Efficiency Enhancement of Copper Contaminated Radial p-n Junction Solar Cells
Akram Boukai, Paul M. Haney, Aaron Katzenmeyer, Gregg M. Gallatin, Albert A. Talin, Peidong Yang
A significant fraction of the cost of a planar p-n junction silicon solar cell stems from the silicon purification process.1 Eliminating the purification step would decrease the cost, yet also decrease the solar cell efficiency significantly. Here, we have developed an alternative geometry− a radial p-n junction− different from that of a typical planar p-n junction2, 3. Radial p-n junctions have been predicted theoretically to have larger efficiencies than their planar counterparts due to a decrease in carrier collection length relative to carrier diffusion length.4 Radial p-n junctions studied here consist of micron-scale to nano-scale diameter holes etched into a copper contaminated silicon wafer using standard CMOS fabrication steps. Radial p-n junctions contaminated with copper impurities show roughly a two times increase in efficiency than similarly contaminated planar p-n junction solar cells; however the enhancement is a strong function of the radial junction pitch, with maximum enhancement occurring for a pitch that is twice the carrier diffusion length.