Theoretical study of the charge separation process in NTz-based fluorinated non-fullerene type organic thin-film solar cells

In order to further improve the light conversion efficiency of organic thin-film solar cells (OSCs), it is important to search for high-performance donor (D)/acceptor (A) materials based on the elucidation of exciton dynamics and photoelectric conversion mechanism at the D/A laminated structure interface. Recently, it has been reported that the bulk heterojunction OSCs, which contain fluorinated naphtho [1,2-c:5,6-c'] bis [1,2,5] thiadiazole-based non-fullerene acceptors has a better photovoltaic performance [1]. In this study, we calculated absorption spectra, excitation energy transfer (EET), the amount of transferred charge and the charge transferred distance with the non-fullerene complex PCPD-TBT (D)/NTz-T_eh–FA (A) and the fluorinated PCPD-TBT (D)/FNTz-T_eh-FA (A). We performed DFT calculations with ωB97XD/6-31G(d) using Gaussian16. Comparing fluorination with non-fluorination, since the charge transfer distance is long, it is considered that there is a strong tendency for a 'hot process' that does not involve the charge transfer state between the exciton generation and the charge separation state. In addition, it is considered that the charge separation efficiency is increased from EET.

[1] S. Chatterjee, Y. Ie, et. al., NPG Asia Mater., 10, 1016-1028 (2018)