Maithili Ghamande
Published: 2011
Total Pages: 58
Get eBook
Organic photovoltaic devices consist of several thin layers of material with different electro-optical porperties. Since the conversion of incident photons to charge carriers occurs only in the active layers, the intensity distribution of light within the device has an important effect on the efficiency of a solar cell. The intensity in turn depends upon properties of the layers, such as refractive index, absorption coefficient, and thickness, as well as on properties of the incident light, such as angle of incidence and spectral distribution. In this work, we investigate the absorption of light in thin-film organic solar cells with computational methods. Since interference effects play an important role in thin-films, we implement a transfer matrix method to calculate the complex amplitude of the electric field at the interfaces and propagate the electromagnetic wave within layers. We apply the method to conjugated polymer/fullerene bilayer solar cells and investigate devices of two planar geometries for the relevant part of the solar spectrum and a range of angles of incidence. Our results show that the angle of incidence has a small effect on the distribution of the electric field in the active layers for a wide range of angles. For normal incidence, we confirm that the thickness of one of the layers, the layer adjacent to the metal electrode, has a large effect on the electric field distribution and find that the absorbance of light in the active layers depends strongly on the wavelength of the incident light. A reweighting of the absorbance with the solar irradiance illustrates that optimizing the design of solar cells requires a compromise between materials properties and device geometry.