Solution-Processed p-Type Copper Thiocyanate (CuSCN) Enhanced Sensitivity of PbS-Quantum-Dots-Based Photodiode

Abstract

Lead sulfide (PbS) quantum dots (QDs) exhibit outstanding size-dependent properties that can be harnessed for optoelectronic applications. For example, they can be used for broadband light detection thanks to their band gap, which can be tuned from the UV to near-infrared. Recent reports show that reducing the dark current in PbS-QDs-based photodetectors leads to improved performance. To this end, we explore the use of low-cost solution-processed p-type copper thiocyanate (CuSCN) films as hole-transporting layer in PbS-QD-based photodetectors. We demonstrate that depositing the CuSCN layer prior to the evaporation of the metal electrode (silver or gold) significantly reduces the dark current, regardless of the electrode material. In turn, the on–off ratio and the detectivity of the fabricated photodiodes have also been improved from 6 to 200 and 109 to 1011 cm Hz1/2 W–1, respectively. Moreover, the response time of the photodiodes is preserved when using the CuSCN layer. The thin CuSCN film incorporated between the PbS QD layer and the metal electrode can be engineered to enhance the performance of broadband photodetectors, in a way that is compatible with standard processing approaches.