UC Riverside

Solar energy has the highest potential of the Earth´s renewable energy sources. Its conversion into electrical power to meet the demand of our economy is an ongoing effort. The leading technology, silicon, and the emerging alternative technologies, like CdTe and perovskites, require energy intensive manufacturing processes, toxic chemicals and/or non-abundant minerals that cause problems thorough their life cycle such as pollution and social conflicts. Since the negative impacts of PV technology are mainly derived from material selection and manufacturing processes, new advanced technology that uses abundant, renewable and biodegradable materials, as well as cleaner fabrication processes needs to be developed for the sustainable future of solar energy. Carbon is an abundant element that exhibits a broad assortment of allotropic forms and electrical behavior, and can make up an infinite variety of functional biomolecules when combined with other plentiful elements. We propose the combination of graphene-ZnO hybrids with a phototrophic protein, bacteriorhodopsin (bR), to develop a bio-sensitized solar cell. The graphene is used to replace the tin oxide transparent conductor in the photanode, while the bR is used to replace the traditional synthetic dyes that absorb the visible sunlight. Two different morphologies and fabrication approaches of nano-ZnO are investigated to create graphene heterostructures for photoanode platform: commercial nanoparticles and vertical nanorods in situ grown by electrodeposition. The immobilization of the bR on the ZnO and the mediator selection are optimized in function of the photoelectric response of the system. We investigate the structure, energy alignment and electrical behavior at the different interfaces of the device, graphene/ZnO/bR/electrolyte, and correlate them to processing parameters. The photovoltaic performance, internal resistance and electron kinetics of the cells are characterized by photo-electrochemical methods. The introduction of heterostructures using carbon nanomaterials and biomolecules derived from renewable sources together with low cost, non-toxic semiconductors constitute the beginning of a new era for sustainable bio-photovoltaics, which is supported by the latest advances in genetic engineering and nanotechnology. This work demonstrates the viability of sustainable alternatives to replace traditional costly and harmful materials and provides a framework to the design of novel bio-nanointerfaces for future technological applications.