Recent progress on nanocellulose-based nanocomposites for application in photovoltaic solar cells and supercapacitors

The United Nations' Sustainable Development Goal number 7 aims to ensure access to clean and affordable energy for all. This has led to a global shift towards renewable energy sources that are readily available and sustainable. Solar technology and energy storage systems (ESSs) are important in transitioning to a more sustainable energy future. Solar technology has assisted in addressing environmental issues; however, its extensive commercial implementation has faced constraints due to several factors, including the significant installation area demands, use of endangered elements in the periodic table, high costs, intermittent operation/nature, limited durability, and associated efficiency losses. Petroleum-based nanomaterials, as electrodes, have been utilized, but their production and use have raised environmental and sustainability concerns. Thus, emerging high-value nanomaterials, such as nanocellulose extracted from abundant renewable and sustainable plants, have attracted significant attention. However, nanocellulose has limitations, such as low electrical conductivity and limited charge carrier mobility. To address these drawbacks, strategies such as surface modification, doping, hybridization with other nanomaterials, and optimization of processing techniques can help enhance the electrical conductivity, charge transport properties, surface area, porosity, and stability of nanocellulose. This review provides an overview of nanocellulose-based nanocomposites, their synthesis methods, and their physicochemical and electrical conductivity properties. In addition, it offers insights into the fascinating integration of nanocellulose with other carbon-based nanomaterials and metal oxides, and their impact on electrical conductivity properties. It is envisaged that this review will highlight and provide some directional trends on advancements in solar cells and capacitor devices.