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.