Impact of Non-Radiative Recombinations in Thin Film Solar Cells with Light-Trapping: an Analytical Model

Abstract

We propose an analytic electro-optical model for solar cells, and we apply it to investigate the interplay between non-radiative recombination and light trapping in crystalline silicon p-n junctions. We adopt a Lambertian scatterer as prototype for devices incorporating light trapping, and we take into account recombination both in the bulk and at interfaces by calculating analytic solutions of the transport equations. We show that solar cells with Lambertian light trapping and characteristic thickness of the order of a few tens of microns are the best choice in terms of conversion efficiency. By using our model, we quantify the optimal thickness depending on the materia l quality. Surface dynamics become a crucial factor when reducing the devices thickness and its importance is amplified in real devices where textures are used to implement light trapping, due to increased surface area. We estimate the maximum level of (effective) surface recombination which is required for thin-film cells to overcome the bulk ones, and to approach their realistic ultimate efficiency.