Nobuhiko Akino1
Hosei University1
Recently, organic light emitting diodes (OLEDs) have been utilized in smartphones, large-size displays and solid-state lightings due to their desirable characteristics such as self-emission, high-speed response, light weight and so on. For the light emitting materials in OLEDs, the emission spectrum profile is one of the most important material properties as it determines not only the emission color, but also the device efficiency. Especially for the display applications, the material with sharp spectral profile is essential to achieve a better color gamut and also to avoid any loss by the energy filter. Hence, it has been highly desired to simulate the spectrum profile, that is, not only the peak wavelength of absorption and/or emission, but also its overall spectrum shape.<br/> In order to study the spectrum profile of materials, the time dependent density functional theory (TDDFT) has been employed [1]. This is one of the most prominent and widely used methods for calculating excited states of medium-to-large molecules, and it is recognized as a powerful tool for studying electronic transition of molecules. The TDDFT code used in this study is based on the real-space and real-time (RSRT) formalism [2]. One of the advantages of this real-space and real-time formalism is that one can keep the code simple and understand physical meanings as directly as possible. Since this formalism is suitable for large-scale parallel computing, its MPI parallelized code has been developed and be applied to large molecules depending on the computer resources. Furthermore, the use of maximum entropy method has also been studied to extract spectrum peak information with limited real-time data [3].<br/>This RSRT approach has been applied to some typical organic materials such as poly-(9,9'-dialkyl-fluorene) as a fluorescent material, tri(2-phenylpyridinato)iridium(III), Ir(ppy)<sub>3</sub>, as a phosphorescent material, and 4CzIPN and DABNA-1 as a thermally activated delayed fluorescent (TADF) materials. The results have been suggesting that although some redshift of the peak wavelength is observed, the simulated spectral profiles agree very well with the experimentally observed profiles [4,5].<br/>In the presentation, with utilizing both the RSRT-TDDFT and commercial quantum chemical software, TADF molecules will be studied in order to obtain design rules and possibly new molecules with desired spectrum profile in RGB region.<br/> <br/>REFERENCES<br/>[1] E. Runge and E. K. U. Gross, Phys. Rev. Lett. <b>52</b>, 997 (1984)<br/>[2] K. Yabana and G. F. Bertisch, <i>Phys. Rev. </i>B<b>54</b>, 4484 (1996)<br/>[3] M. Toogoshi, S. S. Kano, Y. Zempo, J. Phys.: Conf. Series. 510, 012027 (2014)<br/>[4] N. Akino and Y. Zempo, J. Phys.: Conf. Ser. <b>2207</b> 012039 (2022)<br/>[5] N. Akino, MRS Advances <b>7</b>, 310(2022)