Efficient bilayer heterojunction polymer solar cells with bumpy donor-acceptor interface formed by facile polymer blend

We demonstrated a facile method for the fabrication of bilayer polymer solar cells with a controlled heterojunction structure via simple polymer blends. The spontaneous phase separation of poly(3-hexylthiophene)/polyethylene glycol blends provides a bumpy electron-donor layer with characteristic circular depressions. The diameter and depth of the circular depressions can be controlled by varying the PEG content of the blend. The deposition of [6,6]-phenyl-C61-butyric acid methyl ester as an electron-acceptor layer then creates an interpenetrating donor-acceptor interface for bilayer heterojunction polymer solar cells. The bumpy morphology of the interface results in a significant enhancement in the power conversion efficiency over that of the bilayer polymer solar cells with a typical planar interface, which is mainly due to an increase of photocurrent. An estimation of the field-dependent possibility of charge separation indicates that charge extraction is more efficient than charge recombination in the bilayer devices and the increase in the interfacial area of solar cells with a bumpy-interface leads to generate more electron-hole pairs at the interface. (C) 2012 Elsevier B.V. All rights reserved.This study was supported by the Korea Institute of Science and Technology (KIST) Future Resource Research Program. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology ( 2011-0025491 )