PCBM:P3HT miscibility and interfacial structure as determined by neutron scattering

A mixture of poly(3-hexyl thiophene) (P3HT) and 1-(3-methyloxycarbonyl) propy(1-phenyl [6,6]) C₆₁ (PCBM) is a common, and fairly promising, conjugated polymer:fullerene mixture that is used as an active layer in bulk heterojunction organic photovoltaics. Unfortunately, the precise morphology, interfacial structure, and composition of phases that exist in this phase separated bulk heterojunction material is difficult to ascertain. In this study, we have taken advantage of the fact that neutron scattering and reflectivity offers a unique opportunity to monitor the structure, interfaces, morphology, and composition of polymer:fullerene systems that dominate bulk heterojunctions. This is because the neutron scattering length density (SLD) of a protonated matrix differs significantly from that of the fullerene as the SLD of fullerenes are similar to that of deuterated organic compounds. In this study, small angle neutron scattering and neutron reflectivity results show that a mixture of P3HT and PCBM is significantly more miscible than previously thought. In this talk we will discuss how this information will have a dramatic impact on the development of methods to design an optimal organic photovoltaic bulk heterojunction.