Environmentally Friendly Agbis2 Nanocrystal-Based High-Performance Quantum-Dot Photodetectors

Abstract

Pb-free quantum-dot photodetectors (QPDs) are currently being researched upon owing to environmental issues, but relatively low photodetection properties have been reported so far. In this study, we developed high-performance AgBiS2 nanocrystal (NC)-based QPDs with a high responsivity (R) of 0.55 A/W and detectivity (D*) of 1.4×1012 Jones at -0.5 V under 680 nm LED light (1.0 mW/cm2) by incorporating a novel conjugated polyelectrolyte (CPE) as a cathode buffer layer (CBL) on the surface of the electron transporting layer (ETL) in AgBiS2 QPDs. The CPE was developed by co-polymerization between bromohexyl-substituted fluorene and pyrene rings, followed by quaternization with trimethylamine at the terminal alkyl chains. The newly synthesized CPE effectively decreased the work function and reduced the number of trap sites at the ETL surfaces, which increased their photocurrent density and reduced the dark current density, resulting in D* by 3–4.5 times higher than that without the CPE treatment. Notably, our AgBiS2 NC-based QPDs showed an ultrafast rising and falling response time of 1.0 and 3.2 μs, respectively, under the 680 nm LED light, and the CBL layer could rapidly remove residual current density in the off-light state, improving the dynamic characteristics of AgBiS2 QPDs under near-infrared light (940 nm).

Keywords: Pb-free quantum-dot photodetector, AgBiS2 nanocrystal, conjugated polyelectrolyte, cathode buffer layer, near-infrared photodetectors