Modification of PCBM Crystallization via Incorporation of C60 in Polymer/Fullerene Solar Cells

Abstract

The morphological effects of the incorporation of C60 into blended thin-films of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) are investigated. The results show that addition of C60 readily alters the growth-rate and morphology of PCBM crystallites under different environmental conditions. The effect of C60 on the growth of large PCBM crystallites is thoroughly characterized using optical microscopy, electron microscopy and UV-visible absorption spectroscopy. Results show that C60 incorporation modifies fullerene aggregation and crystallization and greatly reduces the average crystallite size at C60 loadings of approximate to 50 wt% in the fullerene phase. Organic field-effect transistors (OFETs) are prepared to evaluate the electron mobility of PCBM/C60 films and organic solar cells (OSCs) are fabricated from mixed-fullerene active layers to evaluate their performance. It is demonstrated that the use of fullerene mixtures in organic electronic applications is a viable approach to produce more stable devices and to control the growth of micrometer-sized fullerene crystals.