All-fluorescent white organic light-emitting diodes employing a deep-blue HLCT material simultaneously as emitter and host achieving excellent electroluminescence performance with efficiency roll-off <1 % at 1000 cd/m2

Simultaneously achieving high efficiency and small efficiency roll-off remains a huge challenge for white organic light-emitting diodes (OLEDs), which greatly restricts their industrial application in the lighting field. Recently developed hybridized local and charge transfer (HLCT) materials have a "hot exciton" channel, which can maximize the utilization rate of excitons and suppress efficiency roll-off via rapid reverse intersystem crossing (RISC) from high-lying triplet state (Tn, n ≥ 2) to singlet state (S1). In this work, employing blue HLCT material pCzAnN as the sensitizing host, by precise concentration management, the traditional fluorescent C545T- and DCJTB-based green and orange-red OLEDs are first fabricated, which achieve the maximum external quantum efficiency (EQE) exceeding the theoretical limit of 5 %, reaching 8.51 % and 6.64 %, respectively. On this basis, by strategic device structure design, all-fluorescent two- and three-color white OLEDs are demonstrated having pCzAnN simultaneously as blue emitter and sensitizing host of C545T and DCJTB. The resulting two- and three-color white devices obtain maximum EQE beyond 5 %. What's more, all three-color white devices exhibit extremely small efficiency roll-off, where the efficiency drops are less than 1 % at a practical luminance of 1000 cd/m2, which is comparable to the best works reported in the literatures. At the same time, the optimized three-color white device realizes ideal white emission, in which the electroluminescence (EL) spectra contain three almost equal intensity emission wavebands accompanied by a high color rendering index of 87. Stable EL spectra under a wide luminance range (3863 ∼ 27710 cd/m2) indicate a huge potential application. We believe this work can provide new idea for developing high-efficiency and low roll-off white OLEDs in the future.