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

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 Δ E V and large Δ E 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 Ni 2+ , and moreover, the introduction of Ag + also increased the amount of Ni 3+ 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%.