Silicon surface passivation with atomic layer deposited aluminum nitride

We propose a new surface passivation material for crystalline silicon solar cells, namely atomic layer deposited aluminium nitride (ALD AlN). AlN has multiple benefits as compared to more commonly used Al2O3, i.e. it has better optical properties, higher hydrogen concentration and better suitability for phosphorous emitter passivation due to lower fixed charge. In addition to introducing a new ALD passivation material, we study here various deposition temperatures and postdeposition heat treatments. The best surface passivation quality is reached with high deposition temperatures followed by a combination of longer low temperature anneal and a short high temperature firing. With the optimized parameters, extremely low interface defect density values of ~4·1011 eV-1cm-2 are reached demonstrating the potential of ALD AlN as future surface passivation material.