A novel silver-doped nickel oxide hole-selective contact for crystalline silicon heterojunction solar cells

Abstract

Based on its band alignment, p-type nickel oxide (NiO_x) is an excellent candidate material for hole transport layers in crystalline silicon heterojunction solar cells, as it has a small ΔE_V and large ΔE_C with crystalline silicon. Herein, to overcome the poor hole selectivity of stoichiometric NiO_x due to its low carrier concentration and conductivity, silver-doped nickel oxide (NiO_x:Ag) hole transport layers with high carrier concentrations were prepared by co-sputtering high-purity silver sheets and pure NiO_x targets. The improved electrical conductivity of NiO_x was attributed to the holes generated by the Ag⁺ substituents for Ni²⁺, and moreover, the introduction of Ag⁺ also increased the amount of Ni³⁺ present, both of which increased the carrier concentration in NiO_x. Ag⁺ doping also reduced the c-Si/NiO_x contact resistivity and improved the hole-selective contact with NiO_x. Furthermore, the problems of particle clusters and interfacial defects on the surfaces of NiO_x:Ag films were solved by UV-ozone oxidation and high-temperature annealing, which facilitated separation and transport of carriers at the c-Si/NiO_x interface. The constructed c-Si/NiO_x:Ag solar cell exhibited an increase in open-circuit voltage from 490 to 596 mV and achieved a conversion efficiency of 14.4%.

Key words： band alignment; nickel oxide; hole transport layer; silver-doped nickel oxide; UV-ozone

Competing interests

The authors declare that they have no competing interests.

Acknowledgements

This work is supported by the National Natural Science Foundation of China (Grant No. 61974076), and the China National Key R&D Program (Grant No. 2022YFC2807104).

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11705-024-2384-6 and is accessible for authorized users.

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