Poly[[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H- benzo[1,2-c:4,5-c']dithiophene-1,3-diyl][3,3'''-bis(2-ethylhexyl)-3'',4'-difluoro[2,2':5',2'':5'',2'''-quaterthiophene]-5,5'''-diyl]]

PBDD4T-2F polymer semiconductor has been developed for OPV applications (including both fullerene and non-fullerene polymer solar cells) and has an efficiency of over 9% . It has been built into tandem solar cells, and PCE reaching 13% was reported?with the following structure:?PBDD4T-2F:PC71BM (front cell) & PBDTTT-E-T:IEICO (rear cell) [2].