Synergy between asymmetric contact geometry and self-powered operation of an ultrasensitive CsPbBr3 photodetector

High-performance self-powered photodetectors are in high demand for many applications in wireless sensor networks, Internet-of-things devices, wearable electronics, optical communication, and biomedical sensing. The self-powered photodetector design requires a type-II staggered heterojunction between two semiconductors. Hence, conventional heterojunction-free self-powered photodetector designs remain a challenging task. Here, we report a self-powered photodetector of significantly high performance using an all-inorganic ${\mathrm{Cs}\mathrm{Pb}\mathrm{Br}}_{3}$ monocrystal grown in situ directly over the substrate with prepatterned interdigitated gold ($\mathrm{Au}$) electrodes. Interestingly, we achieved an extremely low dark current of about 1 fA at room temperature, a dark-to-light current ratio of ${10}^{7}$, a responsivity of 2 A/W, and a specific detectivity of ${10}^{14}$ Jones in self-powered mode. The self-powered nature of the $\mathrm{Au}/{\mathrm{Cs}\mathrm{Pb}\mathrm{Br}}_{3}/\mathrm{Au}$ photodetector with asymmetric contact geometry is investigated theoretically using a back-to-back Schottky diode model and experimentally using the Kelvin-probe force microscopy technique. Both approaches converged to predict the existence of a sufficient contact potential difference between the metal contacts due to having an interfacial area difference, which remains the source of built-in potential in the device to dissociate photogenerated excitons effectively for self-powered operation. Our innovative approach in this study opens up an inventive direction for developing a cost-effective heterojunction-free self-powered photodetector.