Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Effect of concentration of DH6T on the performance of photoconductor fabricated using blends of P3HT and DH6T Shalu Chaudhary a , Kshitij Bhargava b , Nidhi Yadav a , Mukesh P. Joshi c , Vipul Singh a,* a Molecular and Nanoelectronics Research Group (MNRG), Discipline of Electrical Engineering, IIT Indore, Indore, Madhya Pradesh, 453-552, India b Department of Electrical Engineering, Institute of Infrastructure Technology Research and Management, Ahmedabad, Gujarat, 380026, India c Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore, 452013, India ARTICLE INFO Keywords: Small molecule Conjugated polymer Barrier potential Photoconductor ABSTRACT The influence of small molecule (SM) α, ω-di-hexyl-sexithiophene (DH6T) concentration, in the blends of conjugated polymer (CP) poly (3-hexylthiophene) (P3HT) and DH6T, was investigated in terms of barrier po- tential reduction and improved photoresponse of the fabricated photoconductor using these blends. Barrier potential in Au/P3HT:DH6T/Au device structure, occurring at the interface of Au (top)/P3HT:DH6Twas esti- mated by Fowler Nordheim (FN) tunneling model-based analysis of I-V characteristics. The barrier potential of the fabricated device was observed to decrease upon addition of a small quantity of DH6T in comparison to the pristine polymer-based device. This reduction in barrier was attributed to the improved ordering and mor- phology of the polymer chains upon blending it with an SM. The variation in the ordering of the polymer chains was further confirmed with Photoluminescence spectroscopy, Absorption spectroscopy, and XRD data. Subsequently, it was also observed that only up to a definite SM concentration (25% in this study) ordering of polymer chains improved causing a reduction in barrier potential and subsequent improvement in the photo- response of the fabricated devices. Finally, it was observed that the optimized blending of CP and SM could to be useful in reducing the effect of penetration of Au inside the CP matrix in the top contact configuration thereby resulting in the reduction of a barrier for carrier injection which is generally lower in the bottom contact configurations. These studies are critical from the point of view of the development of photoconductors and photosensitive top contact organic field effect transistors (OFETs). 1. Introduction In the last few decades, organic electronic devices have drawn a great consideration owing to their simple, low cost, flexible, large area fabrication and processing techniques [1–5]. In recent past, immense efforts have been devoted in the field of research and development of various organic devices such as OFETs, organic photovoltaics (OPVs), OLEDs, organic photodetectors (OPDs) etc. [1,2,6–10]. Moreover, im- provement in the performance of existing devices has opened new paradigms in sensor and bioelectronic applications [1]. Organic semi- conductors are broadly divided in two categories; CP based and SM- based organic semiconductors. CPs can be processed via solution pro- cessed techniques; hence the fabrication of cost-effective solution-pro- cessed efficient electronic devices [1–5]. SM based organic semi- conductors generally have an inferior solubility in several organic solvents hence vacuum thermal evaporation technique is generally used to fabricate the device with these small molecules [2,3and6]. On the other hand, thermal evaporation process has limitations in terms of high cost and limited coverage area of fabricated devices. These lim- itations further restrict their applications in the multidisciplinary fields [2,6]. Devices fabricated using SM retain enhanced optoelectronic properties while comparing to the CP based devices because thin films of SMs are more uniform and well-ordered [6,11]. So both CP and SM have several advantage and limitations over each other; hence to in- corporate the advantages of both, by means of mixing or blending of two moieties can be adopted. The blends of different materials can be prepared with the aim of combining the valuable optical properties of each constituting materials [14–18]. Blending is useful to enhance the electronic and optoelectronic characteristics of the fabricated devices than those achieved solely by materials when incorporated individually [5,7,16–21]. Blending of two different materials requires that each of the material should be soluble in a common solvent for a consequent deposition into the thin films, consisting of each participating materials [15–21]. Blending of SMs with CPs is helpful to improve the solution https://doi.org/10.1016/j.optmat.2019.01.017 Received 23 October 2018; Received in revised form 4 December 2018; Accepted 2 January 2019 * Corresponding author. E-mail addresses: vipul.iiti@gmail.com, vipul@iiti.ac.in (V. Singh). Optical Materials 89 (2019) 214–223 0925-3467/ © 2019 Elsevier B.V. All rights reserved. T