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 copolymerpoly(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 a thiophene-conjugated side chain (BDTT) acceptor (A) and donor (D) units respectively and compared its optical and electrochemical properties with well-known polymer PBDB-T, which exhibit same donor unit and different acceptor unit. The P(BDTPtQD)exhibits not only a strong dipole moment but also has a wide bandgap of 1.87 eV as well as a deeper highest occupied molecular (HOMO) energy level of -5.45 eV as compared to PBDB-T. When combined with narrow bandgap nonfullerene acceptor BTP-eC9 and medium bandgap nonfullerene acceptor DBTBT-IC, the optimized binary organic solar cells showed an overall power conversion efficiency 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.