Electric conduction of PbBr-based layered perovskite organic-inorganic superlattice having carbazole chromophore-linked ammonium molecule as an organic layer

摘要

We have successfully prepared thin films of PbBr-based layered perovskite having hole-transporting carbazole chromophore-linked ammonium molecules as an organic layer by a simple spin-coating from the N,N-dimethylformamide solution in which the stoichiom-etric amount of lead bromide and carbazole-linked ammonium bromides was dissolved. Their X-ray diffraction profiles exhibited that their layer structure formed (0 0 n)-orienta-tion, where c-axis is perpendicular to the substrate plane. Their layer structure depended on the alkyl chain length of ammonium molecules. When methylene length of C_5H_10 was employed in the carbazole-linked ammonium molecules, highest orderliness of the layer structure was attained; higher-order X-ray diffraction peaks were observed in the layered perovskite films. In the layered pervskite film, in-plane conduction, namely conduction in the direction of the stacking of carbazole chromophore, was measured. For comparison, conductivity of poly(N-vinylcarbazole) (PVCBz) thin film was also measured. The conductivity of the layered perovskite thin film (1.8 × l0~(-10)Scm~(-1) at 303 K) was about three order of magnitude larger than that of the PVCBz thin film (5.3 × l0~(-14)Scm~(-1) at 303 K). Despite the much higher conductivity of the layered peroskite thin film, the activation energy of the conductivity of the layered perovskite thin film (1.44 eV) was about 2.4 times larger than that of the PVCBz thin film (0.61 eV). This phenomenon is probably due to difference in film morphology through considering the results of AFM observation.