A Thieno[3,2-c]Isoquinolin-5(4H)-One Building Block for Efficient Thick-Film Solar Cells

An aromatic lactam acceptor unit, thieno[3,2-c]isoquinolin-5(4H)-one (TIQ), is developed. Compared with its analogues, dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one (DTP) and phenanthridin-6(5H)-one (PN), TIQ shows its advantage in constructing donor–acceptor (D–A) copolymers for efficient solar cells. TIQ-based D–A copolymer PTIQ4TFBT delivers a power conversion efficiency (PCE) of 10.16% in polymer:fullerene solar cells, while those based on DTP and PN copolymers, PDTP4TFBT and PPN4TFBT, afford PCEs around 8.5%. The higher performance of PTIQ4TFBT:PC₇₁BM solar cells originates from enhanced short-circuit current density (J_sc) and fill factor (FF), because of favorable morphology, less bimolecular recombination, and balanced charge transport in the active layer. Moreover, the performance for PTIQ4TFBT:PC₇₁BM solar cells is less sensitive to active layer thickness than PDTP4TFBT:PC₇₁BM and PPN4TFBT:PC₇₁BM solar cells. Over 8% PCEs can be obtained from PTIQ4TFBT:PC₇₁BM solar cells when the active layer thickness is over 500 nm.