Photonic crystal structures for light trapping in thin-film Si solar cells: Modeling, process and optimizations

In this paper, we present our efforts on studying light trapping in thin-film silicon solar cells using photonic crystal (PC) based structures. Specifically, we propose a photonic backside texture combining periodic gratings and a distributed Bragg reflector (DBR). The mechanisms of this integrated photonic design are theoretically studied and compared with conventional PCs. We experimentally fabricate the texture using lithographic and self-assembled method on thin-film single crystalline Si (c-Si) and micro-crystalline Si (μc-Si) cells. We analyze the effects of the photonic textures on different cells and demonstrate the performance improvements. A numerical method is developed to explore the optimal multiscale textured surface and investigate light trapping limits in the wave optics regime. Using a detailed balance analysis, we show that it is possible to reach over 20% efficiency for 1.5 μm Si cells through optimal device design and fabrication.