Dithienobenzothiadiazole-based conjugated polymer: processing solvent-relied interchain aggregation and device performances in field-effect transistors and polymer solar cells

DTfBT-Th(3), a new conjugated polymer based on dithienobenzothiadiazole and terthiophene, possesses a bandgap of ≈1.86 eV and a HOMO level of -5.27 eV. Due to strong interchain aggregation, DTfBT-Th(3) can not be well dissolved in chloro-benzene (CB) and o-dichlorobenzene (DCB) at room temperature (RT), but the polymer can be processed from hot CB and DCB solutions of ≈100 °C. In CB, with a lower solvation ability, a certain polymer chain aggregation can be preserved, even in hot solution. DTfBT-Th(3) displays a field-effect hole mobility of 0.55 cm(2) V(-1) s(-1) when fabricated from hot CB solution, which is higher than that of the device processed from hot DCB (0.16 cm(2) V(-1) s(-1) In DTfBT-Th(3) -based polymer solar cells, a good power conversion efficiency from 5.37% to 6.67% can be achieved with 150-300 nm thick active layers casted from hot CB solution, while the highest efficiency for hot DCB-processed solar cells is only 5.07%. The results demonstrate that using a solvent with a lower solvation ability, as a "wet control" process, is beneficial to preserve strong interchain aggregation of a conjugated polymer during solution processing, showing great potential to improve its performances in optoelectronic devices.