Perovskite/Silicon Monolithic Tandem Based on a P-type High-temperature Tolerant Silicon Bottom Cell
Florent Sahli a, Gizem Nogay b, Jérémie Werner a c, Fan Fu a, Arnaud Walter b, Saeid Rafizadeh b, Vincent Paratte a, Raphäel Monnard a, Brett A. Kamino b, Peter Fiala a, Terry Chien-Jen Yang a, Matthias Bräuninger a, Ricardo A. Z. Razera a, Matthieu Despeisse b, Sylvain Nicolay b, Mathieu Boccard a, Andrea Ingenito a, Quentin Jeangros a, Christophe Ballif a b
a Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT) Photovoltaics and Thin-Film Electronics Laboratory (PV-Lab), Neuchâtel, Switzerland
b CSEM, PV-Center, Jaquet-Droz 1, 2002 Neuchâtel, Switzerland.
c ǂ now at University of Colorado Boulder, Colorado, USA.
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, Florent Sahli, presentation 164
Publication date: 11th February 2019

Increasing the power output per unit area is the most promising way to further decrease the levelized cost of electricity (LCOE) of crystalline silicon (c-Si) photovoltaics. In this regard, adding a wide-bandgap top cell to c-Si can reduce thermalization losses and enables the cell to surpass the theoretical efficiency limit of single-junctions. Organic-inorganic perovskite solar cells have been identified as promising partners for silicon solar cells due to their high power conversion efficiency at the single-junction level, sharp absorption edge, and potentially low fabrication costs. Because of these attributes, perovskite/c-Si tandems have the potential to achieve efficiencies >30% at a competitive LCOE, with a current record efficiency of 28%. Until now, all published perovskite/c-Si devices with efficiencies over 25% have featured an n-type silicon heterojunction (SHJ) bottom cell.1-4 While this type of cell can reach high efficiencies, the low thermal stability of the passivating and selective amorphous silicon layers of SHJ cells limit the perovskite top cell processing to temperatures below 250°C, which limits the choice of charge-selective contact materials. In contrast to mainstream contacting schemes, the low processing temperature of SHJs does not trigger any improvement of the wafer through impurity gettering and/or thermal donor deactivation, preventing the use of low-quality p-type wafers routinely used in the industry. Here we demonstrate the first tandem solar cell featuring a p-type bottom silicon cell based on passivating contacts formed at high temperatures,5 achieving a steady-state efficiency of 25.1%. This value is on par with our record tandems made with n-type SHJs. The c-Si bottom cell fabrication reported here is compatible with the high-temperature emitter diffusion processes used today in the c-Si PV industry. In addition, the high-temperature tolerance of the bottom silicon cell allows using charge-selective contacts formed at high temperatures such as m-TiOx, c-TiOx, NiOx, SnOx for an improved top cell efficiency.

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