Development and Optical Properties of ZnO Nanoflowers on Porous Silicon for Photovoltaic Applications

In the present work, a comparison between zinc oxide (ZnO) nanoflowers and nanorods for photovoltaic applications is presented. Using chemical bath deposition technique, ZnO nanoflowers were grown on porous silicon (PS) while ZnO nanorods were deposited on flat Si substrate. The morphology of ZnO/PS sample indicated the formation of nanoflowers by accumulation of ZnO nanorods on PS walls. The structural studies indicated that ZnO nanoflowers experienced a stress relief compared to ZnO nanorods which was due to the role of porous substrate for accommodating the lattice strain in order to obtain the subsequent ZnO nanoflowers with reduced strain. The optical results obtained from ZnO nanoflowers showed more intense photoluminescence and Raman peaks compared with nanorods. It was due to the higher specific surface area of nanoflowers which led to a higher absorption coefficient and increased the generation of electron–hole pairs in this sample. Due to their elevated specific surface area, ZnO nanoflowers can capture the incident light and reduce the reflection coefficient of silicon substrates. Thus, they can be considered as an effective antireflective layer to improve the efficiency of solar cells. The optoelectrical results showed an improvement in the efficiency of fabricated solar cells by use of ZnO nanoflowers on PS structures when compared to the conventional ones possessing ZnO nanorods on flat silicon substrates. Development of ZnO nanoflowers on PS substrates can further extend the applications of ZnO nanostructures in photovoltaic devices.