Investigation of n-Al:ZnO/p-Cu2O heterojunction for c-Si tandem heterojunction solar cell applications

Abstract

In this work, an in-situ growth approach has been employed to fabricate Al:ZnO/Cu2O/Cu and Al:ZnO/ZnO/Cu2O/Cu heterojunctions using direct current (DC) and radio frequency (RF) magnetron sputtering technique in a controlled atmospheric condition. The effect of ZnO buffer layer thickness (30 and 50 nm) as well as in-situ Cu2O annealing at 600 °C in low vacuum (~ 10−6 Torr) prior to Al:ZnO deposition were studied. The carrier density of Al:ZnO was ~2 × 1020 cm3 with mobility ~8 cm2/V·s and resistivity ~1 × 10−3. Ω·cm, while the carrier density of Cu2O was 1 × 1015 cm3 with mobility ~19 cm2/V·s and resistivity ~200 .Ω·cm. The heterojunctions were investigated by depth resolved Cathodoluminescence (CL) spectroscopy at 80 K to analyze the influence of defects at the interface. The two emissions at 1.51 eV (Vo+) and 1.69 eV (Vo2+) dominate in all CL spectra related to oxygen vacancy defects in Cu2O. The relative intensity of the defect luminescence band Vo+ respect to Vo2+ is greater at the interface compared to bulk Cu2O, while the incorporation of the ZnO layer reduces significantly both radiative recombination and the Vo2+ related emission at the interface.