The highest efficiency (24.7%) crystalline silicon solar cell produced to date is the PERL (Passivated Emitter Rear Locally diffused) cell first developed by Martin Green et al. See IEEE Transactions on Electron Devices Vol. 46, No. 10, October 1999. However, these cells are costly to fabricate since expensive float zone silicon was utilized for the device fabrication and the use of photolithography for metal contact formation is not conducive to low manufacturing cost. There is a need for lower cost solar cells with comparable efficiency to the PERL cell, and improved methods of fabricating these cells that does not involve the high temperature diffusion of boron for the formation of back contacts.
As silicon wafer thickness is reduced to reduce silicon consumption and hence manufacturing costs of photovoltaic products, more of the long wavelength infrared radiation will pass through the thin wafer without being absorbed, due to the relatively poor absorption coefficient of silicon. Consequently cell efficiency is reduced for thin (less than roughly 50 microns) silicon cells. There is a need for solar cell structures which can compensate for the poor absorption of longer wavelength light.