ALD Al2O3 based nanolaminates for solar cell applications

Al₂O₃ based nanolaminates provide new functionalities for silicon surface passivation layers in future high-efficient cell concepts. This work presents two different applications: (I) Symmetrical passivation layers for application on p- and n-type Si are realized with thin HfO₂ and Al-doped SiO₂ interface layers between Al₂O₃ and Si. These stacks have excellent chemical passivation but zero fixed charges. Consequently, no surface inversion layer is formed in n-type Si and low surface recombination velocities below 2 cm/s are achieved in low injection. (II) Conductive passivation layers are realized with Al₂O₃-TiO₂ double and multilayers. The optimum material combination and post deposition treatment results in a current density of 0.5 mA/cm² at 10 mV with a surface recombination velocity of about 15 cm/s. This conductivity is more than eight orders of magnitude higher than for pure Al₂O₃.