Novel Noncondensed Acceptors Based on 4H-Dithieno[3,2-B:2′, 3′-D]pyrrole and 4H-Cyclopenta[1,2-B:5,4-B′]Dithiophene N, S-Heterocycles with an Ethynylene Linker for Ternary Polymer Solar Cells with an Efficiency More than 15%

Abstract

This study explores the design, synthesis, and application of two nonfused ring nonfullerene acceptors, namely ECPDT-IC and EDTP-IC, featuring an ethynylene linkers between two 4Hcyclopenta[1,2-b:5,4-b0]dithiophene (CPDT) units and two 4-(2-octyldodecyl)-4H-dithieno[3,2-b:2′, 3′-d]pyrrole (DTP) units, respectively. The incorporation of the ethynylene linker is found to effectively regulate the energy levels and molecular conformations of the nonfullerene acceptors. The EDTP-IC with a DTP central core exhibits higher electron mobility, compared to ECPDT-IC. The frontier energy levels of both ECPDT-IC and EDTP-IC are aligned with PTB7-Th and also showed complementary absorption profiles. The organic solar cells (OSCs) based on PTB7-Th:EDTP-IC attained higher power conversion efficiency (PCE) (13.35%) as compared to the PTB7-Th:ECPDT-IC counterpart (10.87%), attributed to efficient exciton dissociation and charge transport. Further, the PCE has been improved to 15.17% for ternary OSC, when ECPDT-IC was added to PTB7-Th:EDTP-IC binary active layer. The PCE is about 15%, likely due to the active layer's absorption spectrum being limited to 820 nm. However, these NFR-NFAs could be promising for efficient indoor OSCs and as guest components in OSCs with wide bandgap polymers and narrow bandgap acceptors.