Monolithic Quasi-Solid-State Dye Sensitized Solar Cells Prepared Entirely by Printing Processes

A complete printing process was developed to fabricate the quasi-solid-state dye-sensitized solar cells with monolithic structures (m-QS-DSSCs). First, a structure of m-DSSCs was constructed by sequentially printing TiO₂ layers (main and scattering), a ZrO₂ insulating layer, and a carbon counter electrode (CE) onto an FTO substrate (FTO/TiO₂/ZrO₂/carbon CE). Then, a quasi-solid-state printable electrolyte (QS-PE), prepared using polyethylene oxide/polymethyl methacrylate, was printed directly on top of the porous carbon counter electrode (CE), enabling the m-QS-DSSCs to be prepared entirely by printing processes. In this study, the porous structures and characteristics of the ZrO₂ and carbon layers were optimized by controlling the film thicknesses and heat treatment conditions; furthermore, the Pt layer was coated to improve the catalytic activity of carbon CEs. The results revealed that an appropriate porous structure of carbon and ZrO₂ films could be obtained by heating the films from 200 to 500 °C. Through these porous layers, the QS-PE can penetrate well into the photoelectrodes, increasing the charge transport in the cells and at the electrode/electrolyte interfaces; therefore, the m-QS-DSSCs can achieve an efficiency of 6.79% under 1 sun illumination. Furthermore, the structures can also be utilized to fabricate liquid cells for application in a dim light environment. The m-QS-DSSCs remained stable during a long-term stability test at room temperature.