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 (TaN x ) films are demonstrated to provide excellent holeblocking property on silicon surfaces, due to their small conduction band offset and large valence band offset with silicon. Thin TaN x films are found to provide not only moderate surface passivation to silicon surfaces, but also allow a relatively low contact resistivity at the TaN x n-Si heterojunctions. An efficiency over 20% is achieved on n-type silicon solar cells featuring a simple full-area electron-selective TaN x contact, representing an absolute efficiency gain of 4.0% over the control device without TaN x contact.