Surface tailoring enables colloidal quantum dot: Metal-oxide nanocrystal hybrid ink for broadband photon energy conversion

Surface-tailored ZnO nanoparticles were successfully prepared by a modified synthetic route and enables CQD:ZnO hybrid ink. Ink-process without any post-deposition process resulted in favorable heterogeneous morphology and achieved broadband photon energy conversion across visible to near-infrared. [Display omitted] •A new synthetic route successfully tailors the surface properties of ZnO NPs.•Phosphonic acid-terminated NPs successfully enable to control the surface polarity.•The stable mixed heterogenous nanocrystal ink, comprising CQD and ZnO NPs, is demonstrated.•Simple ink-process without any post-deposition process results in favorable heterogeneous morphology and shows broadband photon energy conversion across 350–1100 nm. Blending multiple functional nanoparticles (NPs) into one solvent and forming a stable hetero-ink is a promising technology to realize efficient solution-processed heterogeneous structures for next-generation energy conversion. However, differences in the surface nature of NPs hinder the formation of stable hybrid ink, causing unfavorable morphologies in film formation. In this work, we demonstrate a stable hybrid ink using colloidal quantum dots (CQDs) and metal-oxide NPs. The modified synthesis route of ZnO NPs enables modulation of their surfaces, resulting in ink that is fully miscible in alkyl amine solvents with CQDs. This hybrid ink allows the formation of conformal heterogeneous thin-films via a single step spin-casting. Based on this result, we devise an efficient planar-mixed heterojunction solar cell, which exhibits a 12.8% power conversion efficiency (PCE), one of the highest performances among prior CQD:metal-oxide hetero-structured hybrid solar cells.