Hybrid-Size Quantum Dots in Hole Transport Layer Depress Dark Current Density of Short-Wave Infrared Photodetectors

PbS quantum dots (QDs) are promising materials for low-cost short-wave infrared (SWIR) photodetection and imaging applications, owing to their unique optical properties and tunable bandgap. High-performance photodiodes rely on thiol-treated small PbS QDs as the hole transport layer (HTL) due to their suitable band alignment, but they face challenges such as crack formation, which increases dark currents. We develop a crack-free HTL by mixing small-size and large-size QDs. Grazing incidence small-angle X-ray scattering data confirms that the hybrid-size QD HTL is more homogeneous and denser than that made from monosize QDs. Photophysical studies show optimized charge carrier dynamics and energy transfer in the hybrid-size QDs, compared to monosize QDs. The devices based on the hybrid-size QD HTL exhibit a significantly reduced dark current density (392 nA/cm²). Additionally, they show high device performance, including a responsivity of 0.65 A/W, detectivity of 2.4 × 10¹² Jones, and an external quantum efficiency of 65% in the SWIR region, paving the way for high-performance QD-based SWIR photodetectors.