Process for High Photocurrent in IBC Solar Cells

Abstract

An interdigitated back contact solar cell fabrication process that yields cells with current‐collection efficiencies in excess of 90% in n‐type silicon is presented. This process maintains high bulk minority‐carrier lifetime through the use of diffusion gettering steps and relatively low processing temperatures. Low front and back surface recombination velocities are achieved by growing thermal oxides on these surfaces followed by a forming gas anneal. Bulk lifetimes on the order of 350μsec and front surface recombination velocities of less than 30 cm/sec are determined by comparing measured quantum efficiency data to calculated quantum efficiency using an analytical code which solves the transport equations in one dimension. These lifetimes are compared to values of 290‐190 μsec measured for cells with and without a front surface n+ layer, respectively. These were measured with a laser scanning technique using the 514 nm wavelength and are considered a lower limit to the lifetimes.