The mechanism of free charge carrier generation via dissociation of photogenerated excitons in polymer:fullerene photovoltaic blends is still poorly understood, despite intensive research efforts by many groups. In particular, the role played by interfacial charge-transfer (CT) states in the generation of free charges remains largely unclear. It is often assumed that these CT-states are intermediates in the formation of free charge carriers and are themselves prone to a field-dependent splitting process in working devices. However, largely inconsistent experimental results have been presented to date, even for the same material systems. Gaining more insight into the role CT-states play is not only of fundamental interest, but also necessary to better understand the bias dependence of the photocurrent, in particular the origin of the fill factor, which largely determines the device efficiency.
© 2012 Optical Society of AmericaPDF Article
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