Why Single-Junction OPV Is No Longer Enough

Single-junction organic photovoltaic devices are approaching their practical efficiency ceiling: the fundamental thermodynamic problem is that a single bandgap absorber wastes sub-bandgap photons and thermalises high-energy ones simultaneously. Tandem OPV directly addresses both loss mechanisms by stacking two or more sub-cells, each optimised for a different region of the solar spectrum, and connecting them electrically in series or parallel. As single-junction OPV efficiencies approach 20% and perovskite-based tandems have demonstrated certified efficiencies exceeding 32%, the pressure to move beyond single-junction architectures has become structural rather than aspirational.

The field spans several mechanistic approaches within a single overarching goal. All-organic tandems use conjugated polymer or small-molecule donor–acceptor sub-cells separated by an interconnecting layer (ICL). Organic–inorganic hybrid tandems pair organic sub-cells with perovskite, silicon, or chalcogenide partners. Solution-processed recombination junction tandems form the ICL from materials such as TiO₂ and PEDOT:PSS. Ternary blend and near-infrared-absorbing architectures approximate tandem spectral coverage within a single active layer — a structurally simpler but efficiency-limited alternative.

According to research published by Nature and reviewed by institutions including VU Amsterdam, the OPV field has tracked a consistent upward efficiency trajectory over three decades, with bulk heterojunction polymer:fullerene combinations rising from approximately 2.5% to over 11% PCE during the 2000s alone. The emergence of non-fullerene acceptors (NFAs) in the 2010s then unlocked a further step-change in performance, enabling the near-20% single-junction efficiencies that now define the upper boundary of the current generation.

Three Decades of Innovation: From Pigment Stacks to Perovskite Hybrids

The tandem OPV innovation arc spans approximately three decades — from the first organic pigment stack patents filed in Japan in 1996 to active manufacturing IP being filed for perovskite hybrid tandems in 2025. This timeline is not a smooth progression; it contains distinct phase transitions driven by materials breakthroughs and efficiency milestones.

Foundational Phase (1996–2012)

The two Sekisui Chemical patents (JP, 1996 and 1999) are the earliest direct tandem OPV filings in this dataset. The 1996 filing describes unit cells stacked from perylene, phthalocyanine, and quinacridone colorant composite layers arranged from the transparent electrode side inward; the 1999 refinement splits the two junction compositions to minimise electrode short-circuiting. These filings establish the foundational claim space around organic pigment-based tandem junctions — and both have since lapsed, leaving that space open. Université Laval’s 2012 work on solution-processed organic tandem cells using TiO₂/PEDOT:PSS recombination contacts achieved approximately 3.3% efficiency, representing an early ICL engineering benchmark.

Performance Breakthrough Phase (2013–2019)

UCLA’s certified 10.6% polymer tandem cell (2013) marks the first double-digit efficiency in this class, using a low-bandgap polymer with spectral response extending to 900 nm in a solution-processed architecture. Kyung Hee University’s 2015 report of a 9.02% fully solution-processed polymer tandem using a diketopyrrolopyrrole-based low-bandgap material confirmed the robustness of the approach. Simultaneously, perovskite/silicon tandems began demonstrating efficiencies above 30%, setting a competitive benchmark that would reshape R&D priorities across the field.

“The first certified polymer tandem solar cell exceeding 10% power conversion efficiency — reported by UCLA in 2013 at 10.6% — anchored the commercial plausibility of organic tandem architectures and triggered a decade of accelerating investment in ICL engineering and non-fullerene acceptor design.”

Convergence and Scaling Phase (2020–2025)

From 2020 onward, the dataset shows a strong shift toward perovskite-partnered tandems targeting efficiencies above 30%, alongside organic tandem architectures validated at certified efficiencies approaching 20% for single-junction OPV (ZAE Bayern, 2020). The most recent patent in the dataset — a tandem solar cell manufacturing method from Juson Engineering Co. Ltd. (JP, 2025) — describes monolithic integration of perovskite unit cells with secondary solar cells through buffer layers, signalling that manufacturing-scale IP is actively being filed for hybrid organic-inorganic tandem configurations. Michigan State University’s 2021 “Device Performance of Emerging Photovoltaic Materials (Version 2)” report extended its scope explicitly to tandem solar cells, including light utilisation efficiency and stability energy yield metrics, indicating that standardised tandem-specific evaluation frameworks are crystallising — a prerequisite for commercial qualification.

Four Technology Clusters Defining the Field

Tandem OPV innovation is not a monolithic field — it organises into four distinct technology clusters, each with its own materials logic, efficiency ceiling, and IP profile. Understanding which cluster a given R&D programme sits in determines both the competitive landscape and the commercialisation timeline.

Cluster 1: Organic Pigment and Small-Molecule Tandem Stacks

The earliest and most narrowly defined cluster involves stacking small-molecule organic absorbers — phthalocyanine, perylene, quinacridone — into composite multi-junction configurations. The key claim is spectral division between sub-cells via complementary dye absorption. The Sekisui Chemical filings of 1996 and 1999 define this cluster’s foundational IP, both of which are now inactive. No major industrial player has re-filed in this specific sub-space within this dataset, suggesting it remains available for differentiated IP development.

Cluster 2: Polymer Tandem Cells with Solution-Processed ICLs

This cluster encompasses conjugated polymer donor:fullerene acceptor sub-cells joined by solution-processed ICLs. Critical materials include P3HT:PCBM, PCDTBT:PC[70]BM, PCPDTBT:PC[70]BM, and low-bandgap diketopyrrolopyrrole polymers. ICL engineering — achieving optical transparency, electrical conductivity, and mechanical robustness simultaneously — is the defining challenge and the primary efficiency bottleneck identified across multiple sources. UCLA’s 10.6% certified result and Kyung Hee University’s 9.02% fully solution-processed demonstration are the benchmark achievements in this cluster.

Cluster 3: Organic–Perovskite and Organic–Inorganic Hybrid Tandems

The fastest-growing cluster in terms of recent filings and publications pairs perovskite absorbers with organic sub-cells — or with silicon and CIGS — to exploit wide bandgap tunability and solution processability. Efficiency records above 32% have been demonstrated for perovskite/silicon configurations, as documented by the Helmholtz-Center Berlin review and the Center for Physical Sciences and Technology in Vilnius. All-perovskite tandems have reached certified efficiency at and beyond 25%, with thermal loss reduction and low manufacturing cost cited as structural advantages over silicon-based tandems. The Juson Engineering Co. Ltd. patent (JP, 2025) is the most recent active filing in this cluster, covering monolithic manufacturing methods for perovskite unit cells integrated with secondary sub-cells via buffer layers.

Cluster 4: Non-Fullerene Acceptors and Ternary Blend Approaches

Non-fullerene acceptors (NFAs) with tunable bandgaps and near-infrared absorption are enabling both higher-performance binary organic cells and ternary blends that approximate tandem spectral coverage within a monolithic active layer. Empa’s ternary semitransparent organic solar cells — achieving 51% average visible transmittance at 3% PCE — directly target BIPV window applications. All-polymer tandems with complementary visible-to-near-infrared absorption bands, as reported by Kyoto University’s Graduate School of Engineering (2016), extend the approach to fully polymer-based architectures. According to research standards tracked by IEEE, NFA-enabled tandem configurations represent one of the most active areas of device physics research in photovoltaics.

Application Domains: Where Tandem OPV Competes

Tandem OPV competes across five distinct application domains, each exploiting a different subset of organic photovoltaics’ distinguishing attributes — semi-transparency, bandgap tunability, flexible substrate compatibility, and solution processability. The commercial timeline differs substantially across these domains, with niche applications likely to reach market before utility-scale configurations.

Building-Integrated Photovoltaics (BIPV) and Architectural Glazing

Semi-transparent tandem OPV is a natural fit for architectural glazing, facades, and glass roofs. Empa’s ternary semitransparent OPV work achieved 51% average visible transmittance at 3% PCE, directly targeting BIPV window applications. ZAE Bayern’s 2020 material strategy review explicitly identifies colour management and transparency as key industrial figures of merit for OPV in this domain. The combination of aesthetic integration and power generation is unique to semi-transparent OPV and cannot be replicated by opaque silicon modules.

Indoor and IoT Power Harvesting

The Korea Institute of Materials Science (KIMS) identifies organic photovoltaics as particularly well-suited to indoor photovoltaic applications for Internet-of-Things (IoT) devices, owing to bandgap tunability, high absorbance coefficient under artificial lighting spectra, and compatibility with flexible substrates. Tandem architectures are relevant here for maximising efficiency under low-irradiance, spectrally narrow artificial light sources — a use case where the spectral matching advantages of multi-junction design are most pronounced relative to device area constraints.

Agrivoltaics and Greenhouse Applications

The University of Arizona demonstrated roll-to-roll printed semi-transparent OPV arrays deployed as greenhouse roof shade for hydroponic tomato production, reducing photosynthetically active radiation (PAR) transmittance by approximately 37% while generating electricity. This dual-use application domain is unique to semi-transparent OPV and is directly enabled by the spectral tunability of organic tandems and ternary blends. The combination of crop yield management and distributed electricity generation represents a compelling value proposition in arid and semi-arid agricultural regions.

Flexible and Large-Scale Demonstration

Merck Chemicals’ solar tree installation at EXPO2015 Milan demonstrated fully solution-coated, semitransparent, flexible OPV modules at 4.5% PCE at large scale using standard printing techniques. This application domain benefits from OPV’s compatibility with roll-to-roll processing on flexible substrates — a manufacturing advantage that rigid silicon panels cannot match. According to WIPO‘s tracking of flexible electronics IP, solution-processable photovoltaics represent one of the fastest-growing sub-categories within the broader flexible device patent landscape.

Utility-Scale Tandem Solar

The highest-efficiency tandem configurations — perovskite/silicon exceeding 32% certified by the European Solar Test Installation, and all-perovskite above 25% — are targeting utility-scale deployment. The Helmholtz-Center Berlin review and the Center for Physical Sciences and Technology in Vilnius both position these as the near-term commercial tandem pathway, with large-area fabrication reproducibility and long-term outdoor stability as the primary remaining barriers. No major vertically integrated PV manufacturer appears among the tandem OPV assignees in this dataset, consistent with the technology’s pre-commercial stage.

IP Landscape and Geographic Shifts

The tandem OPV IP landscape is characterised by distributed academic and semi-industrial ownership rather than concentration in large industrial players — a pattern consistent with a technology at the pre-commercial stage. Understanding the geographic distribution of filings and the status of key assignees is essential for identifying white-space opportunities and competitive threats.

Japan dominates the earliest tandem OPV patent filings in this dataset, with both Sekisui Chemical Co. Ltd. filings from 1996 and 1999 now inactive. The United States accounts for the largest share of literature contributions, including the UCLA 10.6% polymer tandem breakthrough, the Caltech in situ recombination junction work for perovskite/silicon tandems, and Michigan State University’s performance benchmarking framework. Korea contributes multiple filings across hybrid solar cell architectures, and the most recent active tandem-specific patent in the dataset is from Juson Engineering Co. Ltd. — a Korean-origin company filing in Japan in 2025.

Chinese academic engagement is evident in the literature — Shanghai Jiao Tong University’s 2021 comprehensive review of organic tandem architectures and Fuzhou University’s 2017 multiscale simulation work both signal active research programmes. However, Chinese industrial IP filing in tandem OPV appears underrepresented in this dataset, suggesting that Chinese industrial activity may be accelerating beyond what these results capture. According to EPO patent trend data, Chinese applicants have become the largest single filer group in clean energy technologies broadly, making this a significant monitoring priority for competitive intelligence teams.

Broader OPV-adjacent assignees in this dataset — ZAE Bayern, Empa, Fraunhofer ISE, VU Amsterdam, UNIST, University of Arizona, and Korea Institute of Materials Science — form a geographically distributed academic and semi-industrial cluster concentrated in Europe, East Asia, and North America. No major vertically integrated PV manufacturer (such as First Solar, LONGi, or Jinko) appears among the tandem OPV assignees in these results, consistent with the technology’s pre-commercial stage and the absence of dominant industrial IP concentration.

Strategic Implications for R&D and IP Teams

Five strategic implications emerge directly from the patent and literature signals in this dataset — each with actionable consequences for R&D investment prioritisation, IP filing strategy, and competitive monitoring.

The Foundational Tandem OPV Patent Space Is Open

The earliest organic tandem cell patents (Sekisui Chemical, JP, 1996–1999) have lapsed, and no dominant industrial IP holder controls core tandem OPV architecture in this dataset. This creates a relatively open landscape for new entrants to build differentiated IP around ICL materials, NFA sub-cell combinations, and solution-processed manufacturing processes. Organisations with active R&D programmes in these areas should consider accelerating filing timelines before the convergence of perovskite and organic tandem architectures attracts larger industrial players.

Perovskite/Organic Hybrid Tandems: Highest Efficiency, Unresolved Barriers

Stability under outdoor conditions and large-area fabrication reproducibility are the critical unresolved challenges identified across multiple sources in this dataset. R&D investment should be weighted toward encapsulation, defect passivation, and scalable deposition methods. The Juson Engineering Co. Ltd. 2025 patent on monolithic perovskite tandem manufacturing methods signals that manufacturing-process IP is already being filed, making process innovation a priority claim area.

Application-Specific Tandem OPV May Commercialise First

The semi-transparency, bandgap tunability, and flexible substrate compatibility of organic tandems create niche but growing markets — indoor IoT, BIPV, agrivoltaics — where silicon-based tandems cannot compete directly. IP strategies focused on these verticals may encounter less crowded claim space than utility-scale configurations. The University of Arizona’s greenhouse demonstration and KIMS’s IoT power harvesting work both represent proof-of-concept validations of commercially distinct value propositions.

ICL Engineering Remains the Critical Differentiator

Multiple sources identify the recombination/interconnecting layer as the primary efficiency bottleneck in all-organic tandems. Materials innovations at this layer — particularly in optical transparency, charge selectivity, and process compatibility — are likely to generate high-value, defensible IP. The solution-processed TiO₂/PEDOT:PSS approach demonstrated by Université Laval in 2012 remains a reference architecture, but significant performance headroom exists for novel ICL material combinations.

East Asian IP Activity Is the Key Monitoring Priority

While the earliest tandem OPV filings are Japanese and key academic contributions come from Europe and North America, the most recent active patent in this dataset is from a Korean-origin company filing in Japan. Chinese academic engagement is evident and accelerating. Competitive intelligence teams should monitor Chinese and Korean patent filings in tandem OPV sub-classes — particularly ICL materials, NFA-based sub-cells, and perovskite manufacturing processes — as the most likely source of near-term IP concentration risk.