Planar Cation Passivation on Colloidal Quantum Dots Enables High-Performance 0.35–1.8 µm 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 (E_g ≈ 0.74 eV) is reduced from 2.74 × 10¹⁵ to 1.04  × 10¹⁵ cm⁻³, coupled with 0.1 eV 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 98 dB, a −3dB bandwidth of 103 kHz and a detectivity of 4.7 × 10¹¹ Jones. The comprehensive performance of the CQDs photodiodes outperforms previously reported CQDs photodiodes operating at >1.6 µm. By monolithically integrated with thin-film transistor (TFT) readout circuit, the broadband CQDs imager covering 0.35-1.8 µm realizes the functions including silicon wafer perspectivity and material discrimination, showing its potential for wide range of applications.