The rapid development of low-power connected devices, widely used in fields such as the Internet of Things (IoT), building automation, smart agriculture, and wearables, has fueled research into novel technologies that can harvest energy from ambient sources and potentially store this energy, aiming to make these devices energy independent. A significant portion of the billions of IoT smart devices operates indoors, typically powered by batteries that require periodic recharging or disposal. This raises sustainability concerns related to maintenance and electronic waste production, highlighting the need for more efficient and self-sustaining solutions. As a result, there has been increased interest in developing indoor photovoltaics (IPV) for self-rechargeable IoT devices, addressing the limitations of traditional batteries and fostering the growth of large, energy-efficient IoT networks. [1] Moreover, the innovative concept of integrating photovoltaic cells for energy harvesting with an energy storage device, such as a supercapacitor (SC), to directly store this energy in a single unit is gaining recognition as a viable and sustainable alternative to batteries for powering low-power IoT devices. [2],[3] In this contribution, we address the sustainability of such integrated devices by selecting green, sustainable, and low-toxic materials that can be shared between the photovoltaic cell (i.e., a dye-sensitized solar cell, DSSC) and the supercapacitor, with a particular focus on their application in indoor environments. We demonstrate, for the first time, that γ-valerolactone (γ-VL), a sustainable, low-toxic solvent derived from cellulosic biomass, can be used for the preparation of the DSSC electrolyte as an alternative to more common but toxic and flammable solvents such as acetonitrile (ACN) and 3-methoxypropionitrile (MPN). Recently, γ-VL has also been shown to be well-suited for the preparation of high-voltage supercapacitors. [4] Our results indicate that γ-VL is unsuitable for outdoor DSSCs due to slower ion diffusion and reduced I₃^- reduction at the counter electrode. However, γ-VL-based DSSCs outperform those using ACN and MPN under indoor light (1000 lux), demonstrating equivalent short-circuit currents but with higher open-circuit voltages, improved fill factors, and enhanced overall efficiency, enabled by lower recombination at the photoanode. Thanks to the compatibility of γ-VL with both technologies, we fabricated an integrated energy harvesting and storage device using γ-VL for electrolyte preparation. Moreover, we also demonstrate that the same carbon-based materials used for the SC electrodes are also suitable as counter electrodes for the DSSC. The fabricated integrated harvesting and storage device showed optimal self-charging capabilities and stability under indoor illumination conditions, achieving high charging voltage and good charge retention over time, making it a promising alternative to disposable batteries for IoT devices.