Excitons in organic–inorganic hybrid compounds (C nH 2 n + 1 NH 3) 2PbBr 4 ( n = 4, 5, 7 and 12)

Abstract

Thin films of microcrystalline (C n H 2 n + 1 NH 3) 2PbBr 4 ( n = 4, 5, 7 and 12) have been prepared by a modified spin-coating method, and the effect of the number of carbon atoms of the alkyl chain length ( n) on optical properties has been investigated. Absorption spectra reveal that (C n H 2 n + 1 NH 3) 2PbBr 4 films show stable excitons with a binding energy of a few hundred meV. The excitonic structure of (C n H 2 n + 1 NH 3) 2PbBr 4 varies with the number of carbon atoms. The lowest-energy exciton splits into a few fine-structure levels at low temperature. (C n H 2 n + 1 NH 3) 2PbBr 4 films ( n = 5, 7 and 12) show not only singlet excitons but also triplet excitons at low temperature, while (C 4H 9NH 3) 2PbBr 4 films show only singlet excitons. The intersystem crossing from excited singlet state to triplet state plays an important role in the relaxation process of excitons.