This chapter discusses the role that hydrogen takes in the passivation of silicon surfaces. The basic concepts of surface recombination and passivation are first introduced, to then examine how hydrogen can influence the dynamics of charge carriers at the surface of silicon. The different materials and synthesis techniques used to achieve optimal surface passivation are covered. In particular, the role of hydrogen in all materials and detection techniques are reviewed in detail, drawing on the latest findings in the field. Hydrogen-mediated passivation is examined in silicon dioxide (SiO2) thin films, as well as in hydrogen-containing dielectric layers, such as plasma-enhanced chemical vapour deposition (PECVD) silicon nitride (SiNx), PECVD amorphous silicon (a-Si), and atomic layer deposition (ALD) or PECVD aluminium oxide (AlOx). The role of silicon oxide and nitride are examined at length, as these materials are of critical importance to the development of photovoltaic (PV) technology. SiNx is the most widely adopted surface coating in the solar cell industry, and this has been largely due to its hydrogenation benefits and suitability as an antireflection coating. The use of thermal processes in releasing hydrogen from the dielectric are also covered, since such steps serve in the activation of surface passivation, or in the injection of hydrogen into the silicon material for bulk passivation. Last, the latest developments of hydrogenation in tunnelling oxide passivating contacts are reported, and an outlook summary is provided on the vital role that hydrogenation processes will take in the future improvement of silicon PV devices.
