Selective solution shearing deposition of high performance TIPS-pentacene polymorphs through chemical patterning
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Methods for the solution deposition of organic semiconductors (OSCs) show great potential for the production of large-area, inexpensive, and flexible organic electronics. A solution deposition method called solution shearing has consistently been shown to yield thin film transistors with improved performance over those created via other solution-based approaches. However, the need for discrete, electronically isolated devices requires the parallel development of a facile means of pattern definition compatible with the solution shearing process. In our work, we use a simple chemical prepatterning method to enable the solution shearing deposition of the small molecule OSC TIPS-pentacene on substrates with feature sizes as small as 100 lm. Grazing incidence x-ray diffraction (GIXD) was also used to confirm the existence of high performance TIPS-pentacene polymorphs in the patterned thin films. Mobilities as high as 1.13 cm2 V1 s1 were obtained on 400 lm wide patterns by depositing a high-performance, metastable polymorph of TIPS-pentacene.
I. INTRODUCTION
Transparent, flexible, low-cost, and large area printed electronics are highly anticipated for enabling the development of various applications, such as flexible electronic displays and low cost sensors.1–5 Thin film transistors (TFTs) are the basic building blocks of electronics, and in recent years it has been shown that high performance TFTs can be fabricated from small molecule organic semiconductors (OSCs).6–14 Solution-based methods of deposition for small molecule OSC thin films are desired for the high-throughput fabrication of low-cost, large-area devices. Currently, there exist many such highthroughput, solution deposition methods, such as solution shearing, doctor blading, inkjet printing, roll coating, knife blading, zone casting, etc., all of which are used to create uniform, thin films of OSCs.13,15–25 The solution shearing method forms large, oriented crystalline OSC domains, which exhibit fewer unfavorable grain boundaries and improved charge transport. This method also allows the possibility of trapping nonequilibrium molecular packing of small molecule OSCs, which in some cases may improve electronic overlap between molecules. In the case of the model OSC 6,13(bis-triisopropylsilylethynyl) pentacene (TIPS-pentacene), a packing motif with greater electronic overlap than that of the equilibrium molecular packing was demonstrated.25 Consequently, the charge a)
Address all correspondence to this author. e-mail: [email protected] b) Equal authorship. This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2014.305 J. Mater. Res., Vol. 29, No. 22, Nov 28, 2014
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transport properties of TIPS-pentacene were increased, resulting in TFTs with charge carrier mobilities above 10 cm2 V1 s1.26 In addition to the improvement of charge carrier mobilities in OSC thin films, a further area of focus is the reduction of parasitic leakage currents and crosstalk between neighboring TFTs, via the select
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