Perovskite solar cells (PSCs) emerging as a promising photovoltaic technology with high efficiency and low manufacturing cost have attracted the attention from all over the world. Both the efficiency and stability of PSCs have increased steadily in recent years, and the research on reducing lead leakage and developing eco-friendly lead-free perovskites pushes forward the commercialization of PSCs step by step. This review summarizes the main progress of PSCs in 2020 and 2021 from the aspects of efficiency, stability, perovskite-based tandem devices, and lead-free PSCs. Moreover, a brief discussion on the development of PSC modules and its challenges toward practical application is provided.

The pathways for the formation of 5-hydroxymethylfurfural (HMF) by dehydration of D-fructose and for the formation of levulinic acid and formic acid from HMF by rehydration were investigated by in situ 13 C and 1 H NMR using both unlabeled and 13 C-labeled fructose. Water or DMSO was used as the solvent with Amberlyst 70, PO 4 3− / niobic acid, or sulfuric acid as catalysts. Only HMF is observed using NMR for fructose dehydration in DMSO with any of the three catalysts or without a catalyst. For each system, results with 13 C-labeled fructose indicate that the first carbon (C-1) or sixth carbon (C-6) of fructose maps onto the corresponding carbons of HMF. For fructose dehydration in H 2 O with a PO 4 3− / niobic acid catalyst, in addition to HMF, furfural was observed as a product. However, we show that furfural is not a reaction product deriving from HMF under our conditions. Rather our data indicate that there is a parallel reaction pathway open to fructose when the reaction takes place in H 2 O with a PO 4 3− /niobic acid catalyst. The corresponding 13 C-labeled results show that the first carbon in fructose maps onto the first carbon (aldehyde carbon) in furfural. Using 13 C-enriched HMF formed from dehydration of 13 C-labeled fructose in DMSO or H 2 O, we investigated the pathway for HMF rehydration to levulinic and formic acid. The data in different solvents and with different catalysts are consistent with a common mechanism for HMF rehydration, which results in the C-1 and C-6 carbon of HMF being transformed to the carbon of formic acid and methyl carbon (C-5) of levulinic acid, respectively.

Perovskite solar cells as a hot research topic show the necessity of controlling the interface. In this work, an insulating alkyl chain layer is self-assembled at the perovskite/hole transport material interface, which successfully exhibits a dual function: blocking electron recombination and resisting moisture at the same time. Improved solar energy conversion efficiency and stability of the device are both achieved.

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The mixtures of cations and anions used in hybrid halide perovskites for high-performance solar cells often undergo element and phase segregation, which limits device lifetime. We adapted Schelling’s model of segregation to study individual cation migration and found that the initial film inhomogeneity accelerates materials degradation. We fabricated perovskite films (FA 1–x Cs x PbI 3 ; where FA is formamidinium) through the addition of selenophene, which led to homogeneous cation distribution that retarded cation aggregation during materials processing and device operation. The resultant devices achieved enhanced efficiency and retained >91% of their initial efficiency after 3190 hours at the maximum power point under 1 sun illumination. We also observe prolonged operational lifetime in devices with initially homogeneous FACsPb(Br 0.13 I 0.87 ) 3 absorbers.