Highly effective electronic passivation of silicon surfaces by atomic layer deposited hafnium oxide

This paper investigates the application of hafnium oxide (HfO₂) thin films to crystalline silicon (c-Si) solar cells. Excellent passivation of both n- and p-type crystalline silicon surfaces has been achieved by the application of thin HfO₂ films prepared by atomic layer deposition. Effective surface recombination velocities as low as 3.3 and 9.9 cm s⁻¹ have been recorded with 15 nm thick films on n- and p-type 1 Ω cm c-Si, respectively. The surface passivation by HfO₂ is activated at 350 °C by a forming gas anneal. Capacitance voltage measurement shows an interface state density of 3.6 × 10¹⁰cm⁻² eV⁻¹ and a positive charge density of 5 × 10¹¹cm⁻² on annealed p-type 1 Ω cm c-Si. X-ray diffraction unveils a positive correlation between surface recombination and crystallinity of the HfO₂ and a dependence of the crystallinity on both annealing temperature and film thickness. In summary, HfO₂ is demonstrated to be an excellent candidate for surface passivation of crystalline silicon solar cells.