Nanophotonic front electrodes for perovskite-based tandem photovoltaics
Ihteaz Muhaimeen Hossain a b, Yidenekachew Donie a b, Raphael Schmager a, Mohamed S. Abdelkhalik a, Andrei Karabanov a, Somayeh Moghadamzadeh b, Jonas A. Schwenzer b, Uli Lemmer a b, Bryce S. Richards a b, Guillaume Gomard a b, Ulrich W. Paetzold a b
a Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
b Light Technology Institute, Karlsruhe Institute of Technology, Engesserstr. 13, 76131 Karlsruhe, 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, Ihteaz Muhaimeen Hossain, presentation 119
DOI: https://doi.org/10.29363/nanoge.hopv.2019.119
Publication date: 11th February 2019

The unprecedented growth of perovskite solar cells (PSCs) during the last decade made perovskite photovoltaics a competitive technology as the power conversion efficiencies (PCEs) reach staggering values close to 24%. Very recently, it was also demonstrated that in conjunction with Si in 4-terminal architecture, the tandem PCE stretched out to 28%, exceeding the PCE of single junction Si PV already today.

One prominent factor that still limits the PCE of state-of-the-art perovskite tandem PV is the imperfect transmission of the incident light below the bandgap of the perovskite top cell into the Si bottom solar cell. In order to explore this, the transmission at the front interfaces of the perovskite top solar cell must be increased. In this work, we develop polymer nanopillars embedded in an indium-doped tin oxide (ITO) layer to form front electrodes with enhanced optical transmittance. The polymer blend lithography process is used to control the morphology of the self-assembled nanopillars, prior to ITO deposition. In comparison to planar ITO, nanopillar front ITO improves the transmission over a broad wavelength range (absolute ~5%). The continuous change in the effective refractive index due to structuring allows reduction of reflection at the nanopillar/ITO and ITO/air interface and enhances the overall transmission.

Our initial findings using optical characterization on a layer stack of PSC (glass/nanopillar ITO/SnO2/Perovskite/Spiro-OMeTAD) suggest an improved transmission below the bandgap of the perovskite. This means, that fabrication of semi-transparent PSCs with these nanostructured front ITO would result in better light transmission from semi-transparent PSC for more efficient Perovskite/Si or Perovskite/CIGS tandem solar cells.

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