Crystallization of solution processable amorphous tetrabenzoporphyrin films

The dynamic process of crystallization of nickel-tetrabenzoporphyrin (NTBP) from its amorphous precursor film was investigated. NTBP crystalline films with a preferential orientation were obtained through the recrystalization from its precursor film deposited on polyimide (PI) substrate. This preferential orientation, with (001) plane lies in the film plane, increases the in-plane electrical conductivity of the film dramatically in comparison with that deposited on a glass substrate where no preferential orientation was observed. Such a preferential orientation of NTBP is caused by the local order of the PI surface molecules which act as favorable nucleation sites to grow NTBP in preferential crystallographic direction. This view is supported by the observed lower activation energy (0.96 eV) required for continuing crystallization on PI than that on glass (1.27 eV). The time dependence of the nucleus density of NTBP follows N ~ tn, where n = 1 and 1.5 for PI and glass substrates, respectively. This can be interpreted as a result of lacking of nucleation centers on the glass substrate hence newly activated sites are required to continue the crystallization, while on the PI substrate such process is not required.