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 (TaNx) 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 TaNx 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 TaNx 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.