Measurement of Exciton Diffusion Lengths of Phthalocyanine Derivatives Based on Interlayer Excitation Transfer

The exciton diffusion length (L-D) of several phthalocyanines (Pcs) was investigated by use of organic photovoltaic cells, where two different p-type organic semiconductor materials, including a Pc layer, were laminated, and interlayer excitation energy transfer occurred between them. The distribution of excitons in the Pc layer that accept energy from the other p-type semiconductor material by excitation transfer should be much narrower than that of excitons created by light absorption directly. This delta-function-like generation of excitons allowed the simple analysis of exciton diffusion. The results of the analysis indicated that the planar Pcs (copper Pc and metal-free Pc) showed shorter L(D)s of around 5 nm, as compared to the 18.5 +/- 4.8 nm shown by the pyramidal-shaped Pc (tin Pc)