Synthesis and Characterization of Aluminum-doped ZnO Nanostructures via a Simple Solution Method for Effective Passivation of a Silicon Surface

Here, aluminum (Al)-doped zinc oxide (ZnO) nanostructures (AZO NSs) were synthesized via a chemical colloidal route with controlled structural, optical, photoluminescence (PL), and enhanced silicon (Si) surface passivation properties as a function of Al doping in the ZnO. Doping concentrations ranging from 2 at.% to 10 at.% Al were investigated. A dramatic change in the morphology of the AZO NSs was observed with varying Al doping concentrations. The undoped ZnO sample exhibited a particle-like morphology with a diameter of ~95 nm, which became flake-like structures and then hexagonal discs with an increase in the Al doping concentration. The band gap energy increased from 3.17 eV for undoped ZnO NSs to 3.28 eV corresponding to 2 at.% doped AZO NSs. In addition, defects consisting of zinc and oxygen vacancies/interstitials were minimized with Al doping, which was attributed to the replacement of Zn²⁺ ions by Al³⁺. Moreover, almost 15-fold enhancement in the passivation of the Si surface was exhibited by the optimized AZO NSs (4 at.%) as compared to the non-passivated Si surface and > 11-fold as compared to that of the undoped ZnO-coated Si surface. Effective surface passivation, thereby minimizing surface recombination, is one of the key requirements for efficient Si solar cells. Thus, the present study, reporting a simple synthesis route with improved structural, optical, PL, and surface passivation properties of AZO NSs as a function of Al doping, may pave the way for application in solar cells.