Effect of concentration of DH6T on the performance of photoconductor fabricated using blends of P3HT and DH6T

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 potential 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 estimated 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 morphology 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 photoresponse 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).