Highly Efficient Monolithic Perovskite Silicon Tandem Solar Cells: Analysing Current-Mismatch Conditions
Eike Köhnen a, Marko Jošt a, Anna Belen Morales-Vilches b, Philipp Tockhorn a, Amran Al-Ashouri a, Bart Macco a, Lukas Kegelmann a, Lars Korte a, Bernd Stannowski b, Bernd Rech a, Rutger Schlatmann b, Steve Albrecht a
a Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Si-Photovoltaik
b Helmholtz-Zentrum Berlin für Materialien und Energie GmbH PVcomB, Schwarzschildstraße 3, Berlin, 12489, Germany
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Eike Köhnen, 079
Publication date: 11th February 2019

Metal halide perovskites have shown great promise to enable highly efficient and low cost tandem solar cells when being combined with silicon. Here, we combine rear emitter silicon heterojunction bottom cells with p-i-n perovskite top cells into highly efficient monolithic tandem solar cells. By optimizing the transparent n-type front contact layer stack, a certified power conversion efficiency (PCE) of 25.0% is achieved at highly unmatched short circuit current densities of the sub-cells. Further improvements of the silicon bottom cell, the top contact and perovskite thickness allowed to increase the JSC above 19.5 mA cm-2, enabling a remarkable tandem PCE of 26.0%, however with a slightly limited fill factor (FF). To test the FF dependency as function of sub-cell mismatch, various illumination spectra are utilized by using a LED based sun simulator. This illumination-variation is also relevant for outdoor applications with the sun spectrum changing over the day and thus highly important for energy yield analysis, especially when comparing 4- and 2-terminal architectures. Interestingly, the unmatched currents improve the FF of the tandem solar cell and thus the loss in tandem PCE due to lower JSC at unmatched conditions is less pronounced. The finding is confirmed by electrical simulations based on input parameters from reference single junction devices. The simulation shows that, especially the FF is not at its full potential in the experiment and reveals an even higher potential of the tandem design.

The authors acknowledge funding from HyPerCell (Hybrid Perovskite Solar Cells, www.perovskites.de) joint Graduate School, as well as from the German Federal Ministry for Economic Affairs and Energy (BMWi) through the “PersiST” project (grant no. 0324037C). Further funding was provided by the Federal Ministry of Education and Research (BMBF) for funding of the Young Investigator Group Perovskite Tandem Solar Cells within the program “Materialforschung für die Energiewende” (grant no. 03SF0540) and by the Helmholtz Foundation within the HySPRINT Innovation lab project.

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