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Overcoming the energy gap law in near-infrared OLEDs by exciton-vibration decoupling

Yu-Chen Wei, Sheng Fu Wang, Yun Hu, Liang-Sheng Liaomail, Deng-Gao Chen, Kai-Hsin Chang, Chi-Wei Wang, Shih-Hung Liu, Wei-Hsiang Chan, Jia-Ling Liao, Wen-Yi Hung, Tsai-Hui Wang, Po-Ting Chen, Hsiu-Fu Hsu, Yun Chimail, Pi-Tai Choumail.

 

Nature Photonics, 14, pages570–577 (2020)

https://www.nature.com/articles/s41566-020-0653-6

 

Abstract

The development of high-performance near-infrared organic light-emitting diodes is hindered by strong non-radiative processes as governed by the energy gap law. Here, we show that exciton delocalization, which serves to decouple the exciton band from highly vibrational ladders in the S0 ground state, can bring substantial enhancements in the photoluminescence quantum yield of emitters, bypassing the energy gap law. Experimental proof is provided by the design and synthesis of a series of new Pt(II) complexes with a delocalization length of 5–9 molecules that emit at 866–960 nm with a photoluminescence quantum yield of 5–12% in solid films. The corresponding near-infrared organic light-emitting diodes emit light with a 930 nm peak wavelength and a high external quantum efficiency up to 2.14% and a radiance of 41.6 W sr−1 m−2. Both theoretical and experimental results confirm the exciton–vibration decoupling strategy, which should be broadly applicable to other well-aligned molecular solids.