New records in perovskite-silicon tandem solar cells through improved light management



New records in perovskite-silicon tandem solar cells through improved light management

The SEM image shows the cross-section of a silicon perovskite tandem solar cell. Credit: HZB

Using microstructured layers, an HZB team has succeeded in increasing the efficiency of perovskite-silicon tandem solar cells, accounting for 25.5 percent, the highest published value to date. The team used computational simulations to investigate light conversion in different device designs with different nanostructured surfaces. This enabled optimization of light management and detailed analysis of energy yields. The research is now published in Energy and environmental science.

Tandem solar cells made of silicon and metal halide perovskite compounds can convert a particularly large part of the solar spectrum into electrical energy. However, part of the light is reflected and thus lost for energy conversion purposes. With the aid of nanostructures the reflection can be significantly reduced, so that the solar cell receives more light. For example, pyramid-shaped microfigurations can be etched into silicon. These characteristics, however, cause microscopic roughness in the silicon surface, making it no longer suitable as a substrate for the deposition of extremely thin perovskite layers. This is because perovskites are normally deposited on a polished wafer using solution processing to form an extremely thin film, much thinner than the pyramidal features. A roughly etched silicon surface layer therefore prevents the formation of a uniform conformal layer.

The efficiency improved from 23.4 percent to 25.5 percent

A team led by HZB physicist Steve Albrecht investigated an alternative approach to light management with textures in tandem solar cells. The team manufactured an efficient perovskite / silicon tandem device whose silicon layer was etched at the back. The perovskite layer can be applied by spin coating on the smooth front of the silicon. The team then applied a polymer light management foil (LM) to the front of the device. This allowed a high-quality perovskite film to be processed on a flat surface, while the texture at the front was still used. "In this way, we succeeded in significantly improving the efficiency of a monolithic perovskite-silicon heterojunction tandem cell from 23.4 percent to 25.5 percent," says Marko Jošt, first author of the study and postdoc in Albrecht & # 39; s team.

New records in perovskite-silicon tandem solar cells through improved light management

Above the perovskite layer, a structured polymer film provides better light absorption. Credit: HZB

Numerical model shows possibility for a maximum of 32.5 percent

In addition, Jošt and colleagues have developed an advanced numerical model for complex 3D functions and their interaction with light. This allowed the team to calculate how different device designs with textures on different interfaces affect efficiency. "Based on these complex simulations and empirical data, we believe that an efficiency of 32.5 percent can be achieved realistically – if we succeed in integrating high-quality perovskites with a band gap of 1.66 eV", says Jošt.

Suitable for building integrated PV

And team leader Steve Albrecht adds: "Based on real weather data, we were able to calculate the energy yield over the course of a year for the various cell designs and for three different locations." In addition, the simulations show that the LM film on the front of the solar cell device is particularly advantageous under diffuse light irradiation, i.e. not only under light incident perpendicularly. Tandem solar cells with the new LM-foil could therefore also be suitable for inclusion in building-integrated photovoltaic solar energy (BIPV), which opens up huge new areas for energy generation from large skyscraper facades.


Perovskite / CIGS tandem cell with a record efficiency of 24.6 percent


More information:
Marko Jošt et al, Textured interfaces in monolithic perovskite / silicon tandem solar cells: advanced light management for improved efficiency and energy yield, Energy and environmental science (2018). DOI: 10.1039 / C8EE02469C

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