Improving the photoelectrical conversion efficiency of silicon solar cells using ZnO:Al/porous silicon double antireflective layers

Abstract

In this work, porous silicon (PS) layers are performed on the front side of $${\text{n}}^{ + } {\text{p}}$$ wafer via electrochemical etching technique (etching times of 15 and 25 min), using isopropanol as solvent, followed by covering with Al-doped ZnO (AZO) films prepared by sol–gel spin-coating method. AZO/PS double layers are found to have incomparable photoluminescence and reflectance characteristics required for the use as antireflection. The structural, optical properties of PS, AZO and AZO/PS have been investigated. The results show that the energy bandgap of PS layer is higher than that of nonporous Si and increases slightly with increasing the etching time. X-ray diffraction shows that the prepared AZO films have nanostructure character with hexagonal structure. The optical properties of AZO films are studied in terms of measuring the transmittance and reflectance over wavelength range 200–2500 nm. Using these parameters, the absorption coefficient and refractive index of AZO films are calculated and the related parameters are estimated. AZO films deposited on PS/$${\text{n}}^{ + } {\text{p}}$$ exhibit low reflectance compared to $${\text{n}}^{ + } {\text{p}}$$ and AZO/$${\text{n}}^{ + } {\text{p}}$$ systems. The improvement of the solar cells performance due to the effect of porosity and AZO films deposition are investigated in which the solar cells parameters are evaluated and discussed.