Abstract
High ultraviolet(UV)stability and low dark current(Idark)are necessary for high-quality perovskite photodetectors(PDs).TiO2 thin film is known as effective electron-transport-layer(ETL)for perovskite devices.However,common spin-coated TiO2 ETLs endow many surface defects and have strong UV pho-tocatalytic effect to decompose perovskite materials,resulting in inferior stability of devices.In this work,TiO2 bilayer film(Bi-TiO2)has been fabricated by combining spin-coating and atomic-layer-deposition process and its positive effects on UV stability and Idark of Cs2AgBiBr6-based PDs have been revealed for the first time.It is demonstrated that Bi-TiO2 possesses fewer surface defects and smoother morphology with type Ⅱ band alignment,which is beneficial to suppress photocatalytic activity of TiO2 and reduce carrier recombination at the interface.After accelerated strong UV aging treatment,the PD with Bi-TiO2 maintains excellent performance,whereas the PD with spin-coated TiO2 film dramatically deteriorate with on-off ratio drops from～102 to～2.Besides,the Idark of PD remarkably decreases from～10-8 A to～10-10 A after bilayer optimization.Furthermore,we have integrated the corresponding PDs into a self-built imaging system adopting diffuse reflection mode.This work suggests a feasible approach to fabricate TiO2/Cs2AgBiBr6-based PDs with remarkable UV tolerance for imaging applications.
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