Phase separation induced high mobility and electrical stability in organic field-effect transistors Deepak Bharti, Shree Prakash Tiwari* Department of Electrical Engineering, Indian Institute of Technology Jodhpur, Jodhpur, Rajasthan 342011, India A R T I C L E I N F O Article history: Received 11 July 2016 Received in revised form 19 August 2016 Accepted 5 September 2016 Available online xxx Keywords: Organic field-effect transistors Phase separation High mobility Electrical stability Bias-stress A B S T R A C T Phase separation induced high carrier mobility and electrical stability are achieved in organic field-effect transistors using TIPS-pentacene:polystyrene blends. Rigid Si/SiO 2 substrate was especially chosen to explore the phase separation. A vertical phase separation between TIPS-pentacene and polystyrene as confirmed from scanning electron microscopic image, evetually leads to excellent carrier mobility in polymer blend devices compared to that of neat TIPS-pentacene. Maximum hole mobility improved from 0.2 cm 2 V 1 s 1 for neat TIPS-pentacene on SiO 2 to 2.6 cm 2 V 1 s 1 for TIPS-pentacene blends with PS, with average value of 1.5 cm 2 V 1 s 1 . Apart from higher mobility, TIPS-pentacene:PS blend devices also showed much lower decay in drain current (30%) during a constant bias-stress of 2 h, compared to neat devices (80%). Interestingly, This decay was fully recovered for blend devices under rest conditions. The corresponding shift in the threshold voltage due to bias-stress was lower for TIPS-pentacene:PS device due to better quality of interface as confirmed by lower values of density of interface traps and higher trapping time. High electrical stability in TIPS-pentacene:polystyrene blend devices was also supported by repeatabiliiy studies, which exhibited nearly unchanged device characteristics. ã 2016 Elsevier B.V. All rights reserved. 1. Introduction High carrier mobility and electrical stability are highly desirable features for organic field-effect transistors (OFETs), which are the key devices for various applications such as drivers for flat panel displays, radio frequency identification (RFID) tags, sensors, and complementary circuits [1–4]. Solution processing of the active material in OFET device, i.e. the organic semiconductor is highly sought after for its attractive advantages of low cost and simplicity. However, ameliorating the quality of dielectric-semiconductor interface in solution processed OFETs is quite challenging due to numerous intricate reasons related with material properties of dielectric and semiconductor and processing conditions involved. Use of a polymeric gate dielectric has been demonstrated as one of the simple ways to form a high quality semiconductor-dielectric interface leading to remarkable performance [5,6]. A suitable polymeric dielectric material also conceals the defects of the inorganic dielectric and acts as a barrier for the moisture to reaching inorganic dielectric surface [7], leading to superior electrical performance and electrical stability in OFETs [8]. The advantages of a polymeric dielectric can further be boosted if the dielectric-semiconductor interface is developed uniformly from organic semiconductor and polymer blends with proper phase separation [9,10], which mostly occurs for small molecule organic semiconductors. A surface energy driven vertical phase separation accounts for a high quality interface in semiconductor and polymer blend films [11], paving the way for improved performance and stability in OFETs [9,12,13]. Various polymeric materials including poly(triarylamine) (PTAA), poly(methylmethacrylate) (PMMA), poly(a-methylstyr- ene) (P-aMS), and polystyrene (PS) have been explored with small molecule semiconductors like 2,8-Difluoro-5,11-bis(triethylsilyle- thynyl)anthradithiophene (DiF-TES-ADT), 6,13-Bis(triisopropylsi- lylethynyl)pentacene (TIPS-pentacene), and 2,7-Dioctyl[1] benzothieno[3,2-b][1]benzothiophene (C8-BTBT) to demonstrate high mobility in OFETs [9,11,13–18]. TIPS-pentacene is one of the most researched solution processed organic semiconductor due to merits of its intrinsic high mobility and air stability [19–25], with maximum reported mobility value approaching to 11.0 cm 2 V 1 s 1 [20]. However, number of reports demonstrating values higher than 1.0 cm 2 V 1 s 1 is still very few. Moreover, reports on high mobility blend OFETs with TIPS-pentacene are rare with maximum reported mobility of 2.8 cm 2 V 1 s 1 [17]. In addition, the method used to deposit films from the organic semiconductor and polymer blend solutions is widely spin coating [5,14,17], however, it does * Corresponding author. E-mail address: sptiwari@iitj.ac.in (S.P. Tiwari). http://dx.doi.org/10.1016/j.synthmet.2016.09.002 0379-6779/ã 2016 Elsevier B.V. All rights reserved. Synthetic Metals xxx (2016) xxx–xxx G Model SYNMET 15439 No. of Pages 6 Please cite this article in press as: D. Bharti, S.P. Tiwari, Phase separation induced high mobility and electrical stability in organic field-effect transistors, Synthetic Met. (2016), http://dx.doi.org/10.1016/j.synthmet.2016.09.002 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/sy nmet