Solar energy is a cornerstone of the future global sustainable energy system. The book chapter outlines how performance and energy yield increase will have to evolve concurrently to make PV a major electricity source and how PERC-technology is an important milestone in achieving this.

The author focuses on the surface passivation mechanism of Al₂O₃ and how it is related to its material properties. The chapter starts off with a short description of the fundamentals of surface recombination stressing the importance of the electronic properties of the c-Si/Al₂O₃ interface with respect to defect density and fixed charge. Next, an overview is presented of the electronic properties for Al₂O₃ layers synthesised on c-Si substrates by various techniques. Finally, these electronic properties are related to the atomic-scale material properties for Al₂O₃ films with a particular focus on the, typically unintentional, presence of an interfacial silicon oxide film.

The authors review developments in the use of PECVD in the growth of AlO_x layers for solar cells. They consider the microwave PECVD and inductively coupled plasma PECVD methods, and the characteristics of layers grown by the 2 techniques, Si surface passivation, and solar cell applications.

The author provides a historical review of research into the atmospheric pressure chemical vapour deposition (APCVD) of Al₂O₃ for silicon surface passivation in solar cell devices, considering deposition temperature influence on excess carrier lifetime, film thickness and interface state density.

In this book chapter the properties of Al₂O₃ based p⁺ surface passivation is described, focusing on the impact of deposition conditions, annealing sequence, capping layer material, Al₂O₃ thickness, and surface morphology.

Over recent decades, surface-passivating properties of PECVD a-SiN_x:H have been investigated extensively. These properties depend on the number of fixed charges (Q_f) and interface density of states (D_it) and are in turn related to bulk and interface properties. In general, there is a positive correlation between Q_f and D_it, which have opposite effects on the surface-passivating properties. For an optimal effective surface passivation, an optimization is therefore necessary. Higher Q_f and D_it are found to correspond to a higher and deeper insertion of N in c-Si thereby increasing the concentration of these defects. This insertion is related to NH₃ flow and temperature during plasma treatment. This technique for forming defect layers has been experimentally validated by EELS as well as high resolution TEM. MD simulation and ab initio DFT studies demonstrated the formation of defects and higher DOS in the bandgap for the same layer composition. Introduction of hydrogen was simulated with DFT as well and showed a lower DOS in the bandgap resulting in a better surface passivation. The effect of Q_f at the interface on the passivating properties of a-SiN_x:H applied to completed solar cells was proven as well and confirmed by PC1D device simulations.

In this book chapter it is shown that Al₂O₃ deposition systems based on spatial ALD with wafer floatation are attractive for passivation of cSi solar cells in high-volume manufacturing. In principle, the throughput can be increased to 7,200 wafers/h; the limitation is not the ALD track, but the unloading automation.