Small molecular hole-transporting materials (HTMs) in organic light-emitting diodes (OLEDs): structural diversity and classification

Hole-transporting materials (HTMs) are integral to the construction of a wide variety of state-of-the-art semiconductor devices today. Insofar as display and lighting technologies based on organic light-emitting diodes (OLEDs) are concerned, HTMs are indispensable. Radical development of the area of OLEDs within the last two decades has led to creation of innumerable number of HTMs that are structurally diverse. A better understanding of the structural attributes and structure–property relationships is pivotal for improving the device performance results significantly. We have endeavored to collate, consolidate and discuss the structural milieu, classification, physical properties and electroluminescence data of diverse HTMs. Although our focus of the collection of HTMs is limited to those applied in OLEDs, the inferences drawn from an incisive scrutiny of the chosen structural landscape of HTMs and associated properties are applicable to research on solar cells, field effect transistors, photovoltaics, etc. Consolidated data such as HOMO–LUMOs, Tgs, Tds, hole mobilities, etc. of the HTMs should serve as an invaluable boon to the researchers working in interdisciplinary fields of chemistry, materials science, electrical engineering and physics. Indeed, the review is envisaged to serve as a concise resource of HTMs with important and necessary data.