The push toward renewable energy continues to drive research on solar cell technology, and innovations in this field are steadily increasing the efficiency of solar cells and lowering fabrication costs. One of the sticking points in improving the structure of solar cells has been the arrangement of the cell’s two electrodes — one on the back and one on the front of the cell. This conventional arrangement poses two problems: the wiring requirements complicate the integration of the cell into electronic circuits, and the front electrode must be both conductive and transparent, which limits the choice of materials. Udo Bach from Monash University and colleagues in Australia1 have now developed a dye-sensitized solar cell structure in which the two electrodes are integrated on the back of the cell.

Fig. 1: Schematic diagram showing the structure of a dye-sensitized solar cell with a single ‘back plane’ electrode.Image design: Inga Tegtmeier Graphic Design

Dye-sensitized solar cells, attractive for their lower fabrication costs compared to conventional silicon-based solar cells, consist of porous titania (TiO2) that is coated with a light-absorbing dye and immersed in an electrolyte solution. Bach’s research team created a ‘back plane’ electrode for their solar cell by fashioning electrodes with interdigitated fingers — one set for the positive electrode and the other for the negative electrode (Fig. 1). The electrodes were made from fluorine-doped tin oxide (FTO), and the positive electrode was coated with platinum (Pt) as a catalyst. The electrodes were then separated from the TiO2 by a layer of zirconia (ZrO2) nanoparticles.

The fabrication process relies on an inexpensive and readily scalable combination of laser ablation, electroplating and electrophoretic deposition, making the structure promising for mass production.

When illuminated from the front, the researchers’ new cell achieved a photon-to-electron conversion efficiency of up to 56% — far exceeding the 39% rate for conventional cells. The new cells also produced higher voltages due to a reduction in charge-related losses.

The researchers plan to move their technology to polymer or metal substrates, which will allow for the fabrication of flexible devices. They will also be looking at more highly conductive electrode materials. Although still in its infancy, the work already has promising applications. “Having a single-plane non-transparent contact can allow for integrating solar cells into smart cards and other printed electronics,” says Bach.