Synthesis and Photovoltaic Investigation of 8,10-Bis(2-octyldodecyl)-8,10-dihydro-9H-bisthieno[2′,3′:7,8;3″,2″:5,6] naphtho[2,3-d]imidazol-9-one Based Conjugated Polymers Using a Nonfullerene Acceptor

Two donor–acceptor (D–A) conjugated polymers designed on same 8,10-bis(2-octyldodecyl)-8,10-dihydro-9H-bisthieno[2′,3′:7,8;3″,2″:5,6]naphtho[2,3- d]imidazole-9-one donor and dissimilar acceptor units, i.e., benzothiadiazole (P104) and fluorinated benzothiadiazole (P105), were synthesized, and their photophysical and electrochemical properties were investigated. The influence of the incorporation of fluorine atoms into the benzothiadiazole (BT) acceptor moiety in the polymer backbone on the photovoltaic performance when combined with the low bandgap nonfullerene acceptor ITIC-F was explored. The polymer solar cells based on P105:ITIC-F exhibited higher PCE (10.65%) as compared to P104:ITIC-F (8.32%), resulting from the improved values of all the photovoltaic parameters. A high value of Voc is linked with the deeper highest occupied molecular orbital energy level of P105, and the larger values of both short circuit current and fill factor are endorsed to the efficient exciton separation into charge carriers, their subsequent transfer owing to the increased value of dielectric constant and reduced value of exciton dissociation and energy loss, and promoted balanced charge transportation. The intra/interchain interaction can be modulated by F atom substitution in the BT unit, resulting reduction in π–π stacking distance, and increase in the crystal coherence length, benefiting the charge transportation in the active layer. These results offer a simple effective approach to regulate the optical and electrochemical properties and therefore increase the overall photovoltaic response.