Fully Textured Monolithic Perovskite/Silicon Tandem Solar Cells Realized by Co-Evaporation
Marcel Roß a, Stefanie Severin a, Amran Al-Ashouri a, Eike Köhnen a, Philipp Tockhorn a, Philipp Wagner a, Jona Kurpiers a, Bernd Stannowski a, Steve Albrecht a
a Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, 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, Marcel Roß, presentation 103
DOI: https://doi.org/10.29363/nanoge.hopv.2022.103
Publication date: 20th April 2022

Monolithic tandem solar cells that pair silicon with metal halide perovskite have recently achieved power conversion efficiencies (PCE) above 29%.[1] Typically, such perovskite/silicon tandem solar cells (PSTSCs) are realized with solution processed perovskite absorber layers. However, solution based deposition involves a number of limitations. In particular, the conformal coverage of textured surfaces or composition gradients in the absorber material can only be realized with considerable effort. These limitations can be overcome by co-evaporating the perovskite precursor materials. In addition, the co-evaporation process offers a good control over layer thickness and can be easily scaled to large areas.

In this work, different lead halide perovskite compositions are prepared by co-evaporation and integrated as top absorber material into monolithic PSTSCs. By combining front side polished silicon heterojunction bottom cells with co-evaporated methylammonium lead iodide (MAPbI3), planar PSTSCs with PCE above 26% are realized. However, the integration of co-evaporated MAPbI3 into fully textured monolithic PSTSCs was not possible. Through an optical and morphological analysis we demonstrate that co-evaporated MAPbI3 on textured glass and silicon surfaces is degraded by subsequent atomic layer deposition (ALD) of tin oxide, a typical buffer layer for highly efficient PSTSCs.[1,2] To realize fully textured monolithic PSTSCs with co-evaporated perovskite, we replaced MAPbI3 with a chemically more stable formamidinium based perovskite composition. A conformal coverage of the pyramid texture minimizes reflection losses compared to front side planar PSTSC to only 1.62 mA/cm2 in the wavelength range 300 to 1200 nm, and the tandem cells reach an efficiency of up to 24.6%.[3] Moreover, we prepared a large area proof of concept PSTSC with a size of 61 cm2 (designated illumination area) to demonstrate that the herein used co-evaporation process is suitable to be adapted on larger areas.

Our results demonstrate that the co-evaporation technique can enable fully textured tandem solar cells and indicate that stability against degradation during processing is one core criterion for the development of co-evaporated perovskite compositions for PSTSCs.

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