Thin-film photovoltaic technology combines effectiveness and versatility

• Piling solar cells boosts their efficiency. Dealing with partners in the PERCISTAND project, scientists at the Karlsruhe Institute of Technology (KIT) have produced perovskite/CIS tandem solar cells with an efficiency of nearly 25%-- the highest value achieved so far with this technology.

In addition, this combination of products is light and versatile, making it possible to envision making use of these tandem solar cells in automobiles, portable devices, and gadgets that can be folded or rolled up. The scientists present their cause the journal ACS Energy Letters.

Perovskite solar cells have actually made astonishing progression over the past decade. Their effectiveness is now similar to that of the long-standing silicon solar cells. Perovskites are ingenious materials with a special crystal structure. Scientist worldwide are working to get perovskite photovoltaic technology ready for functional applications. The even more electrical energy they create per unit of surface, the much more eye-catching solar cells are for customers.

The effectiveness of solar cells can be enhanced by stacking two or more cells. If each of the piled solar cells is especially efficient at absorbing light from a different part of the solar spectrum, integral losses can be decreased and performance boosted. The efficiency is a measure of how much of the incident light is exchanged electricity. Thanks to their versatility, perovskite solar cells make exceptional components for such tandems. Tandem solar cells utilizing perovskites and silicon have gotten to a document efficiency degree of over 29%, substantially more than that of private cells made of perovskite (25.7%) or silicon (26.7%).

Combining perovskites with CIS for mobility and flexibility

Combining perovskites with various other materials such as copper-indium-diselenide (CIS) or copper-indium-gallium-diselenide (CIGS) promises more benefits. Such combinations will certainly make it possible to produce light and adaptable tandem solar cells that can be installed not just on buildings however additionally on lorries and mobile tools. Such solar cells could even be folded or rolled up for storage space and extended when required, as an example on blinds or awnings to offer color and generate power at the same time.

A global team of scientists headed by Dr. Marco A. Ruiz-Preciado and tenure-track teacher Ulrich W. Paetzold from the Light Technology Institute (LTI) and the Institute of Microstructure Technology (IMT) at KIT has actually been successful in generating perovskite/CIS tandem solar cells with a maximum effectiveness of 24.9% (23.5% certified). "This is the highest reported efficiency for this technology and the first high performance level got to in all with a virtually gallium-free copper-indium diselenide solar cell in a tandem," claims Ruiz-Preciado. Reducing the amount of gallium results in a narrow band gap of about one electron volt (eV), which is very close to the suitable value of 0.96 eV for the reduced solar cell in a tandem.

CIS solar cells with narrow band gap: Perovskite solar cells with low bromine content

The band gap is a material quality that identifies the part of the solar range that a solar cell can absorb to produce power. In a monolithic tandem solar cell, the band gaps have to be such that the two cells can create similar currents to attain maximum effectiveness. If the reduced cell's band gap changes, the upper cell's band gap has to be adapted to the modification, and vice versa

To adjust the band gap for efficient tandem integration, perovskites with high bromine content are typically used. However, this frequently brings about voltage declines and phase instability. Considering that the KIT researchers and their partners make use of CIS solar cells with a narrow band gap at the base of their tandems, they can produce their top cells making use of perovskites with low bromine content, which results in cells that are extra stable and effective.

"Our research study shows the capacity of perovskite/CIS tandem solar cells and develops the foundation for future development to make further renovations in their efficiency," claims Paetzold. "We've reached this landmark thanks to the exceptional cooperation in the EU's PERCISTAND project and, in particular, thanks to our close cooperation with the Netherlands Organization for Applied Scientific Research." Important groundwork was done in the CAPITANO project moneyed by Germany's Federal Ministry for Economic Affairs and Climate Action (BMWK).