ZnO nanorod hemispherical light scatterers for thin film solar cell applications

Efficient light management is crucial for enhancing the performance of thin film solar cells. This study investigates the use of solution-processed ZnO nanorod arrays with novel hemi-spherical nanostructures as light scatterers for thin film solar cell applications. The morphology of the ZnO nanorod arrays is controlled by varying the seed layer deposition method (slot-die coating vs. physical vapour deposition) and thickness. A thin slot-die coated seed layer (i.e. ~100 nm) promotes the formation of hemi-spherical nanostructures, which exhibit enhanced light scattering properties compared to vertically aligned nanorods grown on physical vapour deposition seed layers. This study reveals that an in-plane stress induced by lattice mismatches along the c-axis of nanorods causes the thin seed layer to arch upwards and develops these hemi-spherical light scatters. COMSOL simulations further reveal that the enhanced scattering is due to a combination of total internal reflection and refraction within the nanorod arrays. The deposition of a CdS buffer layer on the hemi-spherical arrays further improves light scattering, achieving a high average haze value of 0.72 in the wavelength range of 400 nm to 1000 nm. Bringing together light scattering features of these structures, SCAPS simulations demonstrate incorporating ZnO nanorod hemi-spherical light scatters into CdTe solar cells can significantly enhance photogenerated carrier collection, potentially enabling thinner absorber layers and reduced material consumption. This work offers a promising pathway towards cost-effective and high-efficiency thin film solar cells through innovative nanostructure design and solution-based fabrication techniques.