Nanoconfining Optoelectronic Materials for Enhanced Performance and Stability

The solution processing of optoelectronic active layers promises to usher in a new era of technologies, from rollable displays to smart textiles, but critical challenges remain in the processing of these materials. While solution-based deposition of these compounds, including organic small-molecules and polymers and metal–halide perovskites, is key to driving down manufacturing costs, the rapid, uncontrolled nature of solution processing invariably results in the formation of kinetically trapped films, with heterogeneities and defects spanning multiple length scales that degrade device performance. Given such finite time, usually on the order of seconds, for molecules to organize as solvent evaporates from the active layers, the use of nanoporous scaffolds to select for desired crystallization outcomes is a promising approach to addressing this critical issue. As the size of crystals decreases, their surface free energy plays an increasingly important role in dictating their morphology and structure. By confining crystallization within the sub-micrometer pores of scaffolds, such surface free energy effects can be exploited to select for specific polymorphs and crystal orientations. In this Perspective, we highlight the use of nanoporous scaffolds to stabilize high-performing polymorphs of metal-halide perovskites, as well as guide the orientation of organic semiconductor crystals both laterally and vertically for optimized in-plane and out-of-plane charge transport, respectively. Critically, examples of scalable solution-phase deposition methods using nanoporous scaffolds are highlighted as potential targets for commercialization.