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The triplet harvesting is a main challenge in organic light-emitting devices(OLEDs), due to the radiative decay of triplet is spin-forbidden. Here, wedesigned and synthesized two D-A type molecules, TPA-TAZ and TCP. The OLEDsbased on them exhibit deep-blue emission and the singlet formation ratios arehigher than the simple spin-statistics of 25 %. Specially, a TPA-TAZ-based OLEDachieves a maximum EQE of 6.8 %, which is the largest value of the undopedOLEDs with CIE(y)< 0.06 (the EBU blue standard) up to date. Comprehensiveexperiments eliminate the triplet-harvesting processes of thermally activateddelayed fluorescence and triplet-triplet annihilation. Instead, thetriplet-polaron interaction induced upconversion from triplet to singletthrough one-electron transfer mechanism is proposed, and proven by themagneto-current measurement and quantum chemistry computation. Our results mayoffer a new route to break through the 25 % upper limit of IQE of fluorescentOLEDs, especially, the deep-blue fluorescent OLEDs.

Triplet-Polaron Interaction Induced Upconversion from Triplet to Singlet: a New Way to Obtain Highly Efficient OLEDs