Disordered Photonic Crystal Slabs for Thin-Film Photovoltaics

Photonic crystal nanostructures are the foundation for many optical applications such as nanochip waveguides, optical fibres, and high-Q nanocavities. Recently, researchers have begun to explore the use of photonic crystal slabs to increase the overall absorption of sunlight in thin-film solar photovoltaic (PV) cells. Currently, amorphous silicon (a-Si:H) thin-film technologies can only achieve efficiencies of up to 16% in laboratories and less than 10% in manufactured commercial products. The difficulty in improving these efficiencies arises from the inherent band gap properties of the crystalline silicon layer: the natural photonic bandgap in the near infrared (IR) region of light prohibits almost a third of the entire available solar spectrum from being absorbed. Some of this loss can be salvaged by increasing the thickness of the silicon layer, but this drives the price of the cell up and has very limited potential. However, using photonic crystal nanostructures in the active layer of the cell can decrease the reflection of light at the surface and increase the photon path within the film, enhancing the collection and conversion efficiencies over a broad spectrum. The absorption can be further increased by introducing pseudo-disorder within the structures. The purpose of this study was to explore the physical parameters of this disorder and quantitatively optimize absorption.