Planar Cation Passivation on Colloidal Quantum Dots Enables High-Performance 0.35-1.8µm Broadband TFT Imager.

Abstract

Solution-processed colloidal quantum dots (CQDs) are promising candidates for broadband photodetectors from visible light to shortwave infrared (SWIR). However, large-size PbS CQDs sensitive to longer SWIR are mainly exposed with nonpolar (100) facets on the surface, which lack robust passivation strategies. Herein, an innovative passivation strategy that employs planar cation, is introduced to enable face-to-face coupling on (100) facets and strengthen halide passivation on (111) facets. The defect density of CQDs film (Eg ≈ 0.74eV) is reduced from 2.74×1015 to 1.04×1015 cm-3 , coupled with 0.1eV reduction in the activation energy of defects. The resultant CQDs photodiodes exhibit a low dark current density of 14 nA cm-2 with a high external quantum efficiency (EQE) of 62%, achieving a linear dynamic range of 98dB, a -3dB bandwidth of 103kHz and a detectivity of 4.7×1011 Jones. The comprehensive performance of the CQDs photodiodes outperforms previously reported CQDs photodiodes operating at >1.6µm. By monolithically integrated with thin-film transistor (TFT) readout circuit, the broadband CQDs imager covering 0.35-1.8µm realizes the functions including silicon wafer perspectivity and material discrimination, showing its potential for wide range of applications.