Passivation analysis of silicon surfaces via sol—gel derived Al-rich ZnO film

Abstract

Electronic recombination losses can be reduced via passivation of silicon surfaces. Most techniques available in the literature are either not cost effective or not applicable for solar cell applications. We investigate low cost sol–gel derived Al-rich zinc oxide (ZnO:Al) film and its effective passivation of p-type silicon surfaces. Herein, we present the elemental composition of the film and interfacial structure of ZnO:Al/Si using FTIR, XPS, TEM, and SIMS characterizations. ZnO:Al is polycrystalline and contains some very small amorphous regions of Al2O3. At the ZnO:Al/c-Si interface, a thin SiOx layer with a thickness of ∼6 nm is formed. The XPS analyses reveal that the Al/Zn molar ratio in the ZnO:Al increases from ∼10% at the surface to ∼80% at the ZnO:Al/c-Si interface. The hydrogen content also gradually increases from the surface to the interface. The FTIR absorption area corresponding to the Si–H bonding is ∼2.89 au. The obtained hydrogen concentration is ∼3.93 × 1022 atoms cm−3. A fixed negative charge is created by ZnO:Al on ZnO//SiOx interface. The thermal equilibrium was established between Si and ZnO:Al through SiOx by electron tunneling current. Here, the c-Si may be passivated for two reasons: (i) Al creates defects on the ZnO:Al/c-Si interface and H is attached to the defects (dangling bonds) and (ii) due to the field effect passivation via the negative charged ZnO:Al film.