Electron-to Hole Transport Change Induced by Solvent Vapor Annealing of Naphthalene Diimide Doped with Poly(3-Hexylthiophene).

Krzysztof Janus,Kinga Danielewicz,Adam Kiersnowski,Dorota Chlebosz,Waldemar Goldeman

doi:10.3389/fchem.2021.703710

Abstract

Herein we report on fabrication and properties of organic field-effect transistors (OFETs) based on the spray-coated films of N,N′-dioctyl naphthalene diimide (NDIC8) doped with 2.4 wt% of poly (3-hexylthiophene) (P3HT). OFETs with the untreated NDIC8:P3HT films revealed electron conductivity [μe* = 5 × 10–4 cm2×(Vs)−1]. After the annealing in chloroform vapor the NDIC8:P3HT films revealed the hole transport only [μh* = 0.9 × 10–4 cm2×(Vs)−1]. Due to the chemical nature and energy levels, the hole transport was not expected for NDIC8-based system. Polarized optical- and scanning electron microscopies indicated that the solvent vapor annealing of the NDIC8:P3HT films caused a transition of their fine-grained morphology to the network of branched, dendritic crystallites. Grazing incidence wide-angle X-ray scattering studies indicated that the above transition was accompanied by a change in the crystal structure of NDIC8. The isotropic crystal structure of NDIC8 in the untreated film was identical to the known crystal structure of the bulk NDIC8. After the solvent annealing the crystal structure of NDIC8 changed to a not-yet-reported polymorph, that, unlike in the untreated film, was partially oriented with respect to the OFET substrate.

Highlights

Scalable wet deposition technologies, such as spray-coating, gravure, slot-die coating, meniscusguided coating etc. are considered amongst the most important, technologically-relevant strategies of fabrication of organic, thin-film based electronic devices (Hwang, Bae, and Kim 2014; Koutsiaki et al, 2019; Chen et al, 2020; Chaturvedi et al, 2021; Michels et al, 2021)
The solvent vapor annealing of NDIC8 caused a reduction of the μe down to 0.25 × 10–4 cm2×(Vs)−1, which we have attributed to dewetting of the film, coarsening of the crystal morphology
Our study demonstrates that unlike in the case of p-type polymers, charge carrier transport in n-type materials, such as naphthalene diimides (NDIC8 here), cannot be enhanced by doping with small amounts of p-type polymers (P3HT here)

Summary

Introduction

Scalable wet deposition technologies, such as spray-coating, gravure, slot-die coating, meniscusguided coating etc. are considered amongst the most important, technologically-relevant strategies of fabrication of organic, thin-film based electronic devices (Hwang, Bae, and Kim 2014; Koutsiaki et al, 2019; Chen et al, 2020; Chaturvedi et al, 2021; Michels et al, 2021). Are considered amongst the most important, technologically-relevant strategies of fabrication of organic, thin-film based electronic devices (Hwang, Bae, and Kim 2014; Koutsiaki et al, 2019; Chen et al, 2020; Chaturvedi et al, 2021; Michels et al, 2021). Formation of the solid films upon any wet deposition process can be considered a problem of a crystallization of solution components at the solid surface. Electronic devices based on binary blends may reveal unique properties due to doping or formation of phase separated morphologies with desired architecture (Sepe et al, 2014; Afraj et al, 2021). Control over formation of BHJ can be used to tailor properties of light-emitting diodes and photovoltaics or achieving balanced transport of electrons or holes in ambipolar organic field-effect transistors (OFETs)

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