Elsevier

Dyes and Pigments

Volume 174, March 2020, 108014
Dyes and Pigments

Perylene-diimide-based n-type semiconductors with enhanced air and temperature stable photoconductor and transistor properties

https://doi.org/10.1016/j.dyepig.2019.108014Get rights and content

Highlights

  • Perylene-diimide-based acrylate monomer and polymer n-type organic semiconductors are synthesized.

  • Monomer and polymer transistors exhibit pure n-type transport with mobility of 10-5 cm2·V-1·s-1 for polymer devices.

  • When integrated into a photovoltaic architecture, photocurrent to dark current ratios of up to 103 were realized.

  • Annealing in ambient atmosphere improved the air and temperature stability of perylene-diimide-based polymer devices.

Abstract

We report the synthesis and characterization of highly air and temperature stable, solution-processed, n-type organic semiconductors: a perylene-diimide monomer and a perylene-diimide-based pendant polymer. When integrated into a transistor structure, both materials possess pure n-type transport with mobility as high as 10−5 cm2 V−1 s−1 for the polymer. The organic semiconductors exhibit good photoconductor properties, with photocurrent to dark current ratios of up to 103 for the monomer, despite its lower FET mobility. The differences in transistor and photoconductor properties suggest different applications for each material. Both materials can be processed in air, and their transport properties have good air stability, improving with annealing even up to 200 °C in air. It is notable that such air-stable photoconductivity and transport properties have rarely been reported for n-type organic semiconductors before, as most n-type organic semiconductors are not stable in air. Hence, these materials may have potential in a wide range of applications.

Introduction

Solution-processible organic semiconductors offer potentially inexpensive active components in large area electronics as complementary circuits (CMOS), field effect transistors (FETs), radio-frequency ID tags, sensors, organic light-emitting diodes (OLEDs), and photovoltaics (OPVs) [1]. Remarkable progress has been achieved for hole-transporting (p-type) polymer semiconductors with mobilities exceeding 35 cm2 V−1s−1 and with good air and thermal stability [[2], [3], [4]] – suitable for the above mentioned applications. In contrast, the development of stable, purely electron transporting (n-type) materials with good transport properties, and even more importantly, good air and thermal stability [5,6] remains a critical need in the field, as stable, high performance n-type semiconductors are essential for the development of organic CMOS integrated circuits and the expansion of electron accepting materials for organic photovoltaics. With current n-type conjugated materials, the formation of free electrons along the conjugated bond results in the geometric distortion of the bond and the formation of an unstable radical charge [7]. Hence, they are typically energetically unfavorable. Fortunately, n-type charge formation can be stabilized via conjugated donor-acceptor interactions, and strong n-type transport behavior has been reported for donor-acceptor type conjugated organic semiconductors [8,9]. However, these donor-acceptor conjugated semiconductors typically have commensurate p-type transport with varying degrees of strength. For many applications, the simultaneous presence of p-type transport may constitute a problem. For FETs, the presence of p-type transport in an n-type transistor will lead to a lack of, or limited range of, an OFF state. For OPVs, p-type transport states in the n-type region of an organic solar cell will serve as hole-traps and exciton-recombination sites, reducing the photo-performance of the device.

Perylene-diimides (PDIs) are highly electron-deficient conjugated structures that can exist stably in ambient environments, enabling their application as dyes [10,11]. This electron-deficiency, together with strong intermolecular π- π coupling, results in good n-type transport in well-ordered films of suitably deposited variants of PDI molecules, thereby allowing for numerous electronic applications [[12], [13], [14], [15]]. PDI-based pendant polymers have been synthesized via “click” [16,17] and nitroxide radical mediated routes [18], and these polymers have exhibited good electron mobility in organic field effect transistors [19]. In particular, PDIs are attractive candidates for n-type active materials for organic solar cells [20]; furthermore, the design space for PDI-based organic electronics has expanded via advances in both molecular and device architectures [[21], [22], [23], [24], [25]]. In this paper, we report on the photoconductive properties of a monomer and a pendant polymer, both consisting of PDI with an acrylate-based swallow-tail side-group [26,27]. Devices that we fabricated under ambient conditions showed good transistor and photoconductor performance in air. More significantly, transport properties improved with annealing up to 200 °C in air. The results indicate good environmental stability for these types of PDI organic semiconductors and bodes well for a variety of applications.

Section snippets

Materials

All starting materials and solvents were obtained from Sigma-Aldrich (St. Louis, MO, USA) and were used as received. The synthesis of the PDI monomer and PDI polymer is described herein:

Synthesis of perylene-diimide monomer and pendant polymer

Synthesis of the PDI monomer and PDI polymer is illustrated in Scheme 1. The synthesis of the starting unsymmetric perylene mono-imide mono-anhydride molecule (1) was modified from previous report by Mery et al. [27] The synthesis of the PDI monomer and pendant polymer was modified from previous reports by Haberkorn et al. and Kota et al. [32,33] Starting molecule yields were good (≈90%) for compounds 1 and 2, while moderate yields 50% for hydrolysis into monomer (3) and 60% yield for

Conclusion

In conclusion, we have synthesized two PDI-based materials–a monomer and a pendant polymer. Both materials are solution-processible, have n-type transistor properties and are stable up to 200 °C in air (with additional TGA and DSC data available in ESI). We show through a series of analyses—UV-Vis, electrochemical, photoconductivity and transistor measurements on solution processed films of both materials—that the transport properties of the PDI polymer are better than those of the monomer. We

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was funded by the Naval Research Laboratory (NRL) and Office of Naval Research (ONR) 6.1 work unit MA041–06–41–9899 and the Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST), a Nano-Systems Engineering Research Center funded by the National Science Foundation (EEC1160483). All high resolution mass spectrometry measurements were made in the Molecular Education, Technology, and Research Innovation Center (METRIC) at NC State University. The UV–Vis and PL

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