Solar and Triboelectric Energy Generators Using Eco-Friendly Materials and Resource-Efficient Processes

The dwindling supply of non-renewable sources of energy and the massive environmental damage caused by the techniques used to retrieve these resources, makes it necessary to explore renewable energy using cheap and obtainable resources. Whilst considerable advances have been made in the field of reneawable energy harvesting, the energy harvesters are not always developed using eco-friendly materials and scalable resource-effcient processes. Further, there has been little consideration for the development of energy generators that can be safely decomposed into non-toxic by-products after their end-of-life. We have developed different types of energy harvesting devices using sustainable and biodegradable materials and processes which could address the above-mentioned challenges. Here we focus on two such energy harverstors: The first type is a transient triboelectric nanogenerators (T-TENGs), fabricated using degradable Poly-L-lactic acid (PLLA) fibres and chitosan as the active triboelectric layers. We have used both the aligned-PLLA and random-PLLA fibers and compared their performance to understand the impact of fibres alignment on the energy output performance. The aligned-PLLA fibre based T-TENGs are found to exhibit superior performance (output voltage and current of 45 V and 9 μA, respectively) due to better 103 helix chain conformation. The T-TENG showed excellent mechanical stability for 24000 cycles and produced an output power density of 6.5 mW m^-2. The soil burial test confirms the degradation of the materials used in the device fabrication. The second type of energy devicea are the miniaturised (≈315 µm²) indoor light energy harvesters or microcells developed using resource-efficient and scalable printed manufacturing route. The p–i–n active light harvesting layer is developed using Si nanoribbons that were fabricated using a top–down method followed by direct roll printing on flexible polyimide substrate. Using a set of 32 microcells, connected in parallel configuration, indoor light harvesting is shown at a maximum power density of ≈10 µW cm⁻² under white LED illumination. These microcells are also able to perform wideband photodetection at zero bias, demonstrating the dual functionality of developed photovoltaic microcells. The presented results show the potential usage of multifunctional microcells as self-powered wearable and flexible sensors for health monitoring and indoor robotics.