Optimization of the back contact geometry for high efficiency solar cells

Minority carrier lifetime measurements are reported for float zone silicon wafers with well passivated surfaces and different periodic metallization patterns at one surface. The authors use the microwave reflection recovery technique to monitor the photoconductance decay after a short light pulse. The results demonstrate the sensitive dependence of the decay time not only on the fractional area ratio of the metallized regions but also on the distance between the contacts at constant metal to oxide ratio. The authors explain their experimental results by applying a novel three-dimensional simulation technique which is based on the solution of the electronic transport equations in Fourier space. The results of experiments and theory are used to determine the optimum metallization pattern, i.e. the optimum area of the contact and the optimum spacing, for the back surface of high efficiency solar cells