Thin Conformal Hole Transport Layers Enabling Highly Efficient Monolithic Perovskite/CIGSe Tandem Solar Cells
Marko Jost a, Tobias Bertram b, Dibyashree Koushik c, Jose A. Marquez d, Marcel A. Verheijen c, Eike Köhnen a, Amran Al-Ashouri a, Thomas Unold d, Mariadriana Creatore c, Iver Lauermann b, Christian A. Kaufmann b, Rutger Schlatmann b, Steve Albrecht a
a Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin, Berlin, Germany
b Helmholtz-Zentrum Berlin, PVcomB, Berlin, Germany
c Department of Applied Physics, Eindhoven University of Technology (TU/e), the Netherlands
d Department Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin, Berlin, 14109, 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
Oral, Marko Jost, presentation 136
DOI: https://doi.org/10.29363/nanoge.hopv.2019.136
Publication date: 11th February 2019

Perovskite solar cells have lately established themselves as one of the best choices for a top cell in a monolithic tandem devices. As a bottom cell, silicon has mostly been the material of choice. Besides its high efficiency, one of the main reasons is the possibility of polishing its front side. This way wet chemical processing of very thin contact layers (<20 nm) and perovskite, to day still the most efficient way of fabricating perovskite solar cells, is feasible. On the other hand, copper indium gallium diselenide (CIGSe) solar cells were only rarely used as bottom cells due to their rough surface, with their root-mean-square roughness (σRMS) typically in the range between 50-200 nm. Here, we present highly efficient monolithic perovskite/CIGS solar cells, enabled by a conformal deposition of NiOx via atomic layer deposition (ALD) [1]. A 10 nm thick layer of NiOx is already capable of preventing shunting of the top cell. This way a PCE of 18% was measured. However, NiOx/perovskite suffers from strong recombination and consequently low VOC. By introducing an additional layer of the polymer PTAA we optimize the limiting NiOx/perovskite interface. Thus, a p-type selective contact bilayer is introduced, leading to a monolithic perovskite/CIGSe tandem device with a stabilized PCE of 21.6% in maximum power point tracking over 10 minutes. TEM and EDX measurements are carried out, confirming the conformal growth of the ALD NiOx and non‑conformal growth of spin-coated PTAA. To investigate the absorber quality of both subcells we measure absolute photoluminescence (PL) [2] on the fabricated tandem device. Calculated quasi-Fermi level splitting of the subcells match well with the VOC of the reference single‑junction devices. This indicates that lower VOC of the tandem solar cell could be improved by tailoring recombination layers between the two subcells. Our results show a way for exploiting great potential of perovskite/CIGSe.

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