Solar Cells with Ferroelectric Crystal Lattice Produce 1,000 Times More Power

Researchers from Martin Luther University Halle-Wittenberg (MLU), Germany, have developed a lattice arrangement of three different layers of ferroelectric crystals that induced a powerful effect in solar cells.

The researchers believe that on integration with the ferroelectric crystal lattice, the solar cells can become thousand times more powerful. They say that combining ultra-thin layers of different materials can raise the PV effect of solar cells by a factor of 1,000. They achieved this by creating crystalline layers of barium titanate (BaTiO3), strontium titanate (SrTiO3), and calcium titanate (CaTiO3) which they alternately placed on top of one another.

Most solar cells are currently silicon-based however, their efficiency is limited. This has inspired researchers to examine new materials, such as ferroelectrics like barium titanate, a mixed oxide made of barium and titanium. However, pure barium titanate does not absorb much sunlight and consequently generates a comparatively low photocurrent.

Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field.

According to the physicist Dr. Akash Bhatnagar from MLU’s Centre for Innovation Competence SiLi-nano, Ferroelectric means that the material has spatially separated positive and negative charges, the charge separation leads to an asymmetric structure that enables electricity to be generated from light.

Studies of these researchers from MLU were published in the journal Science Advances.

Unlike silicon, ferroelectric crystals do not require a so-called pn-junction to create the PV effect, in other words, no positively and negatively doped layers. This makes it much easier to produce solar panels, explains Dr. Bhatnagar.

He explains that the important thing here is that a ferroelectric material alternated with a paraelectric material. Although the latter does not have separated charges, it can become ferroelectric under certain conditions, like low temperatures or when its chemical structure is slightly modified.

The research group observed that the PV effect is considerably enhanced if the ferroelectric layer alternates not only with one but, with two different paraelectric layers. Hence, they embedded the BaTiO3 between SrTiO3 and CaTiO, which was performed by vaporizing the crystals with a high-power laser and redepositing them on carrier substrates. This produced a material made of 500 layers, i.e. about 200 nanometres thick.

On conducting the photoelectric measurements, the new material was illuminated with laser light. The result was surprising for the researchers even, compared to pure barium titanate of a similar thickness, the current flow was up to 1,000 times stronger—and this despite the fact that the proportion of BaTiO3 as the main photoelectric component was reduced by almost two thirds.

Dr. Bhatnagar explains that the interaction between the lattice layers appears to lead to a much higher permittivity. Also, the measurements revealed that this effect is very robust: it remained nearly constant over a six-month period. Moreover, the study is still under research to know what exactly caused this extraordinary PV effect.