Solar panels are, at heart, a compromise. Every photovoltaic cell is tuned to absorb light at a particular range of wavelengths. Photons above that energy threshold are partially wasted as heat; those below it pass straight through without doing anything useful. Stack two different semiconductor materials on top of each other - each optimised for a different part of the solar spectrum - and you recover much of that waste. That is the principle behind the perovskite tandem solar module, and a collaboration between Oxford PV and Germany’s Fraunhofer ISE has now reached a new milestone: 25.6% efficiency across the full area of a commercial-sized panel.
The result was presented at Intersolar Munich in June 2026 and is notable for more than the headline number. Previous efficiency records for tandem cells have mostly been set on tiny laboratory samples, where high performance is comparatively easy to achieve. Getting a large, commercially viable module to the same standard is an entirely different engineering problem.
The team built two distinct panels. The first is a 1.92-square-metre rooftop module rated at 491 W. The second is a 2.13-square-metre bifacial version, designed to capture light from both the front and rear surfaces, rated at 546 W. Both panels use a perovskite layer deposited on top of a silicon heterojunction cell. This configuration allows the perovskite to absorb high-energy blue and green photons while the silicon handles the lower-energy red and infrared light that passes through.
The efficiency gain does not come solely from semiconductor chemistry. Oxford PV and Fraunhofer ISE combined the tandem cell with a module assembly technique called Matrix Shingle, and that pairing is the real engineering story here.
In a conventional solar panel, cells are connected by soldered metal ribbons attached to busbars, the conductive strips that run across the cell surface. Those ribbons and busbars take up space. They cast shadows. They create regions of the panel that cannot generate electricity. The Matrix Shingle approach eliminates all of that. Cells are precision-cut into narrow strips and then overlapped like tiles on a roof, with each strip bonded to the next using an electrically conductive adhesive (ECA). No ribbons. No soldering. No inactive gaps.
The low-temperature ECA process is a practical advantage during manufacturing. Conventional soldering requires copper connectors and temperatures that can stress delicate perovskite layers. ECA bypasses both problems. It bonds at lower temperatures and requires no copper connectors, which simplifies the production line and reduces material costs.
There is also a subtler benefit specific to tandem cells. Because perovskite-silicon tandems operate at lower current densities than standard silicon modules - the two-layer structure means each photon contributes a higher voltage rather than a higher current - the individual strips can be cut wider than would be optimal in a single-junction shingled design. Wider strips mean fewer cuts, faster throughput, and less material lost to the cutting process. The geometry of the tandem architecture and the Matrix Shingle fit together neatly.
Stefan Glunz, head of photovoltaics research at Fraunhofer ISE, described the result as bringing together two distinct high-technology approaches developed in Europe. Oxford PV, which has been working on perovskite tandems since 2014, previously set a cell-level efficiency record of 26.9% in June 2024 and has already shipped commercial tandem modules to customers in the United States.
Ed Crossland, Oxford PV’s chief technology officer, confirmed that 25%-efficient modules are already in production, with a verified 10-year lifetime. A 26% product is planned for launch later in 2026. The company’s roadmap targets 27% by 2027 and aims to exceed 30% in subsequent years. Whether those targets are met on schedule will depend as much on manufacturing scale-up as on further materials innovation, but the trajectory is credible.
Engineering Deep Dive: How a Perovskite Tandem Solar Module Works
To understand why the perovskite tandem solar module matters, you need to understand what limits a conventional silicon solar cell - and that begins with the concept of the bandgap.
Every semiconductor has a characteristic energy level called the bandgap. When a photon strikes the material, it can only generate an electron-hole pair (and therefore an electric current) if the photon’s energy equals or exceeds this value. In silicon, the bandgap is approximately 1.1 electronvolts (eV). Photons with energy below 1.1 eV - most of the infrared spectrum - pass through the silicon without interaction. Photons with energy well above 1.1 eV do create electron-hole pairs, but the excess energy is immediately lost as heat rather than being converted to electricity. This is the fundamental reason the theoretical maximum efficiency of a single-junction silicon cell, known as the Shockley-Queisser limit, is around 33%.
A tandem cell sidesteps this limit by stacking two semiconductors with different band gaps. The top layer, made from perovskite - a crystalline material with the general formula ABX₃, where A is typically methylammonium or formamidinium, B is lead, and X is a halide such as iodide - has a bandgap tuned to around 1.6-1.7 eV. It efficiently captures high-energy blue and green photons. Photons with lower energy pass straight through to the silicon bottom cell, which has a lower 1.1 eV bandgap and captures red and near-infrared light. The result is that a much larger fraction of the solar spectrum is converted to electricity rather than lost as heat.
The theoretical efficiency limit for a two-junction tandem under standard illumination is around 46%, substantially higher than the 33% ceiling for a single junction. In practice, commercial tandems operate well below this. Still, the 25.6% achieved by the Oxford PV and Fraunhofer ISE perovskite tandem solar module already exceeds the practical ceiling of the best commercial silicon-only panels, which cluster around 22-23%.
The Matrix Shingle assembly connects to another branch of physics: current matching. In a series-connected cell, the current flowing through the circuit is limited by whichever cell produces the least current. In a standard shingled module, this means careful attention to cell-to-cell consistency. In tandem, the challenge is between the two sub-cells in each device - the perovskite layer and the silicon layer must be designed to generate equal photocurrents under real-world illumination. Engineers achieve this by tuning the perovskite composition and layer thickness.
The electrically conductive adhesive used in Matrix Shingle is typically a polymer matrix loaded with silver or other conductive particles. Curing at temperatures below 200 °C, it forms a mechanically strong and electrically conductive joint between overlapping cell strips. Compared with conventional lead-tin solder, it introduces lower thermal stress, which is particularly important for perovskite layers that can degrade at high processing temperatures.
Perovskite stability under outdoor conditions remains an active research area. Early perovskite cells degraded quickly when exposed to moisture and UV light. Oxford PV’s claim of a 10-year certified lifetime for commercially shipped modules indicates that encapsulation techniques - typically multilayer laminates combining glass, ethylene vinyl acetate, and moisture-barrier films - have advanced to the point where outdoor durability is no longer a fundamental barrier. However, long-term data over 25-year panel lifetimes are still accumulating.
For A-level physics, the perovskite tandem solar module sits at the intersection of several core topics. The photovoltaic effect, first explained by Einstein in 1905, describes how photons with energy above a threshold can eject electrons from a material - a direct application of quantum theory to a practical device. The electromagnetic spectrum determines which photons are available from sunlight and which materials can capture them. Semiconductor band theory, developed through the mid-twentieth century, provides the framework for designing materials with specific band gaps. And the engineering challenge of module assembly - precision cutting, adhesive bonding, thermal management - connects physics principles to real manufacturing constraints.
The 25.6% milestone confirms that perovskite tandem solar modules can deliver high performance at useful scales. The next test is whether Oxford PV and its manufacturing partners can produce them in volume without sacrificing the efficiency gains seen in the laboratory. If they can, the economics of solar electricity generation shift in ways that matter well beyond a single German trade fair.
- Oxford PV and Fraunhofer ISE have built a perovskite tandem solar module achieving 25.6% efficiency across its full area — a world first for this technology combination.
- The Matrix Shingle design cuts cells into strips and overlaps them like roof tiles, eliminating inactive spacing and removing the need for soldered metal busbars.
- Two modules were produced: a 491 W rooftop panel (1.92 m²) and a 546 W bifacial version (2.13 m²).
- Oxford PV’s CTO Ed Crossland says modules surpassing 26% efficiency are planned for later in 2026, with a roadmap targeting over 30%.
- The result connects directly to A-level physics topics including semiconductor bandgaps, the photovoltaic effect, and the electromagnetic spectrum.
