Buffer layer formation in organic photovoltaic cells by self-organization of poly(dimethylsiloxane)s

A surface-segregated thin layer of poly(dimethylsiloxane)-block-poly(methylmethacrylate) (PDMS-b-PMMA) formed by self-organization during spin-coating was utilized as an interfacial buffer layer in organic photovoltaic cells. X-ray photoelectron spectroscopy revealed that PDMS-b-PMMA mixed into the coating solution spontaneously accumulated at the surface of the active layer due to the low surface energy of PDMS. The introduction of the PDMS-b-PMMA layer in bulk-heterojunction cells of poly(3-hexylthiophene):[6,6]-phenyl C-61-butyric acid methyl ester resulted in an improvement of the power conversion efficiency (PCE) of the cells from 3.05% to 3.56% on average. The highest PCE of 3.86% was achieved with 0.4 mg ml(-1) of PDMS-b-PMMA. These results indicate that the PDMS-b-PMMA layer formed by self-organization provides a facile and versatile approach to improve the photovoltaic performance, possibly by suppressing charge carrier recombination at the organic/metal interface. (C) 2009 Elsevier B.V. All rights reserved.