Photoabsorption of acceptor molecules in non-fullerene type organic thin film solar cells

The π-conjugated system is important as a semiconductor material in organic electronics such as organic light emitting diodes, field effect transistors, and organic solar cells (OSCs). Organic semiconductors can adjust the energy levels of HOMO and LUMO, so it is also possible to adjust the relative energy between the molecular orbital of the organic semiconductor and the Fermi level of the metal electrode. Therefore, selective insertion/transport of holes/electrons is essential to the realization of organic devices. 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. In this study, we theoretically investigate the effects of fluorine atoms on the properties and photovoltaic performance from the perspective of molecular structure, HOMO-LUMO energy gap, and absorption spectrum. FNTz-T_eh-FA was found to have a lower LUMO energy. Therefore, by fluorine substitution, it is expected that J_SC will be increased, and charge separation will be enhanced. These results provide the key to develop new organic semiconductors with the application of donor-acceptor type donors and non-fullerene acceptor materials in OSCs.