Measurement of nanoscale external quantum efficiency of conjugated polymer: Fullerene solar cells by photoconductive atomic force microscopy

Abstract

Photoconductive atomic force microscopy is used to investigate nanoscale incident photon-to-current efficiency spectra of polymer bulk heterojunction solar cells based on poly[2-methoxy-5-(3,7-dimethyloctyloxy)]-1,4- phenylenevinylene (MDMO-PPV) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71 BM). Nanoscale external quantum efficiency reveals the complex morphology of MDMO-PPV: PC71 BM films cast from toluene solution. Not only electron transfer from the photoexcited donor to the fullerene but also hole transfer process from photoexcited fullerene to the donor phase due to highest occupied molecular orbital offset is observed. The difference in performance between toluene and chlorobenzene-cast devices is explained by the variation in relative contributions from two charge transfer mechanisms. © 2010 American Institute of Physics.