Boron Doped Nanocrystalline Silicon as a Rear-Emitter in Silicon Heterojunction Solar Cells

The best silicon heterojunction (SHJ) solar cells show the potential of hydrogenated nanocrystalline silicon (nc-Si:H) to improve their performance on both the emitter and back surface field (BSF) sides. However, in production, nc-Si:H presents several challenges, particularly in terms of deposition rate, reproducibility and stability of layers and interfaces, as well as substrate selectivity and the amorphising nature of boron for p-type layers. A seed layer, such as (p) a-SiOx:H, can be introduced to promote nucleation of crystals and protect the passivation layers. In this work, a seed layer was optimized for SHJ integration using (p) nc-Si:H of different thicknesses and doping concentrations. Solar cell integration of (p) nc-Si:H deposited on the doped seed layer shows Voc and FF gains of +2.4 mV and +6.5%abs, respectively, compared to those with undoped seed layer. The best solar cells with (p) nc-Si:H as rear-emitter reached 22.2% of power conversion efficiency (PCE), only 0.7%abs lower than the (p) a-Si:H based reference, showing the potential of this material.