Alkali metal ions induced high-quality all-inorganic Cs2AgBiBr6 perovskite films for flexible self-powered photodetectors

Lead-free Cs2AgBiBr6 double-perovskite material is a promising all-inorganic candidate substituting organic–inorganic hybrid perovskite for high-efficient optoelectronic devices, especially for daily life application. However, the issue of poor film quality severely restricts the photoelectric performance and flexible application of Cs2AgBiBr6-based devices. In this work, alkali metal ions (Li+, Na+, K+ and Rb+) have been introduced into Cs2AgBiBr6 films. It is proved that the introduction of alkali metal ions plays an important role on film quality and photoresponse performance. High-quality Rb0.1Cs1.9AgBiBr6 films with large grain size, free pin-holes and smooth surface morphology are obtained. The corresponding self-powered Rb0.1Cs1.9AgBiBr6-based photodetectors exhibit 3 orders of magnitude increase of the on–off ratio as well as excellent detectivity of 1.6 × 1013 Jones, large LDR of 177.8 dB and fast response speed of 1.6/1.6 μs. More importantly, benefiting from the improved film quality, flexible Cs2AgBiBr6-based devices with n-i-p and HTL-free heterojunction structure have been fabricated for the first time. Satisfyingly, high on–off ratio of 400, favorable detectivity of 3.2 × 1011 Jones and large LDR up to 152.0 dB are achieved for flexible self-powered Rb+-doped Cs2AgBiBr6 photodetectors. These results suggest a feasible method for Cs2AgBiBr6 film quality improvement and demonstrate a new route to acquire flexible Cs2AgBiBr6 optoelectronic devices.