Perovskite–Silicon Tandem Solar Cells: How Researchers Are Breaking the 35% Efficiency Barrier

Conventional silicon solar cells have transformed the photovoltaic industry, but their efficiency is fundamentally constrained by the physics of single-junction devices. Perovskite–silicon tandem solar cells offer a different approach: instead of asking one absorber to capture the entire solar spectrum, they combine two photovoltaic materials with complementary bandgaps.

This architecture has rapidly become one of the most important directions in next-generation photovoltaics. By 2026, independently confirmed perovskite–silicon tandem efficiencies had moved beyond 35% at the research-cell level, while researchers were increasingly focusing on the harder problems of stability, large-area fabrication, interfaces, and commercialization.

But how do tandem solar cells actually achieve these high efficiencies, and what prevents them from immediately replacing conventional silicon photovoltaics?

Why Combine Perovskite with Silicon?

A conventional silicon solar cell uses a single absorber with a bandgap of about 1.12 eV. This is highly effective, but a single-junction solar cell cannot efficiently use every part of the solar spectrum.

High-energy photons can lose excess energy as heat after absorption, while lower-energy photons may pass through the absorber without generating useful current.

A tandem architecture addresses this problem by stacking absorbers with different bandgaps.

In a typical perovskite–silicon tandem solar cell, the wider-bandgap perovskite acts as the top cell while crystalline silicon forms the bottom cell.

The perovskite absorbs a large fraction of the higher-energy visible photons. Lower-energy near-infrared photons can then reach the silicon subcell.

This spectral splitting reduces some of the fundamental losses associated with single-junction photovoltaics.

Perovskite top cell + silicon bottom cell → broader solar-spectrum utilization → higher theoretical efficiency potential.

The engineering challenge, however, is considerably more complicated.

How Does a Perovskite–Silicon Tandem Solar Cell Work?

The most widely studied architecture is a two-terminal (2T) monolithic tandem.

In this configuration, the perovskite top cell and silicon bottom cell are electrically connected in series. The device must therefore satisfy several conditions simultaneously:

• The perovskite must absorb the appropriate portion of sunlight.
• The silicon bottom cell must receive sufficient transmitted light.
• The currents generated by the two subcells must be properly matched.
• Charge carriers must cross the recombination or interconnection layer efficiently.
• Optical losses must be minimized.
• Interfaces must remain stable during operation.

This makes tandem photovoltaic design a multidisciplinary optimization problem involving materials science, semiconductor physics, optics, chemistry, and device engineering.

Recent reviews emphasize that the rapid efficiency improvements have come from simultaneous advances in perovskite composition, interfacial passivation, charge-selective contacts, recombination layers, and silicon bottom-cell architectures.

The Importance of Wide-Bandgap Perovskites

One of the central materials challenges is developing a wide-bandgap perovskite suitable for the top cell.

For perovskite–silicon tandem devices, the perovskite bandgap is commonly engineered toward approximately 1.65–1.70 eV. This allows the top cell to harvest visible light while transmitting a useful portion of the near-infrared spectrum toward silicon.

Bandgap engineering can involve changing the halide composition, particularly the balance between iodide and bromide.

But increasing the bandgap introduces another major problem:

Halide Segregation

Under illumination or electrical stress, mixed-halide perovskites can undergo compositional redistribution. Regions with different halide compositions can form, creating local bandgap variations.

This can increase voltage losses and compromise the stability of wide-bandgap perovskite devices.

For this reason, wide-bandgap perovskite stability has become one of the central research problems in tandem photovoltaics.

Why Is Interface Engineering So Important?

A tandem device contains many interfaces, and every interface can introduce additional losses.

Defects at surfaces and grain boundaries can create electronic trap states. These traps can promote nonradiative recombination, in which excited carriers lose their energy without contributing to useful electrical current.

The result can be a reduction in:

• Open-circuit voltage.
• Fill factor.
• Carrier lifetime.
• Overall power conversion efficiency.

Researchers therefore use different forms of interface engineering and defect passivation to reduce these losses.

Recent reviews highlight defect passivation, charge-carrier management, and interfacial engineering as major strategies for improving wide-bandgap perovskite devices used in tandem photovoltaics.

This is also where technologies such as self-assembled monolayers, molecular passivation layers, 2D materials, and optimized charge-transport layers become important.

Optical Management: Getting More Photons into the Device

High efficiency is not only a materials problem.

A tandem solar cell must also be designed optically.

The top perovskite cell should absorb the photons that it can convert efficiently while allowing useful wavelengths to reach the silicon cell.

This creates several opportunities for optical engineering:

• Controlling perovskite thickness.
• Optimizing refractive-index matching.
• Reducing parasitic absorption.
• Engineering textured silicon surfaces.
• Improving light coupling between layers.
• Optimizing transparent conductive electrodes.

Transparent conducting electrodes are particularly important because they must simultaneously provide electrical conductivity and optical transparency.

The Efficiency Race: Beyond 35%

The progress of perovskite–silicon tandem photovoltaics has been exceptionally rapid.

The 2026 edition of the Solar Cell Efficiency Tables reported a 35.2% independently confirmed efficiency for a 1 cm² perovskite/Si tandem cell.

In July 2026, LONGi announced a 35.5% certified two-terminal perovskite–silicon tandem cell, with certification by the European Solar Test Installation (ESTI).

These numbers are important, but they need to be interpreted correctly.

A record laboratory cell is not the same thing as a commercial solar module.

The active area, manufacturing process, operating conditions, stability, yield, and production cost all matter.

This distinction is becoming increasingly important as tandem research moves from efficiency records toward commercialization.

Why 35% Efficiency Does Not Mean Commercialization Is Solved

The biggest remaining challenge may no longer be simply achieving another percentage point of laboratory efficiency.

Instead, researchers must answer a much harder question:

Can a tandem solar cell maintain high performance over years of real-world operation and be manufactured economically at large scale?

Recent commercialization research identifies several major barriers, including long-term stability, large-area fabrication, real-world reliability, and degradation caused by both intrinsic and environmental stressors.

Potential degradation mechanisms include:

• Halide segregation.
• Ion migration.
• Interfacial delamination.
• Thermal stress.
• Moisture exposure.
• UV-induced degradation.
• Electrode corrosion.
• Mechanical stress.
• Current mismatch.
• Hotspot formation.

Therefore, tandem solar cell stability is becoming just as important as peak power conversion efficiency.

From Small Cells to Large-Area Modules

Scaling a device from a small laboratory cell to a module introduces another layer of difficulty.

A small-area laboratory device can be carefully fabricated under highly controlled conditions. A module contains a much larger active area and many interconnected regions.

Small variations in:

• Film thickness.
• Crystallization.
• Defects.
• Coating uniformity.
• Interconnection.
• Contact resistance.

can accumulate across the module.

Recent work is therefore increasingly focused on scalable perovskite fabrication, including ambient processing and blade coating.

For example, a 2026 Nature Sustainability study demonstrated ambient-air blade-coated perovskite devices and monolithic perovskite–silicon tandem cells, illustrating the growing emphasis on manufacturing-compatible processes rather than laboratory efficiency alone.

What Are the Most Important Research Directions?

1. Better Wide-Bandgap Perovskites

Researchers need compositions that provide the required bandgap while suppressing halide segregation and voltage losses.

2. Advanced Defect Passivation

Reducing trap-assisted recombination remains essential for increasing voltage and improving operational stability.

3. Interface Engineering

The buried interfaces between the perovskite, transport layers, recombination layers, and silicon subcell require precise control.

4. Improved Transparent Electrodes

Electrodes must provide low electrical resistance without sacrificing optical transmission.

5. Better Silicon Bottom Cells

The performance of the silicon subcell directly affects the overall tandem device.

6. Scalable Manufacturing

Processes such as blade coating, slot-die coating, vacuum deposition, and other large-area techniques must deliver uniform films without sacrificing device performance.

7. Long-Term Reliability

The field increasingly needs standardized testing under realistic thermal, optical, electrical, and environmental conditions.

What Comes After 35%?

The next stage of perovskite–silicon tandem research is unlikely to be defined by efficiency alone.

The central question is becoming:

How can researchers simultaneously optimize efficiency, stability, scalability, and cost?

That shift is already visible in the recent literature. Reviews increasingly treat performance, durability, manufacturability, and commercialization as interconnected engineering problems rather than separate research topics.

This is important because the ultimate value of tandem photovoltaics will depend not simply on whether a laboratory cell reaches another record efficiency, but on whether that performance can be reproduced over large areas and maintained during years of operation.

Conclusion

Perovskite–silicon tandem solar cells have moved from an emerging research concept toward one of the leading areas of next-generation high-efficiency photovoltaics.

The combination of a wide-bandgap perovskite top cell with a silicon bottom cell allows more effective use of the solar spectrum and has pushed certified research-cell efficiencies beyond 35%.

But the next breakthroughs will require more than record numbers.

Wide-bandgap stability, halide segregation, defect passivation, interface engineering, transparent electrodes, scalable fabrication, and long-term reliability are becoming equally important research priorities.

For researchers, this makes perovskite–silicon tandem photovoltaics one of the most interdisciplinary areas in modern solar-cell research—and one where advances in materials chemistry, nanotechnology, optics, and device engineering increasingly converge.