Photonic light trapping and electrical transport in thin-film silicon solar cells

Abstract

Efficient solar cells require both strong absorption and effective collection of photogenerated carriers. With these requirements in mind, the absorber layer should be optically thick but electrically thin, to benefit from reduced bulk transport losses. It is therefore important to clarify whether thin-film silicon solar cells can compete with conventional wafer-based devices. In this paper we present a theoretical study of optical and electro-optical performance of thin-film crystalline silicon (c-Si) solar cells implementing light-trapping schemes. First, we use Rigorous Coupled-Wave Analysis (RCWA) to assess the light-trapping capabilities of a number of photonic structures characterized by different levels of disorder. Then, we present two approaches for electro-optical modeling of textured solar cells: a simplified analytic model and a numerical approach that combines RCWA and the Finite-Element Method. We consider both bulk and surface recombination in solar cells with the absorber thickness ranging from 1 to 100μm. Our results predict that with state-of-the-art material quality of thin c-Si layers, the optimal absorber thickness is of the order of tens of microns. Furthermore, we show that thin-film solar cells with realistic material parameters can outperform bulk ones, provided surface recombination is below a critical value, which is compatible with present-day surface passivation technologies. This gives prospects for high-efficiency solar cells with much smaller c-Si thickness than in present wafer-based ones.