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Wide‐bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open‐circuit voltage (VOC) deficit and serious photo‐induced halide segregation remain the main challenges that impede their applications. Herein, a post‐treatment strategy without thermal annealing is presented to form a 2D top layer of 2‐thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing‐free post‐treatment method can more effectively passivate the defects of WBG methylamine (MA)‐free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo‐induced perovskite phase segregation, as compared with the thermal annealing method that yields multi‐2D phases. The resulting opaque and semi‐transparent 1.66 eV‐bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small VOC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA‐free WBG PSCs. Consequently, four‐terminal all‐perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi‐junction tandem solar cells. [ABSTRACT FROM AUTHOR]

Electron transport materials (ETMs) play an important role in organic solar cells (OSCs) and the rapidly evolving non-fullerene acceptors have higher demands for ETMs. A novel naphthalene diimide-based conjugated polymer (PNDI-NN) with aliphatic amino side chains at the N-position of naphthalene diimide was synthesized and introduced as an ETM in non-fullerene OSCs. The only N-substituted aliphatic amino side chains endow PNDI-NN with good solubility in alcohol and an intense self-doping effect, which can not only reduce the work function of the metal electrode (Ag), but also have a good coverage on the active layer and promote electron transport. The device with PNDI-NN showed the best power conversion efficiency of 15.6% with an improved open-circuit voltage (VOC) and fill factor (FF). The device also exhibited good long-term stability in an inert atmosphere, in a humid environment and under continuous heating. [ABSTRACT FROM AUTHOR]

The hole-transport material (HTM) free carbon-based perovskite solar cells (C–PSCs) lacks a HTM layer inside, resulting in poor charge transport performance. The power conversion efficiencies (PCE) of the C–PSCs could be effectively improved by increasing the transmission of photo-generated electrons from the perovskite to the electron transport layer. Here, the nanoparticles with TiO 2 @ PbTiO 3 core-shell structure were prepared by in-situ reaction and used as mesoporous electron transport layer to improve electron transport performance. It is worth noting that the density of defect states on the surface of TiO 2 significantly reduced due to the coating of PbTiO 3 , which effectively inhibits the interfacial charge recombination caused by the defect as the carrier recombination center. The electron injection from perovskite to electron transport layer enhanced ascribing to the optimized energy band arrangement. The open circuit voltage (V oc) and short circuit density (J sc) were significantly improved, as well as the hysteresis retarded. Finally, the optimal PCE prepared in the air condition increased from 6.55% to 7.97%. This study provides a very feasible idea for obtaining high-performance C–PSCs. Image 1 • The TiO 2 @PbTiO 3 core-shell structure using for mesoporous layer was fabricated by the in-situ reaction. • The trap states density acted as the center of charge recombination reduced significantly ascribing to the PbTiO 3 shell. • The electron injection from perovskite to electron transport layer enhanced due to the optimized energy band arrangement. • The open circuit voltage and short circuit density of cells improved apparently, and retarded the hysteresis. [ABSTRACT FROM AUTHOR]