High-efficiency emitter-wrap-through cells

In order to further decrease cost of solar electricity cheaper silicon wafers with low bulk diffusion length have to be used. These wafers are a challenge for adapted cell concepts since the diffusion length can even fall short of the cell thickness and therefore strongly reduce the short-circuit current in standard cells. The emitter-wrap-through (EWT) concept is very suitable for material with a diffusion length below the cell thickness as will be demonstrated in this paper. In contrast to the rear-contacted cell (RCC) that will also be treated in this article, the front emitter is contacted through via-holes and contributes very efficiently to the overall current collection. By this mechanism, the EWT performance becomes nearly independent of the bulk diffusion length as will be demonstrated by fabricated EWT and RCC on degrading Czochralski material. Measuring the respective cells on the same wafer at different degradation states is a very elegant way to get informations about the cell performances for different diffusion lengths. These measurements match exactly the predictions from our 2D simulations.