Fluorinated naphtho[1,2-c:5,6-c\u2019]bis[1,2,5]thiadiazole-containing \u03c0-conjugated compound: synthesis, properties, and acceptor applications in organic solar cells

Shreyam Chatterjee,Yoshio Aso,Paul W M Blom,Yutaka Ie,Gert-Jan A H Wetzelaer,Takuji Seo,Taichi Moriyama

doi:10.1038/s41427-018-0088-4

Abstract

The incorporation of electron-accepting units into π-conjugated systems is well-established as a powerful approach to tune the physical properties and frontier orbital energy levels of molecules. To realize semiconductors with novel functions, naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole (NTz) has been utilized as an effective electron-accepting unit. To enhance the electron-accepting nature of NTz in this work, the synthesis of fluorinated naphthobisthiadiazole (FNTz) was accomplished by the sequential introduction of amino functional groups into 1,5-difluoronapthalene derivatives to form fluorinated tetraaminonapthalene derivatives, followed by the formation of thiadiazole rings. Organic solar cells based on our synthesized FNTz acceptor in combination with poly(3-hexylthiophene) (P3HT) as a donor exhibit a significant improvement of power conversion efficiency (PCE) compared to the corresponding nonfluorinated NTz-based cells, reaching a high PCE of up to 3.12%. Investigation of the blend-film properties and device physics unambiguously reveals that the blend films based on P3HT and the FNTz-based compound shows good film morphologies and thus efficient charge generation and transport characteristics. These results demonstrate the potential of FNTz for an electron-accepting unit in organic semiconductors.

Highlights

Introduction πConjugated systems have established indispensable positions as semiconducting materials in organic electronics, such as organic light-emitting diodes, fieldeffect transistors, and organic solar cells (OSCs).[1]
The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) orbitals are localized in the central parts, while the HOMO-1, HOMO-2, LUMO + 1, and LUMO + 2 orbitals are localized in the terminal units
Organic solar cells based on the synthesized acceptors and P3HT as a donor showed that fluorinated naphthobisthiadiazole (FNTz)-Teh-fluoranthene imide (FA) has superior performance to NTz-Teh-FA, and a power conversion efficiency (PCE) up to 3.12% was attained

Summary

Introduction

Introduction πConjugated systems have established indispensable positions as semiconducting materials in organic electronics, such as organic light-emitting diodes, fieldeffect transistors, and organic solar cells (OSCs).[1]. Selective injection and transportation of holes and/or electrons can be achieved, which is essential for the realization of such organic devices.[2,3,4,5] In this context, it is generally recognized that the incorporation of an electron-accepting unit into the π-conjugated system is an effective approach to tune the HOMO and LUMO energy levels. Given that effective electron-accepting units are still limited,[6,7,8,9,10,11] the creation of novel electronaccepting units is strongly needed to boost the development of high-performance organic semiconductors. Naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole (NTz), a doubly 2,1,3-benzobisthiadiazole (BTz)-fused heteroaromatic molecule, has been known to function effectively as an electron-accepting unit of donor–acceptor type donor copolymers for bulk-heterojunction OSCs (Fig. 1).[12,13,14,15,16]

Methods

Results

Conclusion