Solution-grown small-molecule organic semiconductor with enhanced crystal alignment and areal coverage for organic thin film transistors

Sheng Bi,Zhengran He,Jihua Chen,Dawen Li

doi:10.1063/1.4927577

Sheng Bi, Zhengran He + Show 2 more

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https://doi.org/10.1063/1.4927577

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Abstract

Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5″-n-hexyl-2,2′,5′,2″]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10−2 cm2/V s, which is the highest mobility from SMDPPEH ever reported.

Highlights

Solution processable small-molecule organic semiconductors have been intensively studied nowadays due to their relatively high charge carrier transport,[1,2,3,4] and cost-effectiveness in fabrication, which make them promising for applications in flexible electronics over large areas.[5,6,7] thin films drop casted from small-molecule organic semiconductors typically exhibit random crystal orientation with poor coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs).[8,9] it is mandatory to well align the crystals in order to achieve performance consistency of OTFTs
When SMDPPEH is drop casted from single chloroform solvent, a few scattered crystals are formed on the substrate with random orientation and poor areal coverage (Figure 1(b)), while drop casted from chloroform/ethanol double solvents, the resultant films exhibit enhanced crystal density as shown in the optical images of Figure 1(c), because the “bad” solvent ethanol increases nucleation seeds for SMDPPEH crystallization
In both cases of crystal growth in single and double solvents, there is no uniform crystal orientation, which could cause significant device performance variation if such films are used as the active layer of OTFTs.[33,34]

Summary

INTRODUCTION

When drop casted from single solvent (chloroform), SMDPPEH formed crystals with significant misorientation and poor film coverage. The application of CESA method combined with double solvent system leads to greatly enhanced crystal alignment, film coverage and crystal width. The SMDPPEH OTFTs based on CESA approach and double solvent system exhibit a mobility of up to 1.6 × 10−2 cm2/Vs. To the best of our knowledge, this is the highest mobility from SMDPPEH ever reported

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSIONS