Broadband Self-Powered CdS ETL-Based MAPbI Heterojunction Photodetector Induced by a Photovoltaic-Pyroelectric-Thermoelectric Effect.

CdS, with a noncentrosymmetric structure, is thought as an important electron transport layer (ETL) in perovskite-based devices, but its pyroelectric effect, which can efficiently modulate the optoelectronic processes, is not well explored. In this work, a MAPbI heterojunction of CdS/MAPbI/Spiro-OMeTAD with a -axis preferred oxygen-doped CdS ETL is developed as a high-performance photodetector (PD). This PD exhibits a stable self-powered property in the spectral range of ∼360-780 nm due to its excellent photovoltaic effect. Moreover, the light-induced pyroelectric potential in the CdS ETL is demonstrated to be an efficient approach for improving the photoresponses, and different effects are observed for different laser irradiations, which can be well understood from their working mechanisms. Upon 450 nm laser irradiation, the photovoltage responsivity () is greatly improved from 596.9 to 6383.6 V/W with an increment of 1069.54%. In addition, the response spectrum is also extended outside the bandgap restriction of the MAPbI to 1550 nm due to both the pyroelectric and photothermoelectric effects, which is a big breakthrough for the perovskite heterojunction PD. Through turning the external bias voltage and ambient temperature, the coupling mechanisms of the pyroelectric and photovoltaic effects are further analyzed. This work provides an important understanding of designing the CdS ETL-based perovskite heterojunction for broadband high-performance photoelectric devices by introducing the pyroelectric effect.