Excellent crystalline silicon surface passivation by transparent conductive Al-doped ZnO/ITO stack.

[Display omitted] • ALD AZO/sputtered ITO stack shows an excellent passivation effect on Si surface. • The sheet resistance of the AZO/ITO stack is only about 90 Ω/sq. • AZO/ITO stack shows outstanding antireflection effect and no parasitic absorption. • ITO as a cover layer effectively prevents the effusion of H atoms from the AZO. • AZO doping level affects crystalline silicon surface passivation. The surface passivation materials commonly used in crystalline silicon (c-Si) solar cells are either electrically insulating or opaque to the solar spectrum, which poses the electrical loss or optical loss. Hence it is of great significance to explore functional films that are simultaneously transparent, conductive and passivating for c-Si. In this study, we successfully tune two most well-known transparent conductive oxides, i.e. Al-doped ZnO (AZO) and indium tin oxide (ITO), as excellent passivation layers for c-Si surface. The AZO film is grown by atomic layer deposition and is capped with a magnetron-sputtered ITO film. Dynamic secondary ion mass spectrometry reveals that such stack design can retain higher hydrogen concentration on c-Si surface than a single AZO film during annealing. In addition, the AZO should be highly doped to reduce the energy barrier height around c-Si surface, thereby increasing the charge carrier asymmetry and thus reducing surface recombination. It is also highly crucial to optimize the annealing temperature and interfacial silicon oxide. As such, the effective minority carrier lifetime reaches 2.0 ms and the implied open-circuit voltage approaches 700 mV. Besides, the AZO/ITO stacked films possess negligible optical absorption, low sheet resistance (∼90 Ω/sq), and outstanding antireflection effect on c-Si surface. [ABSTRACT FROM AUTHOR]