Tuning the ambipolar behaviour of organic field effect transistors via band engineering

P R Warren,M Riede,A E Lauritzen,J Nelson,J F M Hardigree

doi:10.1063/1.5080505

P R Warren, M Riede + Show 3 more

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https://doi.org/10.1063/1.5080505

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Journal: AIP Advances	Publication Date: Mar 1, 2019
Citations: 21	License type: cc-by

Affiliation: University of Oxford, Imperial College London

Abstract

We report on a method for fabricating balanced hole and electron transport in ambipolar organic field-effect transistors (OFETs) based on the co-evaporation of zinc-phthalocyanine (ZnPc) and its fluorinated derivative (F8ZnPc). The semiconducting behaviour of the OFET can be tuned continuously from unipolar p-type, with a hole mobility in the range of (1.7 ± 0.1) × 10−4 cm2/Vs, to unipolar n-type, with an electron mobility of (1.0 ± 0.1) × 10−4 cm2/Vs. Devices of the pristine ZnPc and F8ZnPc show a current on/off ratio of 105. By co-evaporating the p-type ZnPc with the n-type F8ZnPc, we fabricate ambipolar transistors and complementary-like voltage inverters. For the ambipolar devices, the optimum balance between the hole and electron mobilities is found for the blend of 1:1.5 weight ratio with hole and electron mobilities of (8.3 ± 0.2) × 10−7 cm2/Vs and (5.5 ± 0.1) × 10−7 cm2/Vs, respectively. Finally we demonstrate application of the ambipolar devices in a complementary-like voltage inverter circuit with the performance comparable to an inverter based on separate ZnPc and F8ZnPc OFETs.

Highlights

Organic semiconductors are of great interest for use in electronics
We report on a method for fabricating balanced hole and electron transport in ambipolar organic field-effect transistors (OFETs) based on the co-evaporation of zinc-phthalocyanine (ZnPc) and its fluorinated tuned continuously from unipolar p-type, with a hole mobility in the draenrigveatoifve(1(.F78±Zn0P.1c)).×T1h0e−s4ecmmic2o/Vnds,utcotiunngibpeohlaarvnio-utyrpoef,twheithOaFnETeleccatnrobne mobility of (1.0 ± 0.1) × 10−4 cm2/Vs
We report a method for fabricating ambipolar OFETs with balanced hole and electron transport based on the co-evaporation of ZnPc and its fluorinated derivative F8ZnPc

Summary

INTRODUCTION

Organic semiconductors are of great interest for use in electronics. They combine semiconducting properties with established processing techniques like vacuum and solution coating, which require only low substrate temperatures allowing for deposition on flexible, large-area substrates. Ambipolar semiconductors, which allow for both polarities of charge to be induced in an OFET, offer an alternative design known as complementary-like logic.7 In this scheme, ambipolar OFETs replace both the p- and n-type transistors circumventing the advanced patterning techniques necessary to deposit two separate materials, simplifying the fabrication process. The step-like shift in ionisation potential (IP) by fluorination resulted in a smaller Schottky barrier for electron injection at the organic-gold contacts such that ambipolar behaviour was observed for F4ZnPc and n-type behaviour for both F8ZnPc and F16ZnPc. In this study, we co-evaporate films of ZnPc and F8ZnPc (chemical structures shown in Figure 1) over a range of blend weight ratios to overcome the limitations of only having discrete energy steps given by the fluorination. We demonstrate the ambipolar OFETs in a complementarylike voltage inverter

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSION