Role of Conjugated Structure of Cross-linkers in Patterned QLEDs

Direct optical lithography is a promising method for the high-resolution patterning of colloidal quantum dots (CQDs) in optoelectronic devices. However, this approach requires photo-cross-linkers that ensure strong chemical binding without degrading CQD ligands, while also supporting efficient charge transport. In this study, we compare two cross-linkers, 4,4′-thiobisbenzenethiol (TBBT) and biphenyl-4,4′-dithiol (BPDT), to evaluate their impact on CQD optoelectronic performance. Density functional theory (DFT) calculations reveal that the biphenyl structure of BPDT enables greater π-orbital overlap and a narrower bandgap than TBBT, which contains sulfur-conjugated units. As a result, BPDT enhances charge injection, preserves photoluminescence, and improves the external quantum efficiency of patterned CQD light-emitting diodes. These findings provide molecular-level insight into cross-linker design strategies for efficient, high-resolution patterning of CQD-based optoelectronics.