Record- efficiency solar cells realised by the HyPerCells Graduate School

Lab tour of the perovskite synthesis facility at the HZB Institute for Silicon Photovoltaics, on the occasion of the HyPerCells Research Colloquium in May 2017. © HZB

The active perovskite layer was only 350 nm thick. It is embedded in organic layers made of C60 fullerene and PTAA polymer. © HZB/Uni Potsdam

Current density/voltage curve of a perovskite solar cell with an efficiency of 21.4 %. Data: Martin Stolterfoht and Christian Wolff, University of Potsdam.

The University of Potsdam and the Helmholtz-Zentrum Berlin founded the HyPerCells Graduate School just two years ago with focus on metal halide perovskites for solar applications. Now, groups involved in the graduate school have demonstrated perovskite solar cells with record-efficiencies of over 20 percent. This confirms the graduate school is at the forefront of this research in Germany and internationally highly competitive.

Metal halide perovskites are regarded as one of the most promising semiconductor materials for novel thin-film solar cells. High absorption coefficients and an optical band gap that can be chosen from a broad range make this class of materials unique. The combination in tandem solar cells of a perovskite cell with conventional semiconductor materials such as silicon enables a high-efficiency route that is especially attractive.

To concentrate research efforts in this fascinating field, the HyPerCells Graduate School was founded and jointly organised by the University of Potsdam and the Helmholtz-Zentrum Berlin two years ago. Currently, 15 doctoral students in HyPerCells from the fields of chemistry, physics, electrical engineering, and crystallography are conducting research to deepen our understanding and develop advanced materials and solar-cell designs.

Just recently, three Young Investigator Groups (YIGs) based at HZB have joined the graduate school. These close collaborations enable the students at the graduate school to understand in detail the physical and chemical processes of this rapidly developing class of materials that are essential for improving solar applications. The three important research topics of these YIGs headed by Steve Albrecht, Eva Unger, and Antonio Abate are the development of new designs for tandem solar-cell architectures, the fabrication of large-scale cells using printing technologies, and the analysis of degradation mechanisms to achieve long term stability.

And this link-up is working. In the last few months, perovskite solar cells with record efficiencies of over 20 per cent have been realised. This is the highest value for so called "inverted" perovskite solar cells with undoped contact layers. It confirms that the graduate school is at the forefront of metal halide perovskite research in Germany and also internationally highly competitive. Several important discoveries about this new photovoltaic material that have emerged from the graduate school research have been recently published in highly ranked journals such as Advanced Materials, Energy & Environmental Science, ACS Applied Materials and Interfaces, and Advanced Optical Materials. Students at the graduate school are also frequently present at national and international conferences.

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