Quinquethiophene-based fully nonfused electron acceptors towards efficient organic solar cells via side-chain engineering

Abstract

Three fully nonfused electron acceptors based on quinquethiophene (5T) were designed and synthesized via side-chain engineering. Theoretical calculations demonstrate that the introduction of large steric hindrance 2,6-di(hexyloxy)phenyl side chains is beneficial to maintain a coplanar backbone. However, in comparison with two 2,6-di(hexyloxy)phenyl substituted 5T-2P-1 and 5T-2P-2, 2-ethylhexyl substituted 5T-C2C6 film presented more red-shifted absorption, smaller optical bandgap and stronger intermolecular stacking. Nonetheless, when blended with polymer donor D18, 5T-2P-1 with two inner side substituted groups demonstrated a champion power conversion efficiency (PCE) of 12.40%, which outperforms those devices based on D18:5T-C2C6 (5.67%) and D18:5T-2P-2 (10.79%). This was attributed to the excellent miscibility of 5T-2P-1 with D18, more efficient exciton dissociation and charge transport, and higher carrier mobility in D18:5T-2P-1 based devices. This work demonstrates that side-chain engineering of nonfused electron acceptors is an effective strategy for realizing highly efficient OSCs.