Functionalized Thermoplastic Polyurethane Gel Electrolytes for Cosensitized TiO2/CdS/CdSe Photoanode Solar Cells with High Efficiency

A polymer gel electrolyte has been developed based on functionalized thermoplastic polyurethane for solar cell devices. Long-chain polyurethane is synthesized, and subsequently, a small pendant moiety having a sulfonate group has been attached to convert the hydrophobic polyurethane into hydrophilic and conducting, suitable for solar cell applications. The functionalization has been confirmed through spectroscopic techniques such as H-1 NMR, Fourier transform infrared, and UV-vis studies. The ionomer-functionalized polyurethane is found to be anticorrosive (high inhibition efficiency) and is expected to improve the durability of the solar cell. The quantum dots of CdS- and CdSe-based sensitizers have been prepared using a capping agent to avoid agglomeration. Light-harvesting capability is found to be the highest in the case of cosensitizers as opposed to individual sensitizers. Cyclic voltammetry and optical band gap measurement through UV studies have been performed to measure the energy levels of the highest occupied molecular orbital, lowest unoccupied molecular orbital, valence band (VB), and conduction band (CB) for polymers and quantum dots and thereby optimize the best possible combination of materials based on the matching of energy levels along with the electrodes. Solar cells have been fabricated using optimized cosensitizers and TiO2 /CdS/CdSe as the photoanode, appropriately functionalized polyurethane as the gel electrolyte, and platinum as the counter electrode through the layer-by-layer deposition technique. The cosensitized system exhibits the highest energy conversion efficiency of 1.5% because of better charge carrier transport following the close proximity of the energy level of suitable quantum dots of proper dimension and appropriate functionalization of polyurethane. The device is found to be durable with similar efficiency at a longer time period. The functionalized thermoplastic polyurethane gel electrolytes play a crucial role in enhancing the power conversion efficiency and long-term stability of the fabricated solar cell.