Boosting photodetection performance of Cs₂AgBiBr₆ through A-site Rb substitution and interfacial engineering

Bismuth-based double perovskite Cs₂AgBiBr₆ shows promise as a photodetection material. However, its detection performance and application are limited by high-exciton binding energy and poor carrier mobility. In this study, we address these limitations by delicately designing a solution-based method for incorporating A-site Rubidium (Rb) substitution into Cs₂AgBiBr₆ double perovskite films. The introduction of Rb resulted in a significant decrease in trap defect density and an improvement in film quality. The trap-filled limit voltage (V_TFL) of pure and Rb-doped CABB film is determined to be 1.71 V and 0.48 V, respectively. Subsequently, by introducing an ultrathin atomic-layer-deposited (ALD) TiO₂ films, the fabricated CABB photodetectors exhibit significantly improved photoresponse performance. The response speed and -3dB bandwidth are boosted from ∼93 ms to ∼350 μs and broadened from 1.4 kHz to 17 kHz, respectively. Density Functional Theory (DFT) calculations indicate Rb-substitution shortens the bond length and weaken exciton binding energy. Furthermore, we demonstrate a wireless near ultraviolet (UV) light communication system using CABB photodetectors as light receivers. Our findings provide an efficient approach to utilize A-site cation substitution as a tuning parameter for photodetection in high-exciton binding energy perovskite materials, thereby extending the potential applications of other functional perovskites.