Surface Photochemistry Enabled Direct Patterning of Colloidal Inorganic Nanocrystals: From 2D to 3D.

Colloidal inorganic nanocrystals (NCs), especially semiconductor quantum dots (QDs), serve as versatile building blocks for solution-processable electronics, optoelectronics, and photonics. As the field moves toward integrated, system-level applications, such as QD light emitting diode (QLED) displays, precise patterning of colloidal NCs in two- (2D) and three-dimensions (3D) while preserving their material functionalities becomes increasingly critical. Direct photopatterning strategies, based on the photochemical transformation of NC surface ligands to modulate colloidal stability, have recently emerged as powerful approaches, offering excellent resolution, fidelity, and material compatibility. In this review, we highlight recent progress in direct photopatterning of colloidal NCs, with particular focus on the rational design of photochemistry, its influence on the properties of patterned NCs and devices, and its applications in 3D nanoprinting. We outline four representative photochemical transformation strategies that underpin direct 2D photopatterning approaches. We then examine how these strategies affect the key properties of patterned NC layers and the performance of pixelated QLEDs. We further summarize emerging advancements in the direct 3D nanoprinting of NCs, emphasizing the role of interparticle bonding chemistry and comparing the distinctions between 2D and 3D approaches. We conclude with an outlook on challenges and future directions.