Harnessing γ‐Valerolactone: Green and Low‐Toxic Solvent for Enhanced Dye‐Sensitized Solar Cells Performance Under Indoor Lighting

A significant portion of the billions of Internet of Things (IoT) smart devices operate indoors, typically powered by batteries that require periodic recharging or disposal, raising sustainability concerns about maintenance and electronic waste production. This has generated increased interest in developing indoor photovoltaics (IPV) for self-rechargeable IoT devices. Among IPV technologies, dye-sensitized solar cells (DSSCs) offer high conversion efficiency, stability, and scalability. However, the use of toxic and flammable solvents, such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN), remains a concern. This research investigates γ-valerolactone (γ-VL), a sustainable, low-toxic solvent derived from cellulosic biomass, as an alternative for DSSC electrolytes. Electrolytes based on I−/I3− redox shuttle are prepared with γ-VL, MPN, and ACN and studied in both dummy cell and full device configuration. Results show that γ-VL is unsuitable for outdoor DSSCs due to slower ion diffusion and reduced I3− reduction at the counter electrode. However, γ-VL DSSCs outperform those using ACN and MPN under indoor light, demonstrating equivalent short-circuit currents but higher open-circuit voltages, improved fill factors, and enhanced overall efficiency, enabled by lower recombination at the photoanode. These findings position γ-VL as a promising, eco-friendly option for DSSC electrolytes in indoor IoT applications.