Organic solar technology offers many advantages when compared to more traditional types of photovoltaics, with dye sensitised solar cells (DSSCs) offering the highest conversion efficiencies of this class to date. In spite of this, the efficiencies still lag behind crystalline silicon, limiting the potential for application of this low cost technology.

The highest reported efficiencies of DSSCs have not risen dramatically in recent times. One way to overcome the stagnation is to look at tandem structures. In this system each electrode more efficiently harvests different sections of the solar spectrum.

By incorporating a photocathode and a photoanode in one device the expected increase in cost is minimal when compared to a single photoelectrode DSSC. In this case the two electrodes are in series, meaning that a high voltage can be produced when compared to a single electrode cell. Unfortunately the current density is limited by the weakest of the two electrodes.

Nickel (II) oxide has been shown to be useful as a model photocathodic system, however current densities are low, and the maximum voltage achievable is modest. A number of methods are being used to improve the performance of these devices, as well as a more in depth investigation into the photocathodic process, which is much less understood than the photoanodic one.