Annealing-free, Electron-Selective Ohmic Contacts Using Zirconium Oxide and Aluminum for N-Type Crystalline Silicon Solar Cells

The challenge of Fermi-level pinning significantly complicates the establishment of Ohmic, low-resistance contacts for lightly doped n-type crystalline silicon (c-Si), a critical requirement for economically feasible device development. In this novel study, we present an innovative approach by introducing an ultra-thin zirconium oxide (ZrOx) film to achieve an Ohmic contact in n-type c-Si. The ZrOx films are deposited through e-beam evaporation at room temperature, and their properties are characterized using spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and contact resistivity (rho c) measurements. Our investigation unveiled a pronounced dependence of the contact resistivity on the thickness of the ZrOx layer, with the lowest rho c value of 22 m Omega cm2 achieved with an ultrathin 1 nm ZrOx film. To demonstrate our study's feasibility, we applied ZrOx as an electron-selective rear-side contact layer in a lightly doped n-type c-Si solar cell with a boron-diffused emitter on the front side. This yielded a photovoltaic conversion efficiency (PCE) of 16% and a notable fill factor (FF) exceeding 79%. These findings clearly emphasized the significant promise of ZrOx as an emerging and highly effective electron-selective contact layer for lightly doped n-type c-Si devices.