engineering as a promising approach to boost the operational stability of perovskite solar cells and pave the way towards their successful commercialization.