Enhancing the Photovoltaic Performance of Nonfullerene Acceptors via Conjugated Rotatable End Groups

Abstract

AbstractUnlike varieties of well‐known nonfullerene acceptors with rigid chemical structures, an acceptor–donor–acceptor (A–D–A)‐type acceptor with conjugated rotatable end groups, a phenylethynyl‐substituted acceptor (ITPN) is designed and synthesized. Compared with the ethynyl‐substituted acceptor (ITEN) and a well‐know small molecular electron acceptor (ITIC), ITPN molecules show reduced binding energy and reorganization energy, facilitated by the rotatability and the extended π conjugation of phenylethynyl end groups. ITPN shows stronger molecular aggregation and more ordered arrangement, resulting in enhanced charge‐transport properties. In the polymer solar cells, applying the fluorinated polymer (PBDB‐TF) as the electron donor, the device based on ITPN yields a maximum power conversion efficiency of 12.6%, higher than that of an ITEN‐ or ITIC‐based device. The work demonstrates that chemically modulating the end groups by the synergistic effect of rotatable end groups and extending the π‐conjugation length is an effective and straightforward way to improve the photovoltaic performance of A–D–A‐type small molecular acceptors.