Importance of halogenated side-chain in small molecule acceptors on optimizing blend morphology and voltage loss of high-performance solar cells

Abstract

With the rapid growth of power conversion efficiency (PCE) of organic solar cells (OSCs) based on polymer donors (PDs) and small molecule acceptors (SMAs), it is of great interest to find an optimal combination of PD and SMA mediated by favorable donor/acceptor (D/A) interaction. To address this important issue, here we investigated the effects of the PD/SMA pairing in terms of fine-chlorination of non-conjugated phenoxyl units in side chain of the newly developed SMA series on the blend morphology, the interfacial molecular interactions, and the resulting photovoltaic properties. Our investigation was conducted with the four SMAs, named A1, A2, A3, and A4, having different inner side-chains and terminal groups. And the PD, named PBDT-Cl, was paired with the SMAs. As a result, we demonstrate that the terminal chlorine atom of side chain placed on the non-conjugated position can significantly affect to the enhanced interfacial interactions, the blend morphology (miscibility and crystallinity) with PD, and reduced voltage loss, resulting improved PCEs of the OSCs. Particularly, the devices based on the PBDT-Cl:A3 pairs showed the highest PCE of 17.19%.