What Is a Solar Cell?

At its core, a solar cell is a semiconductor device that converts sunlight directly into electricity through the photovoltaic effect. When a photon of sufficient energy strikes the semiconductor, it knocks an electron loose, and the cell's internal electric field sweeps that electron toward a contact, generating current.

The catch is that no single material can absorb the full spectrum of sunlight efficiently. Every semiconductor has abandgap - an energy threshold below which photons pass straight through, and above which any excess photon energy is lost as heat. That single-material ceiling is the fundamental reason single-junction silicon cells plateau around 29% efficiency in theory, and closer to 22–24% in commercial production.

Silicon Photovoltaics: The Workhorse of the Industry

Crystalline silicon (c-Si) has dominated solar manufacturing for decades, and for good reason. It's abundant, non-toxic, extremely stable - panels routinely carry 25-year performance warranties - and the industry has spent thirty years driving down the cost of producing high-purity silicon wafers at scale.

But silicon's bandgap (about 1.1 eV) is tuned to absorb red and infrared light efficiently while wasting much of the energy in blue and green photons as heat. Decades of process refinement (PERC, TOPCon, HJT) have pushed commercial cells close to their theoretical single-junction limit. Getting meaningfully past that ceiling requires a fundamentally different architecture - not a better silicon cell, but a second cell stacked on top of it.

What Is Perovskite?

"Perovskite" refers to any material sharing the crystal structure of the mineral calcium titanium oxide. In photovoltaics, the term usually means a class of synthetic metal-halide perovskites (commonly lead- or tin-halide compounds) that can besolution-processed - deposited from a liquid ink rather than grown as an ingot and sliced, the way silicon wafers are made.

Perovskites have two properties that make them an ideal partner for silicon. First, their bandgap is tunable - adjusting the chemical composition shifts which part of the spectrum the material absorbs best. Second, they absorb light very strongly, so a layer just a few hundred nanometers thick can capture a large share of incoming high-energy photons that silicon would otherwise waste as heat.

How Tandem Cells Work: Stacking for Efficiency

A tandem cell stacks two sub-cells with different bandgaps on top of one another so each absorbs the part of the solar spectrum it handles best:

• Top cell (perovskite): tuned to a wide bandgap, it absorbs high-energy blue and green photons and lets lower-energy light pass through to the layer below.
• Bottom cell (silicon): absorbs the red and infrared light the perovskite layer transmits, using the same narrow-bandgap advantage that made silicon efficient in the first place.

Because each sub-cell operates closer to its own optimal bandgap instead of one material compromising across the whole spectrum, the combined stack loses far less energy to heat. That's the entire reason tandem architectures can push past the single-junction limit - lab cells from groups like Oxford PV and KAUST have already demonstrated 33%+ conversion efficiency, well above what silicon alone can achieve.

Critically, most commercial tandem roadmaps build the perovskite layer directly on top of a conventional silicon cell using existing fab lines - meaning tandem isn't a replacement technology so much as an upgrade layer for the manufacturing base the industry has already built.

Why It Matters for Buyers

For installers, EPCs, and asset owners, panel efficiency is a direct lever on the economics of every project:

A jump from silicon's 22% to tandem's 25% commercial efficiency today, heading toward 27%+ by 2027, isn't an incremental spec bump - it's a meaningful increase in energy yield from the same footprint, which materially changes the levelized cost of electricity (LCOE) math for a project.

From Lab to Fab: The Commercialization Timeline

Tandem technology has moved from academic curiosity to pre-commercial production faster than most PV innovations:

• 2012–2018: Rapid lab-scale efficiency gains establish perovskite-silicon tandem as a credible research path.
• 2019–2022: Record cell efficiencies repeatedly broken; pilot lines announced by early movers.
• 2023–2025: First commercial-scale tandem modules reach limited production and early customer shipments.
• 2026 and beyond: Scaling of gigawatt-class manufacturing capacity as stability data accumulates and bankability improves.

Key Challenges: Stability & Degradation

Tandem technology isn't without open questions, and any B2B buyer evaluating suppliers should understand them:

• Long-term stability: perovskite materials have historically degraded faster than silicon under heat, humidity, and UV exposure. Encapsulation and compositional engineering have closed much of this gap, but multi-decade field data is still being collected.
• Lead content: most high-performing perovskites use small amounts of lead. Manufacturers are investing in encapsulation standards and lead-free alternatives to address environmental and regulatory scrutiny.
• Manufacturing yield: depositing a uniform, defect-free perovskite layer at gigawatt scale is a harder manufacturing problem than mature silicon processing, and yield is a key driver of near-term cost.

Glossary of Key Terms

Bandgap

The minimum photon energy a semiconductor can absorb to generate an electron-hole pair.

Tandem cell

A solar cell combining two or more sub-cells with different bandgaps to capture more of the solar spectrum.

Perovskite

A class of solution-processable, tunable-bandgap crystal materials used as the top cell in most commercial tandem designs.

PCE (Power Conversion Efficiency)

The percentage of incoming solar energy a cell converts into usable electrical power.

LCOE

Levelized Cost of Electricity - the average lifetime cost of generating power from an energy asset.