High-efficiency oligomeric solar cells - revealing the interplay of molecular dimensions, terminal group functions, and aggregation dynamics

A profound comprehension of the intricate relationships among molecular structure, morphology defining treatment processes, and performance is pivotal for advancing the development of highly efficient organic solar cells (OSCs). In this study, we synthesized a series of donor molecules with varying conjugate skeleton lengths and end-groups, named 3BDTBDD, 5BDTBDD, DRCN3BDT, and DRCN5BDT. Compared to control donors, the oligomer DRCN5BDT exhibits a red-shifted and broader absorption spectrum, enhanced charge-carrier mobility, and optimal crystallinity, attributed to its elongated conjugate skeleton and electron-withdrawing end-group. Consequently, OSCs based on DRCN5BDT:Y6 achieve a remarkable power conversion efficiency (PCE) of 14.04 % in binary oligomer OSCs. Furthermore, DRCN5BDT demonstrated impressive compatibility in ternary OSCs, yielding PCEs of 18.93 % (PM6:DRCN5BDT:BTP-eC9) and 17.45 % (PM6:DRCN5BDT:PY-IT). More importantly, this series of materials provided a clear research framework that enabled us to elucidate the intricate relationship between the widely use yet mystery solvent vapor annealing (SVA) treatment conditions and donor-acceptor aggregation states, employing in situ absorption spectroscopy. Our study provides valuable insights into the intricate connection between molecular structure and properties, offering crucial guidance for the design of efficient donor materials and device optimization of OSCs.