High-Performance Nondoped Blue OLEDs Enabled by HLCT-State Emitters with High Excited Band-Tail Density: An Exciton Energy Distribution Perspective

Excitons in organic semiconductors exhibit an energy distribution due to molecular thermal motion and disordered molecular packing. In our previous work, we modeled the exciton energy distribution using a simple Gaussian function centered at the optical bandgap. By comparing the overlap area (<i>A</i>_ex) between the model and the solution absorption spectra of the emitters, we demonstrated that emitters with a high density of band-tail states are conducive to achieving high device efficiency. Herein, we develop two new blue emitters, TCPN and NCPN, featuring hybridized local and charge transfer (HLCT) and localized excited (LE) states, respectively. We optimize the initial model, including replacing the solution absorption spectra with thin-film excitation spectra, keeping the total number of excitons constant while varying the degree of exciton dispersion, and using the overlap integral (<i>J</i>_ex) instead of <i>A</i>_ex. This work provides novel insights into designing high-efficiency emitters through the lens of the exciton energy distribution.