Temperature Dependence of the Drift Mobility of Poly(9,9′-dioctylfluorene-co-benzothiadiazole)-Based Thin-Film Devices

Abstract

Charge transport in spin coated thin films of poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT) was studied using the Photo-Current Extraction by the Linear Increasing Voltage (Photo-CELIV) method in the temperature range of 120 to 420 K. A continuous change in the slope of a lnμ versus T–2 plot was detected at 205 K with a very weak temperature dependence of the mobility at lower temperatures. According to the Gaussian Disorder Model (GDM), this behavior can be attributed to a progressive decrease in the dispersiveness of the charge transport. In this sense, the weak temperature dependence of the mobility at low temperatures arises from the nonequilibrium condition between thermal released and trapped charges, so the transport becomes trap controlled at low temperature. Furthermore, another change in the mobility behavior was observed at about 360 K, which was related to the glass transitions of the material. This indicates that even for thin films the drift mobility can be significantly affected by ...