Simulations of Optical Processes in Organic Photovoltaic Devices

108By simulation of the optical processes in photovoltaic devices it is possible to enhance both the understanding of the physical processes occurring as a result of optical absorption and also to optimize the design of devices given this understanding. Calculations allow properties that are out of reach for direct measurements, such as absorption profiles, to be evaluated. Besides, in a relatively short time on a computer, thousands of different device geometries can be simulated. This is far beyond what can be performed experimentally, both from a time and a material householding perspective, and allows optimization of device design from an optical point of view. We present a modeling approach based on a number of assumptions such as homogeneous layers, sharp and planar interfaces, scattering free optics, coherence in the stack part of the device, and incoherence when adding energies across the substrate. The model has only layer thickness, layer dielectrical functions, and exciton diffusion length as input. Many different kinds of output are possible: absorption profile, reflectance, absorbance, absorption distribution, limits for quantum efficiencies, etc. The model is applied to devices with the active material being a pure polyfluorene–copolymer or blended with C60 as the acceptor.