The Least-Ordered of Three Deep-Blue Phosphine-Oxide Hosts Still Conducts Holes Cleanly

Deep-blue phosphine-oxide hosts are compared by energy levels and photophysics, almost never by microstructure—yet order and film morphology are routinely read as proxies for how well a host will carry charge. Here three related hosts are compared from primary particles to film relief with documented, protocol-tested descriptors. The tert-butyl-substituted S3 host emerges as the least ordered on every scale: the lowest X-ray ordered fraction at every baseline setting, the shortest film correlation, micrometre-scale relief and the lowest decomposition temperature, while only the S1 host shows lattice fringes. Disorder, however, does not spoil its hole transport. The S3 hole-only device shows a single, nearly ideal relaxation with a capacitance close to the geometric value and an apparent hole mobility of about 5 × 10−7 cm2 V−1 s−1, comparable to that of the far better-ordered S1 host. Long-range disorder in these hosts is therefore compatible with clean hole transport, and microstructure alone is not a reliable screen for transport.