Researchers from the University of Rome Tor Vergata, Hellenic Mediterranean University, Université Grenoble Alpes (CNRS), Halocell Europe, CHOSE, ENEA, 3SUN - Enel Green Power and BeDimensional have developed a scalable four-terminal (4T) perovskite/silicon tandem architecture that combines high efficiency, semi-transparency and real-world stability by engineering a field effect junction directly inside the perovskite absorber.
a Layout of the semi-transparent 2D material-based PSMs. Each module is composed by 24 series-connected solar cells with an active area of 2.49 cm2. The total active area is 60 cm2 while the aperture area (comprising the interconnection areas) is about 63 cm2. b Demonstrator 1 (DEM1) perovskite/Si tandem panel. Each building block is composed of four parallel-connected semi-transparent perovskite modules stacked above the M2 Si-HJT bifacial cell (provided by 3SUN). c, d Pictures of the front and back side of the laminated tandem DEM1. Image from: Nature Communications
The work targets industrially relevant, large-area modules compatible with standard silicon wafer dimensions and production lines, addressing key bottlenecks in the commercialization of perovskite/Si tandems such as scalability, efficiency loss on upscaling, and outdoor durability.
Within the various tandem options, the team focuses on four-terminal 4T architectures, which allow the perovskite top and silicon bottom cells to operate at their own maximum power point, minimizing the need to modify existing Si production lines and enabling straightforward compatibility with bifacial silicon cells. However, this configuration tends to pose several challenges. First, the opaque metal electrode typically used in perovskite cells must be replaced by a semi-transparent contact in the top device, which reduces light-harvesting and removes the beneficial back-reflector effect. This is particularly critical for semi-transparent perovskite solar cells and modules, where the need to transmit light to the silicon bottom cell competes with the need for strong absorption and current generation in the perovskite. Second, when moving from small-area semi-transparent cells (ST-PSCs) to semi-transparent perovskite modules (ST-PSMs), additional series resistance, parasitic area and patterning losses tend to significantly reduce PCE. Third, most encapsulation and lamination schemes have so far been validated mainly for opaque perovskite devices, not for semi-transparent tandem-ready modules.
To overcome the voltage and recombination limitations typical of wide-bandgap perovskites used in 4T tandems, the researchers address the open-circuit voltage deficit, which stems from non-radiative recombination at deep-level acceptor defects. Ammonium salts such as phenylethyl ammonium iodide (PEAI) derivatives are known to mitigate such defects when introduced through anti-solvent engineering, but here a para-fluorinated PEAI (4-FPEAI) is used because of its higher electropositivity and stronger interaction with iodine-lead and iodine-cation antisite defects in wide-bandgap compositions. When 4-FPEAI is introduced during the anti-solvent step, it forms a surface gradient passivation (SGP) profile, with its concentration decreasing from the film surface toward the bulk. This gradient suppresses defects where they are most detrimental, near the illuminated surface, and at the same time induces a gradual p-type character and favorable energy level alignment across the perovskite layer by effectively tuning the work function.
In parallel, the group draws from previous work showing that MXenes can be used to tune the perovskite work function without degrading its optoelectronic quality. By doping the perovskite precursor with chlorine-based MXenes, they induce a local n-type character at the buried perovskite interface. Combining this buried n-type region from MXene doping with the surface-localized p-type shift from 4-FPEAI SGP creates an intentional spatial asymmetry inside a single perovskite layer. This asymmetry behaves as a field-effect junction, driven by interfacial dipoles and band bending at the perovskite interfaces, which improves carrier separation, promotes directional transport to the respective contacts and reduces non-radiative recombination. A 2D perovskite overlayer is then formed on top of the 3D perovskite, further reinforcing the p-type character at the surface and suppressing recombination at the perovskite/hole-transport-layer interface, another critical loss pathway. Importantly, this strategy avoids the need to deposit two separate perovskite layers to form a p-n homojunction, simplifying processing and making the architecture more compatible with large-area manufacturing.
Thanks to the synergy of MXene-based doping and 4-FPEAI surface gradient passivation, the team fabricated semi-transparent perovskite modules with power conversion efficiencies exceeding 16% on a 60 cm² active area. These ST-PSMs maintain good voltage and fill factor despite the absence of a reflective metal back electrode, showing that the field-effect junction and defect passivation can effectively counterbalance the optical penalty of semi-transparency. The modules are then integrated as the top devices in a four-terminal perovskite/silicon tandem panel with a total area of 0.2 m². In this configuration, the combined panel reaches a PCE of 19.45%, which is further boosted by using bifacial silicon heterojunction (Si-HJT) cells as the bottom devices. Under operating conditions with 30% ground albedo, the bifacial bottom cell harvests additional reflected light, pushing the tandem power generation density above 23 mW cm⁻².
Beyond efficiency, the study also demonstrates that this technology can withstand real-world conditions. The tandem panel was installed outdoors in Crete to evaluate its field performance, acknowledging that laboratory metrics do not always translate directly to outdoor operation. After three months of exposure, the panel retained more than 95% of its initial maximum power output, with the main observed degradation being a gradual fill factor loss of 1.27% per month when expressed as a relative decrease from the starting FF. This stability, combined with the high power generation density enabled by the bifacial Si-HJT bottom cell and the semi-transparent perovskite top module, confirms the practical viability of the approach.
The work shows that by engineering a field-effect junction through MXene-induced n-type character at the buried interface, 4-FPEAI-based surface gradient passivation and a 2D perovskite overlayer, it is possible to realize efficient, semi-transparent perovskite modules that scale to large areas and integrate seamlessly with bifacial silicon heterojunction technology. The demonstration of >16% semi-transparent perovskite modules on 60 cm², 19.45% four-terminal tandem efficiency on 0.2 m², power generation densities above 23 mW cm⁻² under 30% albedo and outdoor power retention above 95% after three months collectively underline a credible pathway toward industrial adoption of perovskite/silicon tandem panels with minimal disruption to existing silicon manufacturing.
