Hole transport of trans‐1,2‐biscarbazolylcyclobutane‐doped poly(bisphenol A carbonate) film

The hole transport of trans ‐1,2‐biscarbazolylcyclobutane (CB) doped poly(bisphenol A carbonate) (PC) film has been investigated in the CB concentration range of 3.8 × 10 −4 mol cm −3 (12 wt%) to 1.6 × 10 −3 mol cm −3 (51 wt%). The hole mobility increased drastically with increasing CB concentration. The hole mobility was analyzed by a random hopping model. The localization radius ρ 0 of the CB/PC system was 1.9 Å, which is larger than that obtained for the N ‐isopropyl‐carbazole‐doped PC system. This suggests that the larger localization radius of the CB/PC system is related to the larger spatial extent of the CB molecule. The highest hole mobility of 2.9 × 10 −6 cm 2 V −1 s −1 was obtained when the CB concentration was 1.6 × 10 −3 mol cm −3 (51 wt%) at E = 1.6 × 10 5 V cm −1 and T = 298 K. This mobility is about 10 times higher than that of poly( N ‐vinylcarbazole) (PVCz). The activation energy of hole mobility for the CB/PC system decreased with increasing CB concentration and was 0.31 eV at 51 wt% of CB, which is lower than the 0.45 eV for PVCz. The low activation energy for the CB/PC system is ascribed to the absence of an excimer‐forming site that works as a multiple‐trapping site for hole carriers.