Improved Auger recombination models: Consequences for c-Si solar cells

Abstract

Recently, the parameterisation of Auger recombination in c-Si has been revised by two separate studies, both of which reached very similar conclusions. A key change is that the ratio of the Auger coefficients for n- and p-type Si (Cn/Cp) has been found to be significantly lower than previously accepted. In this work, we explore the implications of these findings for c-Si solar cells. In particular, we seek to answer the question of whether any intrinsic advantage is expected for n-type vs p-type doping for c-Si solar cells in general, or for particular device architectures. We focus on simple analytical parameters and models in order to elucidate the relevant physical mechanisms, making use of more complex numerical modelling to complement these and validate our conclusions. A key conclusion is that the new models predict improved intrinsic performance potential for n-type devices, with p-type Si retaining an intrinsic advantage only when surface recombination and transport losses are very close to zero. n-type quickly becomes more efficient when non-zero surface recombination is introduced, and widens its advantage with increasing surface saturation current density J0. In particular, n-type back-junction devices show higher efficiency potential and less sensitivity to bulk resistivity variation than p-type equivalents, thanks to lower lateral transport losses for majority carriers in the Si bulk. Meanwhile, an analysis of the intrinsic performance potential of highly doped n- and p-type Si reveals no significant intrinsic advantage for either type as transport layers.