In this landscape, an interconnection patent is one that makes an explicit claim on the layer or structure electrically coupling the perovskite top cell to the silicon bottom cell in a monolithic device — typically the recombination junction, tunnel junction, or interconnecting layer, or a process for optimizing that junction. Patents that describe tandem absorber materials or general device stacks without addressing this coupling layer are excluded. This distinction matters because the junction design governs current matching and optical losses between subcells, which is a separate engineering problem from the absorber chemistry itself.

The dataset shows six filings in 2021, the peak year, followed by a flat-to-declining pattern by 2022. This does not necessarily mean interest has stopped; publication typically lags the actual filing date by around 18 months, so recent years are structurally undercounted in any patent dataset. The pattern is still worth noting because it suggests the core junction architectures were claimed in a concentrated early window rather than through continuous incremental filing since.

The set is led by a cluster of French research and industrial organisations, including an industrial-gas research group that co-files repeatedly with EDF, CNRS and Institut Polytechnique de Paris, each pairing tied at five shared filings. TotalEnergies OneTech also holds a granted filing on a two-terminal tandem architecture. Rather than one company dominating, the picture is closer to a coordinated multi-partner research programme alongside a smaller number of independent corporate filings.

Filing activity concentrates in Europe and the United States, with the EPO receiving nine filings and the USPTO seven, well ahead of India, Spain and the WIPO PCT route. A practical freedom-to-operate review for a product intended for European or US markets should therefore start with EPO and USPTO family members before extending to the smaller filing offices. This concentration also means litigation or opposition risk, if it materialises, is most likely to surface in one of these two jurisdictions first.

The IPC composition shows H01L (conventional semiconductor devices) carrying 17 of the classification hits against only 6 for H10K (organic semiconductors) and 2 each for C09D (coatings) and H10F (photovoltaic-specific devices). That imbalance suggests junction claims are still mostly framed in conventional semiconductor-device language, leaving organic-electronics-specific interconnect claims and interconnecting-layer coating claims comparatively thin. A first claim written specifically around a graded tunnel-junction interlayer or a moisture-barrier interconnect coating would sit in less crowded IPC territory than a general H01L junction-structure claim.