Atmospheric-pressure-plasma-jet sintered dual-scale porous TiO2 using an economically favorable NaCl solution

• Dual-scale porous TiO2 was prepared by screen-printing and APPJ-sintering.
• A low-cost NaCl solution was added into the TiO2 nanoparticle pastes.
• During APPJ sintering, NaCl crystals precipitated as molds for large cavities.
• DI water rinsing dissolved NaCl to form large cavities in nanoporous TiO2.
• DSSCs with dual-scale porous TiO2 photoanodes show improved performance.

We have developed a rapid atmospheric pressure plasma jet (APPJ) sintering process for nanoporous TiO2 containing large cavities (of the order of a few hundreds of nanometers to a few micrometers) using an economically favorable NaCl solution. Screen-printing was used to administer mixed pastes consisting of TiO2 nanoparticles and NaCl solutions, following which APPJ sintering was conducted. During APPJ-sintering, numerous NaCl crystals precipitated and their sizes (large cavity sizes after DI-water rinsing) increased with the NaCl concentration of the added solution. The dual-scale porous TiO2 was then used as the photoanode of a DSSC. With an 1-wt% NaCl solution added to the TiO2 pastes, the efficiency (photocurrent density) increased from 5.89% (11.68 mA/cm2) to 6.57% (12.75 mA/cm2). The efficiency and photocurrent density of DSSC decreased as the NaCl concentration exceeded 1 wt%. Large cavities could enhance light scattering and light trapping, thereby increasing the photocurrent (short-circuit current) and efficiency. The oversized cavity, in turn, reduced the surface area for dye-adsorption (and therefore, the dye-loading) as well as the effective photocurrent transport path, leading to the reduction in the photocurrent and efficiency.

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