Influence of ZIF-8 modification on performance of ZnO-based dye-sensitized solar cells

Metal–organic frameworks (MOFs) were used to modify the surface of nanoparticulate ZnO electrodes, aiming at enhancing the performance of dye-sensitized solar cells (DSSCs). Zeolitic imidazolate framework-8 (ZIF-8) consisting of Zn 2+ ions and 2-methylimidazolates was chosen and their concentrations in precursor solutions were set as experimental conditions for the MOF-modification. A thin ZIF-8 layer with a thickness of 3 nm could be formed on the ZnO surface by immersing the ZnO film in a high-concentration precursor solution at room temperature, as confirmed by field-emission transmission electron microscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. However, both short-circuit photocurrent density ( J SC ) and open-circuit photovoltage of the cell using the above ZIF-8-modified electrode were decreased probably because of the inhibition of the electron injection from photoexcited dyes. In contrast, the immersion of the ZnO film in a low-concentration precursor solution was found to be effective in enhancing J SC , which was explained by the improved charge transfer through the surface passivation of the ZnO electrode. Another positive effect was the improved durability observed in the cell using the modified electrode.