A two-terminal (2T) tandem cell is fabricated as a monolithic stack in which the top and bottom sub-cells share a single pair of external contacts, connected in series through an internal recombination or tunnel junction layer. Patent claims for 2T devices typically focus on that internal junction, the contact architecture, and the deposition sequence that bonds the two sub-cells. A four-terminal (4T) tandem cell keeps the sub-cells electrically independent, each with its own contacts, so claims more often target optical coupling structures, transparent conductive layers, spectral splitting elements, and independent maximum-power-point tracking circuitry. The distinction matters for freedom-to-operate analysis because a team developing a 4T mechanically stacked module will encounter a different — and in some sub-areas thinner — body of prior art than one working on 2T monolithic integration.

Within the searched corpus, the United States (37 records) and European Patent Office (21 records) account for the largest share of protection, together representing close to 70% of the mapped families. PCT filings (10 records) provide some multilateral coverage, and India and South Korea have modest national-phase representation. Australia has a single record. This geographic concentration means that freedom-to-operate risk is highest for products commercialised in the US and EU; conversely, manufacturers targeting Southeast Asian and South Asian markets may encounter less direct patent exposure from this specific body of prior art, though national filings outside this corpus could still apply.

On the evidence available, the filing peak for this specific corpus occurred in 2018 at 15 families, with a marked decline by the 2022 midpoint to 4 families. Publication typically lags filing by roughly 18 months, which means the most recent cohort in the data is understated — but even accounting for that lag, the trend is flat rather than growing. This pattern is consistent with a technology where foundational architectural claims were filed during the 2015–2020 research build-up, and where new entrants are now more likely to pursue narrow process or materials positions than broad structural claims. Teams considering new filings should treat the post-peak plateau as a signal to focus on differentiated sub-areas rather than attempting to re-stake occupied ground.

The most-cited family in the corpus — the heterojunction V-groove multijunction device — has accumulated 155 citations, a figure more than four times greater than the next cluster. In a compact 82-family corpus, citation counts within the dataset favour older records simply because more subsequent filers have had the opportunity to reference them; they are a measure of technical influence on the field's drafting vocabulary, not of current commercial importance. The V-groove heterojunction record's dominance suggests that geometric and materials innovations from earlier multijunction photovoltaic research have set the structural reference frame for both 2T and 4T claims filed since. Anyone drafting new claims should analyse this family carefully to understand which features are now prior art and which remain open for differentiation.

The corpus shows a pattern typical of early-stage advanced energy technology: a small cluster of well-resourced assignees at the top of the ranking — including a major consumer electronics manufacturer and a French public-private research consortium — and a long tail of single-family filers including universities, national labs, and start-ups. The French consortium (linking an industrial-gas group, a national utility, a public research agency, and an engineering school) has co-filed across multiple families, creating complex joint-ownership arrangements that may affect licensing flexibility. LG Electronics, the assignee of the representative EP3270432A1 record, divested its solar business in 2022, meaning that portfolio ownership and licensing stance should be independently verified before assuming continuity. For the tail of single-family academic filers, technology transfer offices are often the appropriate licensing contact.

Several technically specific sub-areas show comparatively thin claim coverage relative to their commercial importance. Four-terminal optical coupling layers — the structures that manage light transmission from top to bottom sub-cell in mechanically stacked devices — appear underrepresented, as do perovskite bandgap grading strategies tuned specifically for 4T configurations. On the 2T side, recombination junction passivation using novel interfacial materials is an emerging research area where patent vocabulary is not yet standardised, which can create first-mover advantages for careful drafters. System-level claims covering module-integrated maximum-power-point tracking for 4T arrays, flexible-substrate encapsulation, and spectral tuning for indoor or diffuse-light applications also have limited representation in this corpus. White space identified through landscape analysis should always be validated against the full prior-art record, including non-patent literature, before a filing programme is launched.

The Air Liquide–EDF–CNRS–École Polytechnique grouping has co-filed across multiple families, with five documented co-assignee pairs in the corpus, making it the most structurally coordinated multi-institution presence in the dataset. Consortium filings of this type typically originate in publicly funded research programmes and tend to produce broad method and device claims reflecting fundamental research insights rather than narrow manufacturing optimisations. For competitors, this means two practical risks: the claims may cover process steps that are difficult to avoid, and the multi-party ownership structure can slow licensing negotiations because all co-owners must agree on terms. Entities working in thin-film deposition processes relevant to tandem junctions should map their workflows against these families as an early step in their freedom-to-operate assessment.

EP3270432A1 describes a monolithic perovskite-on-silicon tandem cell with a nano-electrode structure patterned on the front transparent electrode, designed to extend the optical path of incident light. The claims extend from the cell level to module-level interconnection, meaning the family potentially creates exposure across both the device and the integrated product. The nano-electrode feature is the most structurally distinctive element: teams working on front-contact transparency in perovskite-silicon stacks will need to assess whether their specific electrode geometry falls within the claim scope. Given that LG Electronics exited its solar business, the current owner of this patent family and their enforcement posture should be confirmed independently — portfolio transfers in divested business units sometimes result in assertions by entities with different commercial incentives.