This paper presents a quantitative analysis of perimeter losses in higheficiency silicon solar cells. A new method of numerical modelling is used, which provides the means to simulate a full-sized solar cell, including its perimeter region. We analyse the reduction in eficiency due to perimeter losses as a function of the distance between the active cell area and the cut edge. It is shown how the optimum distance depends on whether the cells in the panel are shingled or not. The simulations also indicate that passivating the cut-face with a thermal oxide does not increase cell eficiency substantially. Therefore, doping schemes for the perimeter domain are suggested in order to increase eficiency levels above present standards. Finally, perimeter effects in cells that remain embedded in the wafer during the eficiency measurement are outlined.
PURPOSE OF THIS WORK
he silicon cells with the highest efficiency, fabricated a t the University of New South Wales, remain embedded in the wafer when the efficiency is measured (on an aperture area basis), because cutting T the cells out of the wafer would create a large number of recombination centres at the cut-face.
When the cells are aligned in panels, however, the perimeter domain must be removed, otherwise the totalarea-based efficiency of the panel would suffer. How much is the efficiency degraded by perimeter losses in such applications? How must the perimeter region be designed in order to obtain optimum cell performance? How much do perimeter losses decline relative to total losses when the cell is made larger?
In order to answer these questions in a general way, we simulated numerically a full-sized solar cell with various perimeter structures.