Maximum efficiency, minimum materials and complexity
The a-Si:H is deposited on a AZO-film that acts as a transparent front contact. A ITO-layer serves as rear contact. The organic sub-cell possesses a front contact made of a conductive polymer material (PEDOT) and a metallic rear contact. © Uni Potsdam
Silicon-based thin-film solar cell with a supplementary organic layer can utilise infrared light as well
The cell consists of many active layers, which taken together are less than one micron thick. The new hybrid solar cell is constructed of two extremely thin layers of amorphous silicon as well as an organic layer. Despite the low volume of materials employed, the hybrid cell attains recording-breaking efficiency of 11.7%.
The organic layer is made of fullerenes, also known as “soccer ball molecules”, mixed with semiconducting polymers. It is able to convert infrared light that cannot be utilised by the silicon layers into electrical energy.
The complementary compound of organic and inorganic materials in a stacked cell offers a promising option for future solar cells. The cell was jointly developed through the BMBF “Leading-edge Research and Innovation in the New German Länder” programme by teams at the University of Potsdam and HZB who have published their work in the renowned technical journal Advanced Materials.
The fundamental component of the cell is a very thin layer of amorphous silicon interspersed with hydrogen (hydrogenated amorphous silicon / a-Si:H). These kinds of simple thin-film solar cells do not attain high efficiencies, as they can only use photons in the blue and green regions of the spectrum.
Steffen Roland, a doctoral student in Prof. Dieter Neher’s group at the University of Potsdam, and Sebastian Neubert, a doctoral student under Prof. Rutger Schlatmann in PVcomB at HZB, added first another a-Si:H layer to a tandem cell and then deposited an additional organic layer that enables infrared light as well to be converted into electrical energy. In this manner, they were able to increase the efficiency of the triple-junction cell to over 11%. At the same time, the structure of this solar cell is able to withstand the effects of aging better. This success impressively demonstrates how the close cooperation of doctoral students from different fields of study (organic semiconductors and inorganic semiconductors) leads to new device structures with improved properties.
“The cell can be fabricated easily with established thin-film technology common in the industry, and is also suited to production in large sheets”, explains Schlatmann. Neher adds: “The high absorption coefficients of a-SI:H layers and the properties of the organic layer make possible an active stack no thicker than one micron - that is maximum efficiency with minimum materials!”
Article first published online 7 January 2015 in Advanced Materials: Hybrid Organic/Inorganic Thin-Film Multijunction Solar Cells Exceeding 11% Power Conversion Efficiency
DOI: 10.1002/adma.201404698
- Key technology for a future without fossil fuelsIn June and July 2025, catalyst researcher Nico Fischer spent some time at HZB. It was his sabbatical, he was relieved of his duties as Director of the Catalysis Institute in Cape Town for several months and was able to focus on research only. His institute is collaborating with HZB on two projects that aim to develop environmentally friendly alternatives using innovative catalyst technologies. The questions were asked by Antonia Rötger, HZB.
- 5000th patient treated with protons for eye tumoursFor more than 20 years, Charité – Universitätsmedizin Berlin and the Helmholtz-Zentrum Berlin (HZB) have been jointly offering proton radiation therapy for eye tumours. The HZB operates a proton accelerator in Berlin-Wannsee for this purpose, while Charité provides medical care for the patients. The 5000th patient was treated at the beginning of August.
- Iridium-free catalysts for acid water electrolysis investigatedHydrogen will play an important role, both as a fuel and as a raw material for industry. However, in order to produce relevant quantities of hydrogen, water electrolysis must become feasible on a multi-gigawatt scale. One bottleneck is the catalysts required, with iridium in particular being an extremely rare element. An international collaboration has therefore investigated iridium-free catalysts for acidic water electrolysis based on the element cobalt. Through investigations with various methods, among them experiments at the LiXEdrom at the BESSY II X-ray source in Berlin, they were able to elucidate processes that take place during water electrolysis in a cobalt-iron-lead oxide material as the anode. The study is published in Nature Energy.