Organic light-emitting devices (OLEDs) are solid-state light-emitting devices based on organic semiconductors. Recent rapid advances in materials chemistry have enabled white OLEDs to be used for general lighting and large-area flat panel display. White OLED panel efficacy has reached 90 lm W–1, and a tandem white OLED panel has achieved a lifetime of over 100000 h at 1000 cd m–2. LG is set to launch a 55″ OLED TV in 2013, and OLEDs will be expected to make bigger breakthroughs. Although white OLED panels show superior performance, there is still much room (nearly 160 lm W–1) for improvement, in view of the theoretical limit of 248 lm W–1. To reach this objective, OLEDs need to achieve three goals: (1) high internal quantum efficiency, (2) low operation voltage, and (3) high light-outcoupling efficiency at the same time. For organic chemists creating new organic semiconductors, issues (1) and (2) are particularly important because these relate to materials chemistry. Here we review recent developments in phosphorescent OLED technology, especially from materials chemistry.