Boron doped nanocrystalline silicon: understanding a tricky material for high performance heterojunction solar cells

The best silicon heterojunction (SHJ) solar cells show the potential of nanocrystalline silicon (nc-Si:H) to improve their performance on both the emitter and BSF (back surface field) sides. However, in production, nc-Si:H presents several challenges, particularly in terms of deposition rate, reproducibility and stability of layers and interfaces. This work presents a comprehensive study using advanced characterization of the properties of (p) nc-Si:H films grown in an industrial scale equipment. We have focused on studying different thicknesses and the impact of annealing on our layers, although we need very thin nc-Si:H layers to avoid parasitic absorption and reduce deposition time. Above 40 nm nc-Si:H seems to crystallize and stabilize its properties, while below this thickness we deal with a transition phase with evolution in crystalline fraction and properties giving a more unstable material. On the other hand, blisters appeared on layers with thicknesses over 60 nm due to hydrogen accumulation and material stress. Understanding the material properties can serve not only for SHJ but also for TCO-free recombination junction in tandems using nc-Si:H layers.