Dye-sensitized solar cells based on a single layer deposition of TiO ₂ from a new formulation paste and their photovoltaic performance

A new strategy for enhancing the efficiency and reducing the production cost of TiO ₂ solar cells by design of a new formulated TiO ₂ paste with tailored crystal structure and morphology is reported. The conventional three- or four-fold layer deposition process was eliminated and replaced by a single layer deposition of TiO ₂ compound. Different TiO ₂ pastes with various crystal structures, morphologies and crystallite sizes were prepared by an aqueous particulate sol-gel process. Based on simultaneous differential thermal (SDT) analysis the minimum annealing temperature to obtain organic-free TiO ₂ paste was determined at 400°C, being one of the lowest crystallization temperatures of TiO ₂ photoanode electrodes for solar cell application. Photovoltaic measurements showed that TiO ₂ solar cell with pure anatase crystal structure had higher power conversion efficiency (PCE) than that made of pure rutile-TiO ₂. However, the PCE of solar cells depends on the anatase to rutile weight ratio, reaching a maximum at a specific value due to the synergic effect between anatase and rutile TiO ₂ nanoparticles. Moreover, it was found that the PCE of solar cells made of crystalline TiO ₂ powders was much higher, increasing in the range 32-84% depending on anatase to rutile weight ratio, than that of prepared by amorphous powders. TiO ₂ solar cell with the morphology of mixtures of nanoparticles and microparticles had higher PCE than the solar cell with the same phase composition containing TiO ₂ nanoparticles due to the role of TiO ₂ microparticles as light scattering particles. The presented strategy would open up new insight into fabrication and structural design of low-cost TiO ₂ solar cells with high power conversion efficiency.