High-performance organic photodetectors enabled by a refined fibrillar multiphase morphology

A refined fibrillar multiphase thin-film morphology for organic photodetectors is demonstrated by sequential casting, where from the surface to the bulk, high-quality acceptor crystallites infiltrate the donor fibril network, enabling substantial optimization of device performance. [Display omitted] •An organic photodetector thin-film morphology is demonstrated by sequential casting, where high-quality acceptor crystallites vertically infiltrate the refined donor fibrillar network.•The refined fibrillar multiphase morphology leads to improved charge generation and collection, reduced trap states, and enhanced charge block capability of resultant device.•The sequential-casting devices exhibit a highest special detectivity of 5 × 1013 Jones is achieved at 860 nm under –0.1 V, with improved linear dynamic range and response speed. Film morphology of donor:acceptor blend layers plays a critical role in photon-to-current efficiency and dark/noise current of organic photodetectors (OPDs). One effective approach to manipulate crystallization and mesoscale phase separation of such blend layers is sequential casting (SC). However, the guiding strategies to control the morphology and the impacts on OPD performance of the SC films remain elusive, as the film structural evolution during SC is different from conventional blend casting (BC). Here, a refined fibrillar multiphase morphology is demonstrated by SC in an NT812:IEICO-4F blend film, where the high-quality IEICO-4F crystallites infiltrate the robust NT812 fibril network from the surface to the bulk. Such a morphology leads to improved charge generation and collection, reduced trap states, and enhanced charge block capability of resultant device, enabling simultaneous achievement of high external quantum efficiency and low dark/noise current. A maximum special detectivity of 5 × 1013 Jones is achieved at 860 nm under –0.1 V, which is among the highest detectivities for vis-to-NIR OPDs. The linear dynamic range and response speed are also improved. Such enhancements are parallelly observed from OPD devices based on other blend systems with similar fibrillar refinement, which provides guidelines for film structure manipulation towards high OPD performance.