Highlight in EPJ Photovoltaics: An attractive pathway towards high efficiency tandem

The Editors-in-Chief of EPJ Photovoltaics, Pere Roca i Cabarrocas and Jean-Louis Lazzari, are pleased to highlight an important paper published recently in the Special Issue on ‘EU PVSEC 2023: State of the Art and Developments in Photovoltaics’.

The article “Monolithic 3-terminal perovskite/silicon HBT-based tandem compatible with both-side contact silicon cells: a theoretical study” by researchers from Politecnico di Torino dives into the concept of using the bipolar transistor architecture to realize perovskite-on-silicon tandem solar cells with three terminals.

Multi-terminal architectures are appealing for tandem technologies in hybrid material systems because they loosen energy gap matching constraints and are expected to provide a higher energy yield than the two-terminal counterpart.

The bipolar transistor approach studied in this paper would make it possible to develop a three-terminal monolithic tandem with a very simple structure made of a perovskite solar cell directly deposited on top of very common commercial silicon cells. This approach would remove the need for tunnel junctions or recombination layers, and for interdigitated-back-contact silicon cells, hence simplifying fabrication.

The researchers discuss the physics of the bipolar-transistor-tandem with the aid of simulations and show its ability to maximize the power conversion efficiency thanks to the independent operation of the sub-cells. In addition, they study possible layouts for the current collecting grids and explore the potential of their approach in the perspective of large area tandem cells. The results suggest that the bipolar transistor can offer an attractive pathway towards high efficiency tandems with mismatched perovskite/silicon cells and provide possible directions for future research on materials and device engineering of this architecture.