Review on Functional Electrolyte, Redox Polymers, and Solar Conversions in 3G Emerging Photovoltaic Technologies: Progress and Outlook

Abundant solar energy has transformed the present solar photovoltaics owing to its rapid conversion into electrical energy without deteriorating ecosystem. Third generation (3G) energy conversion devices reveal utilization of photosensitizer, i.e., organic dye, quantum dots, and perovskite as functional absorbing materials to transform solar energy. Functional polymers are key ingredients (fuels) for the development of suitable redox potential and high temperature or humidity resistive charge transport medium. Electrolyte accelerates the photovoltaic reversible reaction (hole conduction) through exposure of a minimum energy barrier between the photoanode and cathode. Redox-active polymer enhances electrolyte uptake efficiency, ionic conductivity, and dimensional stability of solar device. Various electrolytes exhibit different functional activities due to their different redox energy. The functionalized polymer bears appropriate HOMO–LUMO energetics and low activation energy, which could adjust different photosensitizer with better compatibility. Therefore, the redox polymer percolates a redox couple at a photoexcited sensitizer through control of undesired reactions. It plays the important role of ion and electron transport mediator via expanding suitable interfacial energetics and band structure for photovoltaic reaction. The polymeric pendant groups (chemical environments) preserve electrolyte couples through reducing wettability and thus immobilize the active density of electrolyte anions for photovoltaic reactions. Thus, the polymer improves reversibility due to interfacial compatibility, electrolyte filtration effect, and synergistic stabilization. The present review focuses on polymer-derived functional electrolytes, photosensitizer–polymer interface, thermodynamic interactions, and power conversion efficiencies of 3G photovoltaic devices. Functional polymers open an avenue for the development of stable and efficient photovoltaic reactions at low cost based dyes, quantum dots, and perovskite-sensitized solar conversion systems.