Direct Optical Patterning of Quantum Dot Light‐Emitting Diodes via In Situ Ligand Exchange

Abstract Precise patterning of quantum dot (QD) layers is an important prerequisite for fabricating QD light‐emitting diode (QLED) displays and other optoelectronic devices. However, conventional patterning methods cannot simultaneously meet the stringent requirements of resolution, throughput, and uniformity of the pattern profile while maintaining a high photoluminescence quantum yield (PLQY) of the patterned QD layers. Here, a specially designed nanocrystal ink is introduced, “photopatternable emissive nanocrystals” (PENs), which satisfies these requirements. Photoacid generators in the PEN inks allow photoresist‐free, high‐resolution optical patterning of QDs through photochemical reactions and in situ ligand exchange in QD films. Various fluorescence and electroluminescence patterns with a feature size down to ≈1.5 µm are demonstrated using red, green, and blue PEN inks. The patterned QD films maintain ≈75% of original PLQY and the electroluminescence characteristics of the patterned QLEDs are comparable to thopse of non‐patterned control devices. The patterning mechanism is elucidated by in‐depth investigation of the photochemical transformations of the photoacid generators and changes in the optical properties of the QDs at each patterning step. This advanced patterning method provides a new way for additive manufacturing of integrated optoelectronic devices using colloidal QDs.