High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence

Vasilopoulou, Maria and Yusoff, Abd. Rashid bin Mohd and Dabóczi, Mátyás and Conforto, Julio and Gavim, Anderson Emanuel Ximim and Jose da Silva, Wilson and Macedo, Andreia Gerniski and Soultati, Anastasia and Pistolis, George and Schneider, Fabio Kurt and Dong, Yifan and Jacoutot, Polina and Rotas, Georgios and Jang, Jin and Vougioukalakis, Georgios C. and Chochos, Christos L. and Kim, Ji-Seon and Gasparini, Nicola (2021) High efficiency blue organic light-emitting diodes with below-bandgap electroluminescence. NATURE COMMUNICATIONS, 12 (1). ISSN 2041-1723

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Abstract

Blue organic light-emitting diodes require high triplet interlayer materials, which induce large energetic barriers at the interfaces resulting in high device voltages and reduced efficiencies. Here, we alleviate this issue by designing a low triplet energy hole transporting interlayer with high mobility, combined with an interface exciplex that confines excitons at the emissive layer/electron transporting material interface. As a result, blue thermally activated delay fluorescent organic light-emitting diodes with a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency (EQE) of 41.2% were successfully fabricated. These devices also showed suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m−2. Our approach paves the way for further progress through exploring alternative device engineering approaches instead of only focusing on the demanding synthesis of organic compounds with complex structures.

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