A theoretical exploration on why the replacement of hexyl group by alkoxycarbonyl in P3HT could greatly improve the performance of non-fullerene organic solar cell

The PDCBT shows much better performance than P3HT in non-fullerene organic solar cell although the former only replaces hexyl by alkoxycarbonyl group compared with the latter. In this work, we will focus on this tiny difference in structure and huge difference in performance between these two polymers from theoretical perspective. Thus we present a comparative study based on the dependent/time-dependent density functional theory (DFT/TDDFT) calculations and molecular dynamic (MD) simulations. The results reveal that PDCBT not only possesses lower molecular orbital energy levels which leads to the increasement of the open circuit voltage (VOC), but also exhibits better planarity and larger hole mobility than P3HT. In particular, comparing with P3HT system, PDCBT system also displays the higher charge separation rate and smaller charge recombination rate both in hole transfer and electron transfer process at the interface, which promote the enhancement of short-circuit current density. Therefore, this work provides a fundamental understanding of the prominent influence of the replacement of hexyl group by alkoxycarbonyl in P3HT on the cell performance and also provides some theoretical guidance for further optimization of donor materials in non-fullerene organic solar cells (OSCs).