Beyond single numbers: how to choose host materials for deep-blue TADF OLEDs

Deep-blue thermally activated delayed fluorescence (TADF) OLEDs stand or fall on their host, yet hosts are still chosen from a handful of single numbers: triplet energy, singlet–triplet gap, frontier levels, glass transition and carrier mobility. We compiled these descriptors for sixteen hosts and cohost components from six chemical families, tracing the source, method and condition behind every value, and find that most are protocol-dependent observables rather than material constants: published triplet energies of one molecule differ by up to 0.12 eV, and five analyses of the same devices place one host’s electron-to-hole mobility ratio anywhere between 0.77 and 3.1. A one-protocol calculation of 50 molecules shows that computed-gap rankings depend on functional choice and require validation against measurement. We review how exciplex-forming, mixed and sensitised hosts share the host’s tasks and what limits operational stability, and propose a minimum reporting standard and a roadmap toward protocol-locked, multi-descriptor host selection.