Researchers from Leibniz University Hannover, Karlsruhe Institute of Technology (KIT) and the Institute for Solar Energy Research Hamelin (ISFH) recently demonstrated a three-terminal (3T) perovskite - silicon tandem solar cell that tackles fundamental limitations of conventional two-terminal (2T) tandems.
Device architecture of the 3T-TSC, illustrating the double-sided textured perovskite top cell integrated with a poly-Si on oxide (POLO) interdigitated back contact (IBC) silicon bottom cell. Image credit: Advanced Science
Standard 2T designs connect both subcells in series, forcing them to operate at the same current; the lower-current subcell limits the entire device, so achieving high efficiency requires precise current matching via a carefully chosen, typically wide-bandgap perovskite. These wide-bandgap compositions are prone to instabilities under light and heat, such as phase segregation, and real-world spectral changes over the day and seasons further disturb current balance and reduce the effective energy yield. In the new work, the team introduces a 3T tandem configuration as a robust alternative that removes the strict current-matching requirement.
The researchers developed a dedicated POLO²-IBC silicon bottom cell (poly-Si on oxide interdigitated back contact) with highly optimized recombination properties, including a textured nPOLO front side, an ITO recombination layer, and refined rear nPOLO and pPOLO contacts whose recombination current densities are reduced to the fA/cm² range, yielding carrier lifetimes on par with about 26% efficient single-junction POLO cells. These high-quality silicon bottom cells, fabricated at ISFH, are then combined with perovskite top cells processed at KIT, and the compatibility with established POLO-IBC technology highlights a realistic path toward industrial scaling of the concept.
The 3T architecture decouples the perovskite and silicon currents, allowing efficient operation over a broad perovskite bandgap range from about 1.52 to 1.73 eV without needing a single “perfect” bandgap. In controlled measurements, the 3T tandem reaches 30.1% power conversion efficiency, whereas the same physical stack operated in 2T mode achieves only 24.6% because of current-mismatch losses, even though the layer stack and perovskite bandgap are identical. For 2T tandems, efficiency varies strongly with bandgap and peaks near roughly 1.7 eV; moving away from that optimum causes pronounced performance losses, while the 3T device maintains nearly constant high efficiency across the same bandgap range thanks to its additional terminal and more flexible operating point.
To assess real-world impact, the authors of this study simulated annual energy yield under realistic climate and spectral conditions. For a high-irradiance site like Phoenix, the 3T configuration delivered about 546 kWh/m² per year compared with 513 kWh/m² for the 2T version using the same materials and structure, and with a non-optimal perovskite bandgap the yield gap can widen to nearly 90 kWh/m² annually.
These results show that the 3T approach not only raises peak efficiency but also buffers the device against spectral fluctuations over days and seasons, leading to higher practical energy yield. Overall, the study demonstrates that a carefully engineered 3T perovskite - silicon tandem with an advanced POLO²-IBC silicon bottom cell can overcome key physical constraints of conventional 2T tandems, enable the use of more stable perovskite bandgaps, and significantly improve both laboratory performance and expected field energy production.
