Highly efficient, simplified, solution-processed thermally activated delayed-fluorescence organic light-emitting diodes can be realized by using pure-organic thermally activated delayed fluorescence emitters and a multifunctional buffer hole-injection layer, in which high EQE (approximate to 24%) and current efficiency (approximate to 73 cd A(-1)) are demonstrated. High-efficiency fluorescence red-emitting and blue-emitting devices can also be fabricated in this manner.