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Quasi‐two‐dimensional (Q‐2D) perovskites are emerging as one of the most promising materials for photodetectors. However, a significant challenge to Q‐2D perovskites for photodetection is their insufficient charge transport ability, which is mainly attributed to their hybrid low‐dimensional n‐phase structure. This study demonstrates that evenly‐distributed 3D‐like phases with vertical orientation throughout the film can greatly facilitate charge transport and suppress charge recombination, outperforming the prevalent phase structure with a vertical dimension gradient. Based on such a phase structure, a Q‐2D Ruddlesden−Popper perovskite self‐powered photodetector achieving a combination of exceptional figures‐of‐merit is realized, including a responsivity of 0.45 AW−1, a peak specific detectivity of 2.3 × 1013 Jones, a 156 dB linear dynamic range, and a rise/fall time of 2.89 µs/1.93 µs. The desired phase structure is obtained by utilizing a double‐hole transport layer (HTL), combining hydrophobic PTAA and hydrophilic PEDOT: PSS. Besides, the dependence of the hybrid low‐dimensional phase structure is also identified on the surface energy of the buried HTL substrate. This study gives insight into the correlation between Q‐2D perovskites' phase structure and performance, providing a valuable design guide for Q‐2D perovskite‐based photodetectors. [ABSTRACT FROM AUTHOR]

Selective electron transport and extraction are essential to the operation of photovoltaic devices. Electron transport layer (ETL) is therefore critical to organic photovoltaics (OPV). Herein, an ETL configuration is presented comprising a solution‐processed n‐n organic heterojunction to enhance electron transport and hole blocking, and boost power conversion efficiency (PCE) in OPV. Specifically, the n‐n heterojunction is constructed by stacking a narrow‐band n‐type conjugated polymer layer (PNDIT‐F3N) and a wide‐band n‐type conjugated molecule layer (Phen‐NaDPO). Based on the ultraviolet photoelectron spectroscopy measurement and numerical simulation of current density‐voltage characteristics, the formation of the built‐in potential is investigated. In three OPVs with different active layers, substantial improvements are observed in performance following the introduction of this ETL configuration. The performance enhancement arises from the combination of selective carrier transport properties and reduced recombination. Another contributing factor is the good film‐forming quality of the new ETL configuration, where the surface energies of the related materials are well‐matched. The n‐n organic heterojunction represents a viable and promising ETL construction strategy for efficient OPV devices. [ABSTRACT FROM AUTHOR]