Zinc oxide nanostructures for third generation solar cells: A comprehensive review

As early as the 19th century, Svante Arrhenius established a correlation between rising CO₂ levels in atmosphere and increasing global surface temperatures. When Arrhenius published his work, he estimated an atmospheric CO₂ concentration of 300 ppm (Arrhenius, 1896). By the 1950s and 1960s, sensor measurements indicated a concentration of approximately 320 ppm (Keeling, 1960). Today, atmospheric CO₂ levels exceed 420 ppm. A significant portion of CO₂ emissions results from the combustion of fossil fuels. At every moment, the Earth’s surface is irradiated with approximately 170,000 terawatts (TW) from the Sun. This level of solar irradiance is significantly higher than what humanity requires to meet its energy demands. Photovoltaic solar energy, generated by photovoltaic devices that convert electromagnetic radiation from the sun in electricity, is considered a clean energy source capable of meeting society’s growing energy demands without emitting greenhouse gases. In this context, emerging photovoltaic technologies, or third-generation solar cells, have gained considerable attention due to their advancements towards large-scale implementation. A major advantage of third-generation solar cells, such as organic and perovskite solar cells, is the possibility to be fabricated with significantly less complex structures compared to conventional silicon-based cells. Nanostructures have been incorporated into these cells to enhance their efficiency and lifetime through optical, chemical and electronic mechanisms. This study aims to review the application of zinc oxide (ZnO) nanostructures – widely used in third-generation photovoltaic devices – and elucidate the mechanisms through which these nanostructures can improve the performance of third-generation solar cells.