Molecular Engineering of Highly Efficient Small Molecule Nonfullerene Acceptor for Organic Solar Cells

Abstract

A new molecularly engineered nonfullerene acceptor, 2,2′‐(5,5′‐(9,9‐didecyl‐9H‐fluorene‐2,7‐diyl)bis(benzo[c][1,2,5]thiadiazole‐7,4‐diyl)bis(methanylylidene))bis(3‐hexyl‐1,4‐oxothiazolidine‐5,2‐diylidene))dimalononitrile (BAF‐4CN), with fluorene as the core and arms of dicyano‐n‐hexylrhodanine terminated benzothiadiazole is synthesized and used as an electron acceptor in bulk heterojunction organic solar cells. BAF‐4CN shows a stronger and broader absorption with a high molar extinction coefficient of 7.8 × 104m−1 cm−1 at the peak position (498 nm). In the thin film, the molecule shows a redshift around 17 nm. The photoluminescence experiments confirm the excellent electron accepting nature of BAF‐4CN with a Stern–Volmer coefficient (Ksv) of 1.1 × 105m−1. From the electrochemical studies, the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of BAF‐4CN are estimated to be −5.71 and −3.55 eV, respectively, which is in good synchronization with low bandgap polymer donors. Using BAF‐4CN as an electron acceptor in a poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3″′‐di(2‐octyldodecyl) 2,2′;5′,2″;5″,2″′‐quaterthiophen‐5,5″′‐diyl)] based bulk‐heterojunction solar cell, a maximum power conversion efficiency of 8.4% with short‐circuit current values of 15.52 mA cm−2, a fill factor of 70.7%, and external quantum efficiency of about 84% covering a broad range of wavelength is achieved.

Recent Advances in Nonfullerene Acceptors for Organic Solar Cells

“…Therefore, it is necessary to find new methods to increase the electron mobility and to suppress the recombination loss, for example, through the design of novel acceptor molecule, the optimization of the film morphology and the engineering of the donor and acceptor interfacial structure for obtaining the high efficiency nonfullerene OSCs, which is mentioned in the challenge and opportunity section. Moreover, with the unremitting efforts on developing the more efficient nonfullerene acceptors and further explicating the relationships between the structure and property, even high efficiency nonfullerene OSCs can be obtained in the near future and the nonfullerene acceptors can possess the strong competitiveness with their fullerene portion …”

“…Moreover, with the unremitting efforts on developing the more efficient nonfullerene acceptors and further explicating the relationships between the structure and property, even high efficiency nonfullerene OSCs can be obtained in the near future and the nonfullerene acceptors can possess the strong competitiveness with their fullerene portion. [68,97,172,192,257,[326][327][328][329][330] The development of OSCs results in explosion of materials, data, and remarkable advances in term of efficiencies. Consequently, many groups all over the world involved in this field face strong and growing international competition that gave rise to, what we call, the "fury race to efficiencies."…”

A Halogenation Strategy for over 12% Efficiency Nonfullerene Organic Solar Cells

“…acceptor end-groups, [12,13,15,[28][29][30][31][32][33][34][35][36] aiming to tune the energy levels, absorption, and even packing modes in the active layers. In contrast to the various core units for the A-D-A-type NFAs, only a few endgroups such as 2-(2,3-dihydro-3-oxo-1Hinden-1-ylidene)propanedinitrile (INCN) and rhodanine and their derivatives have been reported.…”

A Highly Planar Nonfullerene Acceptor with Multiple Noncovalent Conformational Locks for Efficient Organic Solar Cells

“…To probe the quenching efficiency of PBDB‐T with IDT‐4CN or PC 71 BM, the photoluminescence (PL) measurements were performed in CB solution. As shown in Figure S5 (Supporting Information), the PL intensity of PBDB‐T was gradually decreased with increasing IDT‐4CN or PC 71 BM content, and the Stern–Volmer quenching coefficient ( K sv ) was calculated by the following equationwhere η 0 and η are the PL intensity in absence and presence of acceptor, respectively, and c is the acceptor concentration. Figure showed the Stern–Volmer quenching plot as a function of acceptor concentration.…”

“…To probe the quenching efficiency of PBDB-T with IDT-4CN or PC 71 BM, the photoluminescence (PL) measurements were performed in CB solution. As shown in Figure S5 the Stern-Volmer quenching coefficient (K sv ) was calculated by the following equation [40] K c 1 0 sv…”