Rational Molecular Design of Nonfullerene Acceptors for Bulk Heterojunction Solar Cells

Abstract

Organic photovoltaics (OPVs) have received considerable attention as clean energy conversion devices because of their lightweightness, cost effectiveness, flexibility, and suitability for roll-to-roll printing. In the past few decades, the active layer of OPV devices has usually consisted of conjugated polymers as donors and fullerene derivatives as acceptors, which typically form a bulk heterojunction (BHJ) structure.1,2 The power conversion efficiency (PCE) of OPVs based on fullerene derivative acceptors has reached over 10%. However, it is difficult to further increase the PCE of fullerene-based OPVs due to their inherent limitations including arduous energy-level tunability and low absorption profile. To enhance the photovoltaic performance of OPVs, nonfullerene acceptors (NFAs) with aromatic fused-ring structures have been extensively developed in recent years to fabricate high-efficiency OPVs. Compared to traditional fullerene acceptors, NFAs possess several advantages, such as facile synthesis and high absorption profile. Most high-performance NFAs possess acceptor-donor-acceptor (A-D-A) type structures, in which fused multi-ring ladder structures are used as the D unit and 1,1-dicyanomethylene-3-indanone (IC) derivatives as the A unit.In this talk I will give an overview of our recent studies on novel nonfullerene acceptors. In paticular, several nonfullerene acceptors possessing different D units have been designed and synthesized to address the relationship between the structure and the photophysical and photovoltaic properties of the A-D-A type nonfullerene acceptors.3,4 [1] T. Umeyama and H. Imahori, J. Mater. Chem. A (Feature Article), 2, 11545-11560 (2014).[2] T. Umeyama and H. Imahori, Acc. Chem. Res. 52, 2046-2055 (2019).[3] T. Umeyama, K. Igarashi, D. Sasada, Y. Tamai, K. Ishida, T. Koganezawa, S. Ohtani, K. Tanaka, H. Ohkita, and H. Imahori, Chem. Sci., 11, 3250-3257 (2020).[4] T. Umeyama, K. Igarashi, D. Sasada, K. Ishida,T. Koganezawa, S. Ohtani, K. Tanaka, and H. Imahori, ACS Appl. Mater. Interfaces, 12, 39236-39244 (2020).