Highly Catalytic Pt Nano-Particles As An Alternative to Pt Films At the Counter Electrodes of Dye Sensitized Solar Cells

Since their introduction in 1991, Dye Sensitized Solar Cells (DSSCs) have emerged as a low-cost alternative to traditional (thin film) solar cells. An important goal of current research in the area is to improve the Price/Performance Ratio. The DSSCs with the best performance use Platinum as the counter-electrode catalyst for Iodide/Tri-iodide reduction. Typically, the platinum is deposited as a thin film (~50nm for front-side illuminated DSSCs, and ~2nm for backside illuminated DSSCs).

In this work, we report an alternative that uses significantly less platinum but is able to deliver catalytic performances (efficiencies and fill factors) comparable to a 50nm thin film, and has transmittances that are better than those of 2nm Pt films.

This is achieved by depositing Platinum Nanoparticle on Fluorine-doped Tin Oxide (FTO) films in a controlled manner using RF Magnetron Sputtering at room temperature. The deposited platinum aggregates in the form of “nano-islands” on the FTO surface, with the size of the islands being primarily determined by the duration of the sputtering.

The optimum performance (photo-conversion efficiency of 4.9%) is obtained with a sputtering time of 45s. For this sputtering time,  our nano-islands are approximately 2-3 nm in diameter and have a surface density of approximately 5.9 E12 per square cm.  The amount of Platinum used is thus  ~ 400 times less than that in a 50nm Pt film, where similar photo-conversion efficiencies are obtained.  

An additional advantage of using Pt nanoparticles (as opposed to films) is that the transmittance of the layer to radiation in the UV-visible range is also greatly enhanced. Whereas Pt films typically suffer from a significant loss (absorption/reflection) of radiation (5-10% for 2nm thin films, and as much as 90% for 50 nm films), our films consisting of Pt Nano-particles on FTO show minimal changes in transmittane. This implies that our Pt-nanoparticle based counter electrodes can potentially be used in DSSCs that utilize back-side illumination as well.