Insights on the morphology of polymer donor:acceptor blends by optical metrology

One of the main challenges that need to be addressed to successfully implement polymer donor:acceptor blends as photoactive layers in Organic Electronic (OE) devices (e.g. Organic Photovoltaics - OPV) is the understanding of the effect of the processing and printing parameters on their morphology and the distribution of the donor and acceptor components in the photoactive layer. In this work, we present a comprehensive optical metrology methodology for the determination of the morphology of well-established polymer blends that include poly(3-hexylthiophene (P3HT) donors and phenyl-C61-butyric acid methyl ester (PC60BM) and phenyl-C71-butyric acid methyl ester (PC71BM) acceptors, which are used as photoactive layers for OPVs. Also, we determine the distribution of the donor and acceptor phases in the blend by analysis of the measured pseudodielectric function 〈ε(ω)〉 by the use of effective medium theory modelling in combination with an exponential gradient model that approximates the modification of the refractive index in the different parts of the blend. This methodology emphasizes the capabilities and potential of optical metrology to be used as a quality control tool in large scale manufacturing for OE devices.