Development of non-fullerene small-molecule acceptor for efficient poly(3-Hexylthiophene)-based organic solar cell

Abstract

The organic solar cells (OSCs) have received great attention as renewable energy conversion devices owing to the solution processability, low-cost and light weight. Recently, the development of non-fullerene small molecule acceptors (NFSMAs) have improved power conversion efficiencies (PCEs) up to 18%. However, most high-performing polymer donors (P$_D$) feature complicated molecular structure and thus, it requires multi-synthetic steps and low yield impeding the roll-to-roll process for the large arear of OSCs. Furthermore, since the cross-coupling mechanism for high-performing P$_D$s is a step-wise poly condensation, it possesses difficulty to control the molecular weight and poly diversity index (PDI) resulting in unreliable OSC devices. In this respect, the poly(3-hexylthiophene) (P3HT) is one of the commercially viable P$_D$. Compared to traditional P$_D$, the P3HT prepared by chain-growth polymerization easily modulates the molecular weight and controls batch-to-batch variation. And also, the development of NFSMAs to be paired with P3HT have significantly enhanced PCE of P3HT based OSC up to 9%. Despite of successful enhancement in PCE, a designing NFSMA realizing high-performances and thermal stability have been considered as challenging issues.Especially, the NFSMAs have limited to possess high performances and thermal stability in the P3HT blend system. For example, non-oriented crystallites of the NFSMAs easily undergo re-oriented and re-crystallization under thermal stress due to their low low-glass transition temperatures (T$_g$s), resulting in degradation of OSC performances. Whereas, the fullerene-based acceptors easily secure the micro crystal structure by post-thermal treatment possessing high-electrical properties, the weak pi-pi interactions of NFSMA backbones lead difficulty to secure crystallinity in the P3HT blend. Accordingly, we designed and synthesized non-covalently fused ring acceptors for realizing efficient and thermally stable P3HT-based OSCs. In these contributions, we believe these works will provide important evidence the for commercialization of OSCs and the development of NFSMAs.