Synergistic A-Site Doping in Rb-MAPbBr3/MAPbI3 Crystal Heterojunction for Enhanced Photodetection

Perovskite single crystals offer superior optoelectronic properties but face challenges in spectral response range and device performance. Here, we report a high-performance photodetector based on Rb-doped MAPbBr 3 /MAPbI 3 heterojunction fabricated via liquid-phase epitaxy. Systematic characterization reveals that Rb + incorporation effectively reduces defect density (from 3.02 × 10 9 to 2.48 × 10 9   cm −3 ) and prolongs carrier lifetime (from 12.09   ns to 145.41   ns), while the integration with MAPbI 3 microcrystals extends the spectral response range from the green to the red region (450–750   nm). DFT calculations and UPS reveal that Rb doping tailors the electronic structure of MAPbBr 3 , optimizing band alignment with MAPbI 3 to enhance built-in field for charge separation while increasing work function to suppress dark current. Consequently, the Rb-doped heterojunction device achieves an order-of-magnitude enhancement in both responsivity (600   m   A/W) and detectivity (~2.5 × 10¹² Jones), together with excellent operational and environmental stability (retaining >70% performance after 90 days in air), and a fast response time of 6.29 μs. This work establishes Rb doping as an effective strategy integrating defect passivation and band engineering for high-performance perovskite photodetectors.