Photogeneration in Doped and Blended Conjugated Polymers

On the other hand, this raises a fundamental question as to why the initially generated e-h pair escapes from its mutual coulombic potential so easily while in a single component system coulombic effects cut down the yield to below 10 .  

In order to answer this question, Mihailetchi et al. [39] measured photogeneration in a blend of poly(2-methoxy-5-(3, 7 -dimethyloctyloxy)-phenylene vinylene (OCICIO-PPV) and PCBM as function of applied voltage and temperature. Presuming that the essential intermediate is an optically generated coulombically bound e-h pair located at an internal donor-acceptor hetero-junction that can either dissociate completely or recombine geminately, they analyzed their data in terms of Braun s model [22]. Based upon a broad distribution of e-h pair distances centered at 1.3 nm and invoking a value of 1 [is for the e-h pair lifetime they were able to rationalize their experimental results that include a measured 60% carrier yield at a built-in field of 7.5 X 10 Vcm at room temperature. However, an open question appears to be their choice of a pair lifetime of 1 [is. Recent experiments on a blend of a polyfiuo-renecopolymer and PCBM reveal a broad distribution of lifetimes albeit centered at a value as short as 1 ns [40]. 

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