Cofacial Versus Coplanar Arrangement in Centrosymmetric Packing Dimers of Dipolar Small Molecules: Structural Effects on the Crystallization Behaviors and Optoelectronic Characteristics

Journal Article · Mon Jun 27 00:00:00 EDT 2016 · ACS Applied Materials and Interfaces

DOI:https://doi.org/10.1021/acsami.6b03371· OSTI ID:1369749

Chou, Shu-Hua ^[1]; Kang, Hao-Wei ^[2]; Chang, Shu-Ting ^[3]; Wu, Kuan-Yi ^[3]; Bazan, Guillermo C. ^[4]; Wang, Chien-Lung ^[3]; Lin, Hong-Lin ^[2]; Chang, Jung-Hao ^[2]; Lin, Hao-Wu ^[2]; Huang, Yu-Ching ^[5]; Tsao, Cheng-Si ^[5]; Wong, Ken-Tsung ^[6]

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1. National Taiwan Univ., Taipei (Taiwan)
2. National Tsing Hua Univ., Hsinchu (Taiwan)
3. National Chiao Tung Univ., Hsinchu (Taiwan)
4. Univ. of California, Santa Barbara, CA (United States)
5. Inst. of Nuclear Energy Research, Taoyuan (Taiwan)
6. 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)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
organic solar cell
planar-mixed heterojunction
organic field effect transistors
push−pull molecules
substitution effect
crystallinity