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Title: Surface-directed spinodal decomposition in poly[3-hexylthiophene] and C61-butyric acid methyl ester blends
Authors: Vaynzof, Y.
Kabra, D.
Zhao, L.
Chua, L.L. 
Steiner, U.
Friend, R.H. 
Keywords: Bulk heterojunction photovoltaic cells
C61-butyric acid methyl ester (PCBM)
Photoemission spectroscopy
Spinodal phase separation
Issue Date: 25-Jan-2011
Citation: Vaynzof, Y., Kabra, D., Zhao, L., Chua, L.L., Steiner, U., Friend, R.H. (2011-01-25). Surface-directed spinodal decomposition in poly[3-hexylthiophene] and C61-butyric acid methyl ester blends. ACS Nano 5 (1) : 329-336. ScholarBank@NUS Repository.
Abstract: Demixed blends of poly[3-hexylthiophene] (P3HT) and C61-butyric acid methyl ester (PCBM) are widely used in photovoltaic diodes (PV) and show excellent quantum efficiency and charge collection properties. We find the empirically optimized literature process conditions give rise to demixing during solvent (chlorobenzene) evaporation by spinodal decomposition. Ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) results are consistent with the formation of 1-2 nmthick surface layers on both interfaces, which trigger the formation of surface-directed waves emanating from both film surfaces. This observation is evidence that spinodal demixing (leading to a bicontinuous phase morphology) precedes the crystallization of the two components. We propose a model for the interplay of demixing and crystallization which explains the broadly similar PV performance for devices made with the bottom electrodes either as hole or electron collector. The process regime of temporal separation of demixing and crystallization is attractive because it provides a way to control the morphology and thereby the efficiency of PV devices. © 2011 American Chemical Society.
Source Title: ACS Nano
ISSN: 19360851
DOI: 10.1021/nn102899g
Appears in Collections:Staff Publications

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