Preparation and characterization of TiO₂ scattering layer for plastic dye-sensitized solar cells by vacuum cold spray

Plastic dye-sensitized solar cells (DSCs) are promising photochemical solar cells owing to their light weight, flexibility of shape, and suitability for low cost roll-to-roll production. In order to improve the cell efficiency, light scattering layer was prepared on the surface of the TiO₂ nanocrystalline (NC) layer by vacuum cold spray (VCS) at room temperature using submicro-sized TiO₂ particles. The influence of the scattering layer and the connection between scattering layer and nano-TiO₂ coating was investigated to understand the improvement of the cell efficiency. For comparison, two scattering layers were prepared by a spray deposition (SD) method using an ethanol-based suspension with sub-micrometer Al ₂O₃ particles or TiO₂ particles. Results showed that all three layers presented a much higher lightreflecting capability than that of the TiO₂ nanocrystalline (NC) layer. The dark current results demonstrated that the connection between the scattering layer and the TiO ₂ NC layer of the NC+VCS-TiO₂ cell was much more effective than that of the two counterparts. As a result, the photo-induced electrons denoted by the molecules adsorbed on the particle surface in the scattering layer could successfully transport to the TiO₂ NC layer and finally to out circuit. Taking into account the efficiency increment of -13% by the light scattering effect, this good connection between the TiO₂ scattering layer and the TiO₂ NC layer contributed to an increase in efficiency by 10%, resulting in a total ∼23% efficiency improvement for the plastic DSCs using VCS-TiO₂ scattering layer. Moreover, the bending property of the NC+VCS-TiO₂ cell is much better than that of the NC+SD-TiO₂ cell and NC+SD-Al₂O₃ cell.