Monolithic 2-Terminal Perovskite Silicon Tandem Solar Cells
Patricia S. C. Schulze a, Özde Ş. Kabaklı a, Minasadat Heydarian a b, Oussama Er-Raji a b, Maryamsadat Heydarian a, Raphael Efinger a, Oliver Schultz-Wittmann a, Christoph Messmer a b, Alexander J. Bett a, Oliver Fischer a b, Leonard Tutsch a, Denis Erath a, Sebastian Pingel a, Thibaud Hatt a, Martin Bivour a, Jan Christoph Goldschmidt a c, Martin Hermle a, Stefan W. Glunz a b
a Fraunhofer Institute for Solar Energy Systems ISE, 79110 Freiburg, Germany
b University of Freiburg, Germany, 79110 Freiburg, Germany
c University of Marburg, Germany, 35037 Marburg, Germany
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Oral, Patricia S. C. Schulze, presentation 183
Publication date: 20th April 2022

To enable terawatt-scale photovoltaics, resource and cost efficiency are mandatory. Perovskite silicon tandem solar cells can achieve both goals by exceeding the efficiency limit of 29.4% of single junction silicon solar cells [1], with only little additional production costs [2]. We aim for monolithic 2-terminal tandem devices to facilitate module integration and to avoid parasitic absorption in laterally conductive layers.

Starting from a p-i-n perovskite top solar cell with a 1.68 eV absorber on p-type heterojunction silicon bottom solar cells with a pyramidal rear side texture and a planar front [3], we elaborate optimization steps to maximize the photocurrents in the sub-cells and achieve current matching. Supported by optical simulation using transfer matrix formalism [4,5], main process adaptions are addressed, e.g. development of a more transparent front contact layer and fine-tuning the perovskite band gap. Spectral metric analysis [6] – comprising a systematic variation of the illumination spectrum, while keeping the overall irradiance constant – is applied to access the individual sub-cell´s current generation and confirm current matching. A certified current density of 19.6 mA/cm2 is achieved for optimized tandem devices with planar front. For further current increase and higher energy yield [7], fully textured tandem devices are needed. For this purpose, we investigate the dry/wet hybrid (evaporation and wet processing) route to allow perovskite deposition with tuneable band gap on µm-sized silicon texture.

Concerning the tandem´s voltage, we investigate different charge transport materials and interface passivation. Electrical simulation of our full tandem stack in Sentaurus TCAD gives insight into the tandem´s band diagram and charge carrier extraction and serves as basis for further device optimization.

Regarding metallization and up-scaling, low-temperature silver paste screen printing is investigated for front metallization of the tandem device. Considering high costs of silver, electroplated copper contacts are considered as an alternative and demonstrated on semi‑transparent perovskite solar cells as a proof-of-concept [8].

This work was partially supported by the Fraunhofer Lighthouse Project MaNiTU and the German Federal Ministry for Economic Affairs and Energy (BMWi) under contract number 03EE1086A (prEsto) and 03EE1087A (KATANA).

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