Improving the electron transport performance by changing side chains in sulfur-containing azaacenes: a combined theoretical investigation on free molecules and an adsorption system

Density functional theory and semi-classical Marcus electron transfer theory were employed to investigate the electron transport properties of a sulfur-containing azaacene molecule 10,14-bis(5-(2-ethylhexyl)thiophen-2-yl)dipyrido[3,2-a:20,30-c][1,2,5]thiadiazolo[3,4-i]phenazine (TDTP), which has been proved to have high performance as an electron transport material in inverted perovskite solar cells in a previous experiment. By changing thiophene rings in both side chains to thiazole/benzene rings, two new compounds TDTP-I and TDTP-II were designed. It has been found that both new compounds have lower HOMO and LUMO energy levels and higher electron mobilities than TDTP. In particular, compound TDTP-II has the highest electron mobility among the three. Furthermore, the adsorption properties of TDTP/TDTP-II adsorbed on perovskite (110) surface systems are also studied. It has been shown that TDTP-II has a more negative adsorption energy than TDTP. So our designed compound TDTP-II is expected to be a potential electron transport material in inverted PSCs and changing the side chains could be a feasible way to improve the electron transport properties.