Influence of H2O/DEZ ratio on LPCVD ZnO:B films for application in a-Si:H/μc-Si:H tandem solar cells

Abstract

In this study, boron doped zinc oxide (ZnO:B) films were prepared at different water to diethyl zinc (H2O/DEZ) flow ratios from 0.6 to 1.4 by a low pressure chemical vapor deposition (LPCVD) technique. It is found that the morphology of ZnO:B films varies from small leaf-like to pyramidal surface structures with the increasing H2O/DEZ flow ratio. The rough ZnO:B films deposited at a relatively H2O/DEZ flow ratio such as 1.2 or 1.4 show a high haze value of up to 28 % at 600 nm and \(\mathrm{a} (11\overline{2}0)\) preferential crystallographic orientation. All ZnO:B films were applied in hydrogenated amorphous silicon/microcrystalline silicon tandem solar cells (a-Si:H/μc-Si:H) as front electrodes. The efficiency of the solar cells increases with the increasing H2O/DEZ flow ratio, which is attributed to a high spectral response mainly in the long-wavelength range and the consequent enhancement of short-circuit current. A high-efficiency a-Si:H/μc-Si:H tandem solar cell of 10 % was achieved. The H2O/DEZ ratio is an important process parameter to tune the material properties of LPCVD ZnO:B films and the performances of corresponding silicon thin film solar cells.