Organic photovoltaics utilize a combination of donor-acceptor polymer:fullerene blend for its best performance. Spin-casted interpenetrating nanosized donor-acceptor domains contribute to efficient charge generation in bulk heterojunction (BHJ) solar cells.1 However, the blend nano-morphology and ultimately the device efficiency is critically dependent on the choice of precursor organic solvent used for film casting.2,3,4 In order to get an insight into the role of solvent in dictating film morphology, the chemical nature of polymer:PCBM interactions in solution has to be unravelled. Using broadband femtosecond transient absorption spectroscopy on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM) mixtures, we show that charge transfer rates in solutions are as fast as ~130 fs, similar to that observed in spin-casted films.5The ultrafast rise of the characteristic CT band at ~700 nm along with the formation of polaron absorption features at ~900 nm and ~1050 nm, indicate the presence of photogenerated charges. The spectroscopic characterization and modelling of the polymer:PCBM solution structures would be discussed in detail. Our observation of efficient CT state generation in solution indicates existence of strongly coupled donor-acceptor structures, and thereby opens up possible avenues for chemically pre-forming stable donor-acceptor interfaces via an inherent solvent control.References [1] G. Dennler, M. C. Scharber, and C. J. Brabec, Adv. Mat., 2009 , 21, 1323.[2] S. Kouijzer et al. J. Am. Chem. Soc., 2013 , 135, 12057�12067.[3] X-T. Hao, L. J. McKimmie, and T. A. Smith, J. Phys. Chem. Lett., 2011 , 2, 1520.[4] M. T. Dang et al., Solar Energy Mat. Solar Cells, 2011,  95, 3408.[5] I. Hwang, D. Moses, and A. J. Heeger, J. Phys. Chem. C, 2008  , 112, 4350.

Capturing photoinduced charge transfer states of polymer:PCBM mixtures in solution

248th National Meeting (2014)

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