High-Gain Self-Powered Photodetector Enabled by Type-II CsPbBr₃ Single Crystal Wafer–CdSeS Quantum Dot Heterojunction for Weak Light Photodetection

To address the demand for high-sensitivity photodetectors under weak light conditions, we have designed a Type-II heterojunction photodetector based on CsPbBr₃ single crystal wafers (SCWs) and CdSeS quantum dots (QDs). High-quality two-dimensional (2D) CsPbBr₃ SCWs were grown using a space confined growth method, while zero-dimensional (0D) CdSeS QDs were prepared by thermal injection. The heterojunctions were constructed by partially coating the CsPbBr₃ SCWs with the CdSeS QDs. Due to the staggered energy band alignment, the built-in electric field was established within the interface, significantly enhancing the separation of photogenerated carriers and effectively suppressing nonradiative recombination. Kelvin probe force microscopy (KPFM) measurements confirmed a surface potential difference of 0.69 V, validating the presence of the built-in field. The device exhibited a low dark current of 1.23 × 10^-11 A and a detectivity (<i>D</i>*) of 1.2 × 10¹³ Jones under weak light illumination. At 5 V bias, the device demonstrated an external quantum efficiency (EQE) of 193%, indicating efficient photocarrier extraction. These results highlight the outstanding performance of the CsPbBr₃-CdSeS Type-II heterojunction for weak light detection and provide a promising approach for high-performance photodetectors.