Tantalum Nitride Hole-Blocking Layer for Efficient Silicon Solar Cells

Minimizing carrier recombination losses at contact regions by using carrier-selective contact materials, instead of heavily doping the silicon, has attracted considerable attention for high-efficiency, low-cost crystalline silicon (c-Si) solar cells. Here we present a novel and stable metal nitride based hole-blocking layer for efficient silicon solar cells. The ALD-deposited tantalum nitride (TaNx) films are demonstrated to provide excellent hole-blocking property on silicon surfaces, due to their small conduction band offset and large valence band offset with silicon. Thin TaNx films are found to provide not only moderate surface passivation to silicon surfaces, but also allow a relatively low contact resistivity at the TaNx/n-Si heterojunctions. An efficiency over 20% is achieved on n-type silicon solar cells featuring a simple full-area electron-selective TaNx contact, representing an absolute efficiency gain of 4.0% over the control device without TaNx contact.