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

Abstract

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 servemore » 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.« less

Authors:

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]

---

+ Show Author Affiliations

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)

Publication Date:

Mon Jun 27 00:00:00 EDT 2016

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Center for Energy Efficient Materials (CEEM)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); Ministry of Science and Technology (MOST) (Taiwan)

OSTI Identifier:

1369749

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

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 8; Journal Issue: 28; Related Information: CEEM partners with the University of California, Santa Barbara (lead); Purdue University; Los Alamos National Laboratory; National Renewable Energy Laboratory; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

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