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Synthesis, Property, and Optoelectronic Device Application of Bis-Lactam-Based Organic Semiconducting Materials : 비스락탐을 기반으로 한 유기반도체 물질의 합성, 특성 및 광전자 소자 응용에 대한 연구
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- Authors
- Advisor
- 박수영
- Major
- 공과대학 재료공학부
- Issue Date
- 2017-08
- Publisher
- 서울대학교 대학원
- Keywords
- organic semiconductor ; organic field-effect transistors (OFETs) ; organic solar cells (OPVs)
- Description
- 학위논문 (박사)-- 서울대학교 대학원 공과대학 재료공학부, 2017. 8. 박수영.
- Abstract
- Organic semiconductors have attracted great attention in the last decade because of their promising potential as materials for advanced optoelectronic devices. Among organic semiconductors, those based on bis-lactam materials, such as diketopyrrolopyrrole (DPP), isoindigo (II), isoDPP, and thienoisoindigo (TII), have been extensively studied as desirable electron-withdrawing building blocks, because of their unique features, which include (a) a high electron affinity because of the electron-withdrawing effect of the lactam units
(b) a high degree of π-π stacking, deriving from their quasi-planar backbone structure
and (c) the possibility of controlling their solubility by incorporation of suitable alkyl and aryl side chains at the lactam N-atom position. Hence, I studied the bis-lactam-based semiconducting materials as electron-deficient building blocks for high-performance organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). In this thesis, I have designed and synthesized three different kinds of novel bis-lactam-based semiconducting materials by modifying their structures, and then investigated their structure-property relationships.
First, a new high-performance small molecular n-channel semiconductor based on diketopyrrolopyrrole (DPP), DPP-T-DCV was designed and synthesized. The frontier molecular orbitals have been engineered by introducing a strong electron-accepting dicyanovinyl group. The well-defined lamellar structure of the DPP-T-DCV crystal displayed a uniform terrace step height corresponding to a molecular monolayer in the solid-state. As a result of the high level of crystallinity derived from the conformational planarity, OFETs made of dense-packed solution-processed single-crystals of DPP-T-DCV exhibited an electron mobility up to 0.96 cm2 V–1 s–1, one of the highest values yet obtained for DPP derivative-based n-channel OFETs. Polycrystalline OFETs also showed decent electron mobility of 0.64 cm2 V–1 s–1 suitable for practical device applications. (Chapter 2)
Second, a novel electron-accepting bis-lactam building block, 3,7-dithiophen-2-yl-1,5-dialkyl-1,5-naphthyridine-2,6-dione (NTDT), and a conjugated polymer P(NTDT-BDT) comprising NTDT as an electron acceptor and benzo[1,2-b:4,5-b']dithiophene (BDT) as an electron donor have been designed and synthesized for producing efficient OPVs. The thermal, electronic, photophysical, electrochemical, and structural properties of NTDT and P(NTDT-BDT) have been studied in detail and compared with those of the widely used bis-lactam acceptor dithienyl-substituted-DPP (DPPT) and its polymer P(DPPT-BDT). Compared to DPPT derivatives, NTDT and P(NTDT-BDT) exhibited remarkably higher absorption coefficients, deeper highest occupied molecular orbital energy levels, and more planar structures. A bulk heterojunction solar cell based on P(NTDT-BDT) exhibited a power conversion efficiency of up to 8.16% with a short circuit current (Jsc) of 18.51 mA cm-2, one of the highest Jsc values ever obtained for BDT-based polymers. It was successfully demonstrated that the novel bis-lactam unit NTDT is a promising building block for use in OPVs. (Chapter 3)
Although the performance of the first successful NTDT-based OPVs, P(NTDT-BDT), was promising, it operated best only for medium-thick active-layer (≈ 140 nm) due to insufficient polymer crystallinity. Therefore, it was considered that the polymer crystallinity should be increased via backbone structure modification in order to produce more efficient (> 9% PCE) thick-active-layer (> 200 nm) OPVs. To this end, new semiconducting polymers, PNTDT-2T, PNTDT-TT, and PNTDT-2F2T, with NTDT as an acceptor, as well as 2,2'-bithiophene (2T), thieno[3,2-b]thiophene (TT) and 3,3'-difluoro-2,2'-bithiophene (2F2T) as donors were designed and synthesized. It was found that PNTDT-2F2T exhibited superior polymer crystallinity and a much higher absorption coefficient than those of PNTDT-2T or PNTDT-TT attributed to the appropriate matching between the highly coplanar acceptor (NTDT) and donor (2F2T) building blocks. A bulk heterojunction solar cell with a thick active layer (>200 nm) of PNTDT-2F2T simply fabricated without using post-fabrication hot processing, demonstrated an outstanding power conversion efficiency of up to 9.63%, with a short circuit current of 18.80 mA cm-2 and a fill factor of 0.70. (Chapter 4)
- Language
- English
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