Low‐Bandgap Methylammonium‐Rubidium Cation Sn‐Rich Perovskites for Efficient Ultraviolet–Visible–Near Infrared Photodetectors

Solution-processed and low-temperature Sn-rich perovskites show their low bandgap of about 1.2 eV, enabling potential applications in next-generation cost-effective ultraviolet (UV)-visible (vis)-near infrared (NIR) photodetection. Particularly, the crystallization (crystallinity and orientation) and film (smooth and dense film) properties of Sn-rich perovskites are critical for efficient photodetectors, but are limitedly studied. Here, controllable crystallization for growing high-quality films with the improvements of increased crystallinity and strengthened preferred orientation through a introducing rubidium cation into the methylammonium Sn-Pb perovskite system (65% Sn) is achieved. Fundamentally, the theoretical results show that rubidium incorporation causes lower surface energy of (110) plane, facilitating growth in the dominating plane and suppressing growth of other competing planes. Consequently, the methylammonium-rubidium Sn-Pb perovskite photodetectors simultaneously achieve larger photocurrent and lower noise current. Finally, highly efficient UV-vis-NIR (300-1100 nm) photodetectors with record-high linear dynamic range of 110 and 3 dB cut-off frequency reaching 1 MHz are demonstrated. This work contributes to enriching the cation selection in Sn-Pb perovskite systems and offering a promising candidate for low-cost UV-vis-NIR photodetection.