Measuring the exciton diffusion length of C60 in organic planar heterojunction solar cells

Planar copper phthalocyanine (CuPc)/C-60 heterojunction solar cells with a 2 nm layer of bathocuproine (BCP) inserted into the C-60 layer were fabricated and characterized. The 2 nm BCP layer in the devices was used as an electronically selective sieve allowing the electron current through but blocking the excitons in the C-60 layer. By combining the experimental results with the optical modeling, the effective triplet exciton diffusion length in C-60 was confirmed to be 30-35 nm under the device working condition. We demonstrate a simple, useful method to determine the exciton diffusion lengths of organic electron acceptors. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim