Colloidal nanocrystals (NCs) have emerged as a diverse class of materials with tunable composition, size, shape, and surface chemistry. From their facile syntheses to their unique optoelectronic properties, these solution-processed nanomaterials are a promising alternative to materials grown as bulk crystals or by vapor-phase methods. However, the use of colloidal nanomaterials in real-world devices is often held back by challenges in depositing them as a patterned two-dimensional layer. This is due to the incompatibility of standard photoresist processes with solution-processed nanomaterials, resulting in non-uniform deposition and/or damage to the deposited NCs. Thus, alternative approaches to patterning colloidal NCs need to be established to aid the transition from individual NC devices to integrated optoelectronic circuits and multi-color NC displays. Here, we discuss the development of stimuli-sensitive ligands that enable colloidal nanomaterials to be patterned directly with good pattern fidelity while retaining desirable properties such as high photo-/electro-luminescence, good carrier mobility and high refractive index. We focus on rationally selected ligands that respond to light, electron-beam and/or heat, allowing the modulation of the NC solubility. This transformation can involve decomposition of ligands, cross-linking of ligands or <i>in situ</i> ligand exchange. We will also explain the suitability of each ligand class for patterning particular types of NCs by evaluating both the ligand molecular chemistry and NC surface binding affinity. Finally, we show the implementation of this direct patterning strategy in the fabrication of NC devices such has field-effect transistors, light-emitting diodes, color-conversion pixels, photodetectors, and diffractive optical elements. Ultimately, this work aims to expediate the implementation of colloidal NCs in a broader range of functional devices.

Stimuli-sensitive ligands for direct lithography of functional inorganic nanomaterials

ACS Spring 2022

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