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 10 9 to 10 11 cm Hz 1/2 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.

Fast Near‐Infrared Photodetectors Based on Nontoxic and Solution‐Processable AgBiS2

“…In Equation 3, V is the applied voltage across the two electrodes of the photodiode, d the thickness of the photoactive layer, and μ e and μ h the electron and hole mobilities, respectively. In most solution-processed NIR PDs, d is at least a few hundreds of nanometers in order to achieve sufficient light absorption, [7,15,36] and their f −3dB values would thus be limited by the long transit distances required. In addition, organic PDs suffer from low or unbalanced charge-carrier [29,44] which could further lower their f −3dB values, since charge-carrier transport will be limited by the smallest charge-carrier mobility.…”

“…However, silicon-based PDs are usually bulky and require sophisticated manufacturing processes, making them less attractive as portable or wearable devices. On the other hand, organic materials, [10][11][12] lead-halide perovskites, [7,13] and chalcogenide quantum dots (QDs) [14][15][16] have demonstrated higher absorption coefficients in the NIR region than silicon, and their solution processability at low temperatures enables them to be compatible with polymer substrates, which are ideal for flexible and lightweight electronics. Nevertheless, NIR PDs based on these materials also face various challenges.…”

Lead Chalcogenide Colloidal Quantum Dots for Infrared Photodetectors

“…The addition of CH3NH3PbI3 enabled PbS CQDs to generate greater gains. To further reduce the dark current of the device, in 2020, Ka et al reported a strategy combining copper thiocyanate (CuSCN) and PbS CQDs to reduce the dark current of PbS CQD-based photodetectors [73] (Figure 8h,i). The detectivity of the prepared photodiode could reach 10 11 Jones.…”