A novel pyrrolo[3,4-b]dithieno[2,3-f:3′,2′-h]quinoxaline-8,10(9H)-dione-based medium bandgap π-conjugated polymer donor for high-performance ternary non-fullerene polymer solar cells with an efficiency of over 17%

Abstract

A D–A copolymer, poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl)-co-(9-(2-octyldodecyl)-8H-pyrrolo[3,4-b]dithieno[2,3-f:3′,2′-h]quinoxaline-8,10(9H)-dione), denoted as P(BDTPtQD)—consisting of dithienoquinoxalineimide (DTQxI) as the acceptor (A) and benzodithiophene with thiophene-conjugated side chain (BDTT) as the donor (D) unit—was synthesized and its optical and electrochemical properties were compared with those of the well-known polymer PBDB-T, which exhibits the same donor unit and a different acceptor unit. P(BDTPtQD) exhibits a large dipole moment, a wide bandgap of 1.87 eV, and a deeper highest occupied molecular orbital (HOMO) energy level of −5.45 eV as compared to PBDB-T. When combined with narrow bandgap non-fullerene acceptor BTP-eC9 and medium bandgap non-fullerene acceptor DBTBT-IC, the optimized binary organic solar cells showed an overall power conversion efficiencies of 14.84 and 12.81%, respectively. Following the addition of DBTBT-IC to the P(BDTPtQD) : BTP-eC9 binary host, ternary organic solar cells fabricated under air-processed conditions achieved a power conversion efficiency of 17.26%. The improvement in the power conversion efficiency of the ternary organic solar cell is attributed to the denser π–π stacking distance, the longer crystal coherence length of π–π stacking, efficient exciton utilization through energy transfer from DBTBT-IC to BTP-eC9, lower trap density, and minimized recombination losses.