Ultrafast Colloidal Quantum Dot Infrared Photodiode

Lead sulfide (PbS) colloidal quantum dots (QDs) have received attentions as materials for near-infrared (NIR) photodetection in view of their strong and tunable absorption in the NIR region and room-temperature solution processability. However, the realization of high-speed PbS QD photodetection has been severely hindered by the extremely low carrier mobility (∼10–5 to 10–2 cm2 V–1 s–1). Here, an ultrafast PbS QD photodiode fabricated with low mobility QDs (∼10–3 cm2 V–1 s–1) is demonstrated, which has rise/fall times as short as 0.33 μs at zero voltage bias. The fast response is achieved by engineering resistor–capacitor (RC) time delay and charge transport in the device. The photodiode also has an external quantum efficiency (EQE) exceeding 100% under voltage bias, which is possibly due to the photoconductive gain induced by hole transport layer (HTL). The photoconductive gain combined with low noise current enables high sensitivity with a specific detectivity value up to 3.2 × 1011 Jones at 1125 nm.