Effect of chemical modifications on PCDTBT were studied by DFT and TD-DFT.
Large deviations in Φ and Δr in chemically modified PCDTBT greatly increases EGap and EOpt.
The EGap and EOpt of PCDTBT may be lowered by both electron-withdrawing and electron-donating substituents.
Coplanar thiophene and substituted benzothiadiazole units in PCDTBT derivatives may lead to increased light absorption.
PCDTBT-F may have superior solar cell properties: ISC, VOC, and IP, than PCDTBT.