Tantalum Nitride Electron-Selective Contact for Crystalline Silicon Solar Cells

Minimizing carrier recombination 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. A novel electron-selective, passivating contact for c-Si solar cells is presented. Tantalum nitride (TaN _x) thin films deposited by atomic layer deposition are demonstrated to provide excellent electron-transporting and hole-blocking properties to the silicon surface, due to their small conduction band offset and large valence band offset. Thin TaN_x interlayers provide moderate passivation of the silicon surfaces while simultaneously allowing a low contact resistivity to n-type silicon. A power conversion efficiency (PCE) of over 20% is demonstrated with c-Si solar cells featuring a simple full-area electron-selective TaN_x contact, which significantly improves the fill factor and the open circuit voltage (V_oc) and hence provides the higher PCE. The work opens up the possibility of using metal nitrides, instead of metal oxides, as carrier-selective contacts or electron transport layers for photovoltaic devices.