Abstract
Conformational diversity due to different orientations of structural subunits has a complex impact on morphological disorder of organic semiconductors. Here, we isolate the impact of a specific structural change: replacing bithiophene (biTh) units with thieno[3,2-b]thiophene (TT). We compare four molecules with an alternating donor-acceptor structure (D′-A-D-A-D′) composed of a central, electron-rich dithienosilole (DTS) unit flanked by pyridyl-[2,1,3]thiadiazole (PT) or fluorinated benzo[c][1,2,5]thiadiazole (FBT) and end-capped with bithiophene biTh or TT groups. We find that using TT instead of biTh results in an increased degree of order within films cast directly from solution by influencing the self-assembly tendencies of the different molecules. Unlike switching the acceptor subunit, such as FBT for PT, the TT for biTh structural change has little impact on the electronic structure of these molecular semiconductors. Instead, these morphological effects can be understood within the context of the predicted conformational diversity. TT units limit the number of rotational conformations (rotamers) available within this molecular architecture; low rotamer dispersity facilitates self-assembly into ordered domains. As a practical illustration of this greater drive toward self-assembly, we use the TT-containing molecules as donors in bulk heterojunction solar cells with PC70BM. Devices with TT-containing molecules show improved photovoltaic performance compared to their previously characterized biTh analogs (d-DTS(PTTh2)2 and p-DTS(FBTTh2)2) in both as-cast and optimized conditions, with efficiencies up to 6.4% and 8.8% for PT-TT and FBT-TT, respectively. The TT subunit and, more broadly, the strategy of limiting conformational diversity can be readily applied toward the design of solution-processable organic semiconductors with increased as-cast order.
| Original language | English |
|---|---|
| Pages (from-to) | 383-394 |
| Number of pages | 12 |
| Journal | Journal of Materials Chemistry A |
| Volume | 6 |
| Issue number | 2 |
| DOIs | |
| State | Published - 2018 |
Bibliographical note
Publisher Copyright:© 2018 The Royal Society of Chemistry.
Funding
Research at UCSB was supported by the Office of Naval Research, ONR Awards No. N00014-14-1-0580, N00014-16-1-2520, and N00014-14-1-0101. C. M. thanks Dr Simon Teat, staff scientist of Beamline 11.3.1 at the ALS, for rening the FBT-TT crystal structure. GIWAXS measurements and single-crystal diffraction were carried out at Beamline 7.3.3 (ref. 76) and 11.3.1 of the Advanced Light Source, respectively, a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. KN, BY, and TG thank the UGC, New Delhi for providing research fellowships. SPS thanks nancial support from Indo-US BASE (Bhaskara Advanced Solar Energy) Fellowship program, Grant No. IUSSTF BASE Fellowship 2015/F-4 and from Indo-UK APEX project (Phase-II). RD thanks the UGC for the Junior Research Fellowship. The work at the University of Kentucky was supported by the Department of the Navy, Office of Naval Research, ONR Award No. N00014-16-1-2985. Supercomputing resources on the Lipscomb High Performance Computing Cluster were provided by the University of Kentucky Information Technology Department and Center for Computational Sciences (CCS).
| Funders | Funder number |
|---|---|
| DOE Office of Science User Facility | DE-AC02-05CH11231 |
| Department of the Navy | |
| Indo-US BASE | |
| Office of Naval Research Naval Academy | N00014-14-1-0101, N00014-16-1-2520, N00014-16-1-2985, N00014-14-1-0580 |
| University of California Santa Barbara | |
| University of Kentucky | |
| University of Kentucky Information Technology Department and Center for Computational Sciences | CCS |
| Indo-US Science and Technology Forum | 2015/F-4 |
| University Grants Commission | |
| Saudi Pharmaceutical Society |
ASJC Scopus subject areas
- General Chemistry
- Renewable Energy, Sustainability and the Environment
- General Materials Science
