Cation-Exchanged quantum Dot-Based high-performance near-infrared photodetectors through surface treatment and passivation

Cation-exchange (CE) is a straightforward method for synthesizing colloidal quantum dots (CQDs) comprising multiple elements. However, the responsivity of photoconductors using cation-exchanged CQDs remains limited due to surface traps induced by the CE process. In this study a flexible near-infrared (NIR) photoconductive detector that exhibits the high responsivity (457 mA/W) under NIR light compared to reported Ag₂Se CQD photodetector is fabricated using partially cation exchanged Cd_xAg_2-xSe CQDs. The as-synthesized CdSe CQDs were transformed into Cd_xAg_2-xSe CQDs through the introduction of an Ag precursor to enhance their NIR absorption characteristics and preserve their cubic structures. To mitigate surface traps associated with cation-exchanged CQDs, solution-phase ligand-exchange and post-treatment for surface passivation are incorporated using InBr₃. In and Br ions are utilized to fill the surface vacancies of the CQDs and passivate the dangling bonds, reducing nonradiative recombination sites. Structural and optical analyses confirm the passivation of trap states. In addition, indium passivation improves the Seebeck coefficient and mobility, resulting in enhanced responsivity. This study underscores the importance of surface passivation in the CE method, thereby contributing to the future CQDs development with multiple elements.