The photovoltaic effect increases in solar cells with three crystal layers

The photovoltaic effect of ferroelectric crystals in solar cells can be increased by a factor of 1,000 if three different materials are arranged in a lattice, according to a study by researchers at German Martin Luther University Halle-Wittenberg (MLU). They created crystalline layers of barium titanate, strontium titanate and calcium titanate, which they alternately superimposed. The results, which could contribute to a significantly higher efficiency of solar modules, were published in the journal Science Advances.
Currently, most solar cells are based on silicon, but their efficiency is limited. For several years, therefore, research has been conducted on new materials, such as ferroelectrics, like barium titanate, a mixed oxide of barium and titanium. »Ferroelectric means that the material has spatially separated positive and negative charges,« explains physicist Akash Bhatnagar from MLU's SiLi-nano Center for Innovation Competence. Unlike silicon, ferroelectric crystals did not require a so-called pn junction, i.e. positively and negatively doped layers, for the photovoltaic effect, which made the production of solar modules much easier, he said. Research has shown that combining different materials in extremely thin layers significantly increases the yield of solar energy. »The important thing here is to alternate a ferroelectric material with a paraelectric material. Although the latter does not have separate charges, it can become ferroelectric under certain conditions, such as low temperature or slight modifications to the chemical structure,« Bhatnagar says. Bhatnagar's research group has now found that the photovoltaic effect is again significantly enhanced when the ferroelectric layer alternates not just with one, but with two different paraelectric layers.
For the photoelectric measurements, the new material was irradiated with laser light. The result: compared to pure barium titanate of similar thickness, the current flow was up to 1,000 times stronger. The effect was almost constant over a period of six months, the scientists said.
The study was supported by the German Federal Ministry of Education and Research (BMBF), the German Research Foundation and with funding from the European Regional Development Fund (ERDF).

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