Oxygen vacancies facilitated hole transport in ZrO2 films by Al3+ doping for p-Si heterojunction solar cells

Transition metal oxides (TMOs) have attracted considerable attention for carrier-selective passivation contacts in crystalline silicon (c-Si) heterojunction solar cells. Among them, zirconium dioxide (ZrO2) exhibits outstanding advantages, such as high permittivity, the presence of fixed negative charges, and high thermal stability. However, it is usually considered incapable of being used as passivation contacts due to its ultra-wide (5.8 eV) bandgap and mismatched energy band structure. In this work, we have demonstrated that ZrO2 films act as hole-selective layers by elaborately regulating oxygen vacancies (VO). ZrO2 films (∼9 nm) prepared by the solution method provide a high surface passivation of p-Si with an effective carrier lifetime of 302 μs. The Al3+ doping not only increases the VO concentrations in the films but also changes the ratio of different categories of VO defects, significantly improving the hole transport properties, with the contact resistivity reduced from 246 to 52 mΩ·cm2. The p-Si/ZrO2:Al3+/Ag structured solar cell reaches a high conversion efficiency of 19.5%. This work shows that ultra-wide bandgap semiconductor materials have great potential as passivation contact layers by modulating the trap defects.