A strategy for utilizing hollow polyoxometalate nanocrystals to improve the efficiency of photovoltaic cells

Polyoxometalates have been proved to be the significant electronic transfer medium to improve the power conversion efficiency of dye-sensitized solar cells based on our previous works. However, the morphology of polyoxometalates dramatically affects the photovoltaic performance of dye-sensitized solar cells. In this work, we develop a strategy of utilizing hollow polyoxometalate nanocrystals to improve the efficiency of dye-sensitized solar cells. The hollow polyoxometalate nanocrystals and rhombic dodecahedral polyoxometalate nanocrystals are synthesized and then composited with TiO2 to obtain two kinds of high dispersed polyoxometalate nanocrystals composites. The images of transmission electron microscopy and element mappings confirm that hollow polyoxometalate nanocrystals and rhombic dodecahedral polyoxometalate nanocrystals are uniformly distributed in TiO2 composites. The improved morphology with well-defined structures may provide more active sites for polyoxometalates to achieve faster charge separations and less charge recombinations in dye-sensitized solar cells. In addition, the films with hollow polyoxometalate nanocrystals have better dye loading than those with pristine TiO2. Finally, the dye-sensitized solar cells based hollow polyoxometalate nanocrystals and rhombic dodecahedral polyoxometalate nanocrystals exhibit the efficiency of 8.06% and 7.28%, respectively, which are 34% and 21% higher than those based pristine TiO2 (6.00%).