Cofacial Versus Coplanar Arrangement in Centrosymmetric Packing Dimers of Dipolar Small Molecules: Structural Effects on the Crystallization Behaviors and Optoelectronic Characteristics
- National Taiwan Univ., Taipei (Taiwan)
- National Tsing Hua Univ., Hsinchu (Taiwan)
- National Chiao Tung Univ., Hsinchu (Taiwan)
- Univ. of California, Santa Barbara, CA (United States)
- Inst. of Nuclear Energy Research, Taoyuan (Taiwan)
- Academia Sinica, Taipei (Taiwan)
Two D-π–A-A molecules (MIDTP and TIDTP) composed of an electron-rich ditolylamino group (D) and an electron-deficient 5-dicyanovinylenylpyrimidine (A-A) fragment bridged together with indeno[1,2-b]thiophene (IDT) were synthesized. These molecules provide an opportunity to examine in-depth the impact of side-chain variations (methyl vs p-tolyl) on the crystallization behaviors, solid-state morphology, physical properties, and optoelectronic characteristics relevant for practical applications. X-ray analyses on single-crystal structures indicate that methyl-substituted MIDTP forms “coplanar antiparallel dimers” via C–H···S interactions and organizes into an ordered slip-staircase arrays. In contrast, p-tolyl-bearing TIDTP shows “cofacial centrosymmetric dimers” via π–π interactions and packs into a less-ordered layered structures. The X-ray diffraction analyses upon thermal treatment are consistent with a superior crystallinity of MIDTP, as compared to that of TIDTP. This difference indicates a greater propensity to organization by introduction of the smaller methyl group versus the bulkier p-tolyl group. The increased propensity for order by MIDTP facilitates the crystallization of MIDTP in both solution-processed and vacuum-deposited thin films. MIDTP forms solution-processed single-crystal arrays that deliver OFET hole mobility of 6.56 × 10–4 cm2 V–1 s–1, whereas TIDTP only forms amorhpous films that gave lower hole mobility of 1.34 × 10–5 cm2 V–1 s–1. MIDTP and TIDTP were utilized to serve as donors together with C70 as acceptor in the fabrication of small-molecule organic solar cells (SMOSCs) with planar heterojunction (PHJ) or planar-mixed heterojunction (PMHJ) device architectures. OPV devices based on higher crystalline MIDTP delivered power conversion efficiencies (PCEs) of 2.5% and 4.3% for PHJ and PMHJ device, respectively, which are higher than those of TIDTP-based cells. Finally, the improved PCEs of MIDTP-based devices are attributed to better hole-transport character.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Center for Energy Efficient Materials (CEEM)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES); Ministry of Science and Technology (MOST) (Taiwan)
- Grant/Contract Number:
- SC0001009; 104-2628-E-009-007- MY3; 104-2633-M-007-001; 101-2113-M-002-009-MY3; NSC-102-2917-I-002-103
- OSTI ID:
- 1369749
- Journal Information:
- ACS Applied Materials and Interfaces, Vol. 8, Issue 28; Related Information: CEEM partners with the University of California, Santa Barbara (lead); Purdue University; Los Alamos National Laboratory; National Renewable Energy Laboratory; ISSN 1944-8244
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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