Process Engineering and Front ITO Optimization for Improved Light Management in Perovskite Silicon Tandem Solar Cells

Özde Ş. Kabaklı^a^,^b, Leonard Tutsch^a, Jakob Kox^a^,^e, Patricia S.C. Schulze^a, Christoph Meßmer^a^,^d, Maryamsadat Heydarian^a, Alexander J. Bett^a, Martin Bivour^a, Jan Christoph Goldschmidt^a, Stefan Glunz^a^,^d, Harald Hillebrecht^c, Martin Hermle^a

^aFraunhofer Institute for Solar Energy Systems ISE, Germany, Heidenhofstraße, 2, Freiburg im Breisgau, Germany

^bDepartment of Sustainable Systems Engineering, University of Freiburg, Germany

^cInstitute of Inorganic and Analytical Chemistry, University of Freiburg,Germany

^dFreiburg Center for Interactive Materials and Bioinspired Technologies (FIT) and Laboratory for Photovoltaic Energy Conversion, University of Freiburg, DE, Germany

^ePhysics Department, University of Regensburg, Universitätsstrasse 31, Regensburg, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of 13th Conference on Hybrid and Organic Photovoltaics (HOPV21)

Online, Spain, 2021 May 24th - 28th

Organizers: Marina Freitag, Feng Gao and Sam Stranks

Poster, Özde Ş. Kabaklı, 135
Publication date: 11th May 2021

ePoster:

Tandem solar cells consist of two or more solar cells with different bandgaps working together in a device structure. The higher bandgap solar cell is placed on top of a lower bandgap solar cell so that high energy photons are used more efficiently and thermalization losses are reduced.

Perovskite solar cells are suitable candidates as the top cell for combining with silicon in a tandem structure. Perovskite silicon tandem solar cells with an optimal perovskite bandgap of ~1.65-1.7 eV ^[1,2] promises efficiencies above 30 %.

For achieving high efficiencies with monolithic perovskite silicon tandem solar cells, good current matching between the two sub-cells and high open circuit voltages (V_OC) are necessary. These can be achieved by optimizing perovskite layer properties such as crystallinity, morphology and thickness via process engineering and by good light management in the solar cell.

In this work we show that by process engineering of our well-suited perovskite FA_0.75Cs_0.25Pb(I_0.8Br_0.2)₃ with 1.69 eV bandgap and improved TCO transparency we can get closer to higher current matched J_SC within the perovskite silicon tandem configuration. In order to reach this higher current, the effect of spin coating speed and anti-solvent on the perovskite layer thickness and morphology is studied. Moreover, process parameter optimization was done on the top indium doped tin oxide (ITO) as the TCO layer.

All of the solar cells are produced via low temperature process. The perovskite top solar cells are consisted of PTAA as hole transport layer. A PFN layer is used together with PTAA for improved wetting behavior of the perovskite. A combination of C₆₀ and SnO_X is used as the electron transport layer. Two different spin coating processes for one-step wet chemical process are compared. In spin coating process 1, only one spin speed and early, fast anti-solvent dropping are used. In spin coating process 2, two subsequent spin speeds and late, drop-wise anti-solvent dropping are used. Optical improvement of the ITO layer is done via oxygen content optimization of the sputtering process. Average short circuit current density was improved up to 15% by process engineering and ITO optimization. MgF₂ anti-reflective coating is applied to the highest efficiency solar cells per group for reducing reflection losses and further improvement of the efficiencies.

References:

[1] Hörantner, M. T. & Snaith, H. J. Predicting and optimising the energy yield of perovskite-on-silicon tandem solar cells under real world conditions. Energy & Environmental Science 10, 1983–1993

[2] äger, K., Korte, L., Rech, B. & Albrecht, S. Numerical optical optimization of monolithic planar perovskite-silicon tandem solar cells with regular and inverted device architectures. Optics Express 25, A473–A482

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