Hydrogenated indium oxide IO:H for semitransparent perovskite cells
Tim Helder a, Moritz Schultes a, Michael Powalla a, Erik Ahlswede a
a Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Stuttgart, Meitnerstraße, 1, Stuttgart, 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, Erik Ahlswede, 252
Publication date: 11th February 2019

Semitransparent perovskite solar cells are highly interesting not only for optically appealing stand-alone applications but especially for use as a top cell in tandem configurations in combination with low-band gap material bottom cells. Such devices have to reach highest efficiencies in combination with highest transmittance values for the near infrared (NIR) spectral region, i.e. energetically below the optical band gap to allow high current values both in the top perovskite cell and in the bottom cell. Conventionally used transparent contact layers (TCOs) as fluorine doped tin oxide (FTO) or indium tin oxide (ITO) are not optimized for such applications showing parasitic absorption in the NIR region or reduced band gaps. They have to be replaced by more suitable materials that ideally combine both very high conductivities, high transmittances across the complete relevant solar spectrum and allow a low-temperature deposition to avoid thermal stress to underlying functional layers.

Here we present an optimization study of hydrogenated indium oxide (IO:H) that could fulfil most of the mentioned prerequisites. It can be deposited at room temperature and thanks to its high mobility values even at low carrier concentrations (so that only low NIR free carrier absorption takes place) high conductivities can be reached. Hence, such layers are suitable for transparent back contacts deposited on top of temperature-sensitive perovskite layers. However, there is much more potential when the deposition is optimized by addition of hydrogen in such a way that the layers firstly grow amorphously. An additional annealing step at typically 200 °C converts the material into crystalline layers with strongly improved opto-electronical properties. Hence, such layers are especially interesting as alternative superstrate layers directly on glass, replacing the typically used commercially available FTO or ITO electrodes.

Different aspects of the optimization of semitransparent IO:H layers will be presented along with their application in complete semitransparent cell stacks, allowing absorptance values in the range of only 10 – 15 % in the NIR above 800 nm at cell efficiencies of 14.7%, much better as for the ITO or FTO references.

This work was supported by the Federal Ministry of Education and Research (BMBF) under contract number 03SF0516A (CISOVSKIT) and the federal state of Baden-Württemberg within the SOLAMO project (L75 16013)

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