High-efficiency, long-lifetime deep-blue organic light-emitting diodes

Simultaneously achieving both a high efficiency and long lifetime in deep-blue organic light-emitting diodes is challenging. Here we report thermally activated delayed fluorescence (TADF) organic light-emitting diodes that aim to meet this goal by combining a new design of blue TADF materials with a triplet-exciton recycling protocol. Two TADF materials, one distributing and one emitting, were doped into a host to form triplet-exciton-distributed TADF devices. The singlet excitons were transferred from the host to the emitter via the distributing TADF material by cascade energy transfer, whereas the triplet excitons were transferred to the emitter as singlet excitons by a triplet-exciton recycling process between the low-triplet-energy host and the distributing TADF material. The resulting triplet-exciton-distributed TADF devices achieved a high external quantum efficiency of 33.5 ± 0.1, a colour coordinate corrected current efficiency over 400 cd A^–1, a lifetime of >5,000 h and a y colour coordinate below 0.10.