Revisiting Efficiency Limits in Si-Perovskite Tandem Solar Cells—Pushing Theoretical Boundaries by Considering Radiative Efficiency and Precise Optical Modeling

The efficiency of Si-Perovskite tandem solar cells has rapidly improved over the past decade, with record performances now exceeding the previously predicted limit of 32%. In our study, we revisit these efficiency limits by incorporating new ellipsometry data to derive highly accurate optical constants, and by factoring in potential advancements in the radiative efficiency of the perovskite top cell. Previous estimations have focused on more conservative assumptions of material quality and optical losses, but with modern developments in single-junction perovskite solar cells, there is potential to push these limits further.

By systematically simulating a broad range of perovskite bandgaps and radiative efficiencies, we demonstrate that efficiencies approaching 36% are achievable if tandem sub-cells can match the performance characteristics of current high-efficiency single-junction devices. Notably, we show that if the radiative efficiency of the perovskite layer can be improved to 10%, substantial gains can be realized, and in an ideal radiative limit scenario, we predict an efficiency of up to 38%. These projections, which exceed current record efficiencies, offer a "future-proofed" maximum PCE, highlighting the critical importance of optimizing radiative efficiency and ideality factor within the tandem architecture.

Our study not only updates prior benchmarks but also introduces a comprehensive library of ellipsometry-derived optical constants that were utilized in the simulations. This dataset provides an essential resource for more accurate device modelling and enables a refined analysis of light management strategies within tandem devices.

The findings from this work underscore the potential for even further efficiency gains in Si-Perovskite tandem cells and provide a clear roadmap for the future of tandem cell research. By identifying key areas for improvement, particularly in material quality and light-trapping techniques, we lay the groundwork for the next generation of high-performance tandem solar