Phase‐Modulated Multidimensional Perovskites for High‐Sensitivity Self‐Powered UV Photodetectors

2D Ruddlesden‐Popper perovskites (PVKs) have recently shown overwhelming potential in various optoelectronic devices on account of enhanced stability to their 3D counterparts. So far, regulating the phase distribution and orientation of 2D perovskite thin films remains challenging to achieve efficient charge transport. This work elucidates the balance struck between sufficient gradient sedimentation of perovskite colloids and less formation of small‐n phases, which results in the layered alignment of phase compositions and thus in enhanced photoresponse. The solvent engineering strategy, together with the introduction of poly(3,4‐ethylene‐dioxythiophene):polystyrene sulfonate (PEDOT:PSS) and PC71BM layer jointly contribute to outstanding self‐powered performance of indium tin oxide/PEDOT:PSS/PVK/PC71BM/Ag device, with a photocurrent of 18.4 µA and an on/off ratio up to 2800. The as‐fabricated photodetector exhibits high sensitivity characteristics with the peak responsivity of 0.22 A W−1 and the detectivity up to 1.3 × 1012 Jones detected at UV‐A region, outperforming most reported perovskite‐based UV photodetectors and maintaining high stability over a wide spectrum ranging from UV to visible region. This discovery supplies deep insights into the control of ordered phases and crystallinity in quasi‐2D perovskite films for high‐performance optoelectronic devices. Quasi‐2D Ruddlesden‐Popper perovskite thin films PEA2MA3Pb4I13 with uniform crystalline morphology and gradient phase distribution are successfully prepared via dimethylsulfoxide content modulation, which gives rise to the enhancement of photoresponse under zero bias voltage. The solvent engineering strategy, together with the introduction of poly(3,4‐ethylene‐dioxythiophene):polystyrene sulfonate (PEDOT:PSS) and PC71BM layer jointly contribute to outstanding optoelectronic performance of ITO/PEDOT:PSS/perovskites/PC71BM/Ag device with high sensitivity.