Small molecular non-fullerene acceptors based on naphthalenediimide and benzoisoquinoline-dione functionalities for efficient bulk-heterojunction devices

Through the conjunction of naphthalenediimide and benzoisoquinoline-dione functionalities, two novel, solution-processable non-fullerene electron acceptors, 2,7-dioctyl-4,9-bis(2-octyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (coded as NDI-N1) and 2,7-dioctyl-4,9-bis(5-(2-octyl-1,3-dioxo-2,3-dihydro-1H-benzo[de] isoquinolin-6-yl)thiophen-2-yl)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)-tetraone (coded as NDI-N2), were designed, synthesized, and used as active components for bulk-heterojunction photovoltaic devices. The new chromophores were based on the acceptor–acceptor–acceptor module where naphthalenediimide unit served as the central acceptor flanked by terminal benzoisoquinoline-dione acceptor functionality. The optoelectronic and photovoltaic properties of NDI-N1 and NDI-N2 were directly compared. Solution-processable bulk-heterojunction devices were fabricated using NDI-N1 and NDI-N2 as non-fullerene electron acceptor materials. Studies on the photovoltaic properties revealed that the best poly(3-hexylthiophene) (P3HT): NDI-N2-based device showed an impressive enhanced power conversion efficiency of 4.04%, around 40% increase with respect to the efficiency of the best NDI-N1-based device (2.91%). It is justifiable to mention that the device outcome reported herein provides strong support and incentive for the current research strategy, and that the conjoint use of potential acceptor building blocks, such as naphthalenediimide and benzoisoquinoline-dione, can indeed generate efficient non-fullerene acceptors.