Highly porous TiO2 films for dye sensitized solar cells

Abstract

Highly porous nanoparticle films were investigated as alternative working electrode morphology for the synthesis of dye sensitized solar cells (DSSCs). These films were rapidly assembled by flame synthesis and direct aerosol deposition of TiO₂ nanoparticles with high specific surface area. Structural–functional analysis of their properties revealed that the film porosity is a key parameter greatly determining the resulting energy conversion efficiency (η). In fact, aerosol deposition at low substrate temperatures (∼100 °C) led to very high porosity (ε = 98%) and weak film cohesion. These films were easily resuspended upon immersion in the dye and/or electrolyte solutions resulting in very poor performances (η = 0.08%). In contrast, allowing for partial nanoparticle sintering by deposition at moderate temperatures (∼400 °C) decreased the film porosity from 98 to 95% leading to higher mechanical stability and partially preserving the large surface required for dye adsorption. As a result, these films had drastically higher current density (12.2 mA cm⁻²) and overall performances (η = 5%) representing an 8 times improvement with respect to the best reported for similar highly porous morphologies. Remarkably, their conversion efficiency decreased only slightly with increasing film thickness reaching 4.6% at 128 µm. This unique attribute suggests that high film porosity may inhibit recombination losses enabling utilization of thick films with enhanced light absorption properties.