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
- Bright prospects for tin perovskite solar cellsPerovskite solar cells are widely regarded as the next generation photovoltaic technology. However, they are not yet stable enough in the long term for widespread commercial use. One reason for this is migrating ions, which cause degradation of the semiconducting material over time. A team from HZB and the University of Potsdam has now investigated the ion density in four different, widely used perovskite compounds and discovered significant differences. Tin perovskite semiconductors produced with an alternative solvent had a particular low ion density — only one tenth that of lead perovskite semiconductors. This suggests that tin-based perovskites could be used to make solar cells that are not only really environmentally friendly but also very stable.
- Synchrotron radiation sources: toolboxes for quantum technologiesSynchrotron radiation sources generate highly brilliant light pulses, ranging from infrared to hard X-rays, which can be used to gain deep insights into complex materials. An international team has now published an overview on synchrotron methods for the further development of quantum materials and technologies in the journal Advanced Functional Materials: Using concrete examples, they show how these unique tools can help to unlock the potential of quantum technologies such as quantum computing, overcome production barriers and pave the way for future breakthroughs.
- Joint Kyiv Energy and Climate Lab goes liveHelmholtz-Zentrum Berlin and the National University of Kyiv-Mohyla Academy established on 27 November a Joint Energy and Climate Lab.