Article Cite This: Chem. Mater. XXXX, XXX, XXX−XXX
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Multiple Fused Ring-Based Near-Infrared Nonfullerene Acceptors with an Interpenetrated Charge-Transfer Network Jianfei Qu,† Qiaoqiao Zhao,† Jiadong Zhou,‡ Hanjian Lai,† Tao Liu,† Duning Li,† Wei Chen,*,§,∥ Zengqi Xie,*,‡ and Feng He*,†
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Department of Chemistry and Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055, China ‡ Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China § Materials Science Division, Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States ∥ Institute for Molecular Engineering, The University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, United States S Supporting Information *
ABSTRACT: Two small molecule acceptors with chlorinated IC as end groups and 10-ring- and 12-ring-fused cores as central units, named R10-4Cl and R12-4Cl, were designed and synthesized, which exhibit low optical band gaps of 1.43 and 1.35 eV, respectively. X-ray crystallographic analysis of R104Cl shows that the end groups of adjacent molecules are parallel and partially overlap with a short π−π distance of 3.32 Å, which is helpful for electron transport in this direction. At the same time, there is another type of molecular orientation that lies in these two molecules with an angle about 64.7° because of the close contact of S···O with a distance of 3.15 Å. The two types of molecular arrangements result in an interpenetrated network structure in R10-4Cl films, which is helpful for the rapid charge transfer either along the horizontal direction or the sloping direction. After blending with a PBDB-T polymer donor, the R10-4Cl-based device shows wide photocurrent response from the visible to near-infrared regions, resulting in the better usage of the sunlight source. Benefited from this comprehensive solar energy absorption and the interpenetrated charge transfer, the R10-4Cl-based devices show a power conversion up to 10.7% with an improved JSC of 18.9 mA cm−2.
1. INTRODUCTION Bulk heterojunction organic solar cells (OSCs) consisting of electron-donor and electron-acceptor materials have shown great potential as new energy sources because of their low cost, lightweight, and flexibility.1−4 In the past, fullerene derivatives (such as PC61BM and PC71BM) played indispensable roles in the development of OSCs.5−10 The power conversion efficiency (PCE) of OSCs based on fullerene derivatives exceeded 11%.11,12 However, because of their intrinsic drawbacks, such as weak absorption in the visible and nearinfrared (NIR) region, energy levels that are difficult to regulate, and difficulty of preparation and purification, fullerene derivative-based OSCs are difficult to improve.9,13−15 In comparison, nonfullerene acceptors show many advantages, for instance, simple synthesis and purification, easily adjusted energy levels, and strong absorption in the visible and NIR region.13,16−20 Among them, A−D−A-type small molecule acceptors, such as ITIC with indacenodithieno[3,2-b]thiophene as the central donor unit and 2-(3-oxo-2,3dihydroinden-1-ylidene)malononitrile (IC) as the electronwithdrawing unit, and their analogues, are the most widely used nonfullerene acceptors.21−24 The PCEs of single-junction © XXXX American Chemical Society
OSCs have exceeded 13% through molecular engineering and device optimization.25−33 NIR-absorbing materials are greatly desirable because of the broadened photocurrent response region after blending with wide band gap donor materials, which are beneficial for achieving higher short-circuit current density (JSC); indeed, they are desirable for semitransparent OSCs, ternary OSCs, and tandem OSCs.34−43 A−D−A-type small molecules can easily achieve narrow band gaps (
