We propose to study the kinetics and thermodynamics of polymer:fullerene composite association to provide insight into engineering increased efficiency organic photovoltaics. The structure of P:NP thin films can be designed by controlling P:NP miscibility, as well as non-equilibrium effects from solution and thermal processing. We demonstrated that, varying polymer Mw and P:NP stoichiometry, a variety of lateral morphologies can be obtained, ranging from uniformity to spinodal-like connectivity. Reflectometry is required to complement ongoing work in dynamic & static light scattering and AFM. Specifically, we seek to examine: (a) the composition stratification orthogonal to the film and (b) the mechanism of topographical surface excitation.