Size-controlled synthesis of ZIF-8 particles and their pyrolytic conversion into ZnO aggregates as photoanode materials of dye-sensitized solar cells

We have proposed a fabrication process of submicrometer-sized zinc oxide aggregates with nano/microstructures through pyrolysis of ZIF-8 particles. Methanol solutions of zinc nitrate hexahydrate and 2-methylimidazole were used for synthesizing ZIF-8 with its characteristic rhombic dodecahedron morphology. The systematic addition of 1-methylimidazole to the above methanol solutions led to the formation of size-tunable ZIF-8 particles. Precise control of heating conditions was a key to successful conversion from ZIF-8 to ZnO without destroying the morphology. The ZnO aggregates thus obtained were evaluated as photoanode materials of dye-sensitized solar cells. A photoanode using a 9 μm thick ZnO aggregate film gave a power conversion efficiency of 3.37% due to its nano/microstructures being suitable for dye adsorption, electrolyte diffusion, and light harvesting.