Tandem Cell

What is a tandem cell

A tandem solar cell stacks two or more semiconductor materials with different bandgaps to convert a broader portion of the solar spectrum into electricity. The top cell absorbs higher-energy photons (blue and green light) that would otherwise be partially wasted in single-junction silicon. The bottom cell absorbs lower-energy photons (red and infrared) that pass through the top cell.

The fundamental advantage: each material is optimised for its portion of the spectrum, reducing thermalisation losses. Single-junction silicon is limited by the Shockley-Queisser efficiency ceiling of ~33 percent under standard test conditions. Tandems break this limit by working as multiple cells together.

Terrestrial tandem cells in commercial development pair perovskite (top, wide bandgap) with silicon (bottom, narrow bandgap). Lab cells have exceeded 33.9 percent efficiency under STC (2024). Initial commercial products from Oxford PV achieve 26-28 percent module efficiency. Mass-market adoption is expected 2027-2030.

Why tandem cells matter

Higher efficiency. Breaks single-junction silicon’s ceiling.

Better LCOE potential. More watts per square metre reduces balance-of-system cost.

Future of solar. Likely dominant cell technology by 2035.

Material flexibility. Multiple combinations possible.

Industry transformation. Reshapes module manufacturing.

How tandem cells work

1. Top cell (perovskite or similar): absorbs high-energy photons.
2. Sub-bandgap photons pass through top cell.
3. Bottom cell (silicon): absorbs the remaining lower-energy photons.
4. Current flows through both cells (2T) or independently (4T).
5. Total voltage adds in series for 2T.

Technical deep dive

Tandem types

Material combinations

Efficiency record progression

Theoretical limit

For 2-junction tandem at AM1.5: ~42 percent (Shockley-Queisser).

For 3-junction: ~49 percent.

Practical commercial: 5-10 percentage points below theoretical.

Module efficiency expectations

Real-world applications

Premium terrestrial rooftop (Oxford PV initial market).

EV solar (high efficiency per area).

Space and satellites (III-V tandems).

Concentrator photovoltaics (CPV).

Future utility solar.

Advantages

Higher efficiency than single-junction.

More watts per square metre.

Reduced balance-of-system cost.

Future-ready technology.

Multiple material combinations.

Limitations

Higher cost than single-junction.

Manufacturing complexity.

Limited commercial availability.

Standards still adapting.

Long-term stability of perovskite top cell.

Indian market context

Pre-commercial in India.

R&D growing at IITs and CSIR institutes.

Initial deployment likely through imports.

PLI Tranche III may include tandem manufacturing, building on the ₹45,000 crore already committed to domestic module capacity under the current PLI scheme; see India solar statistics 2026 for the current manufacturing base tandem production would need to scale into.

ALMM listing requires standards updates.

Standards and certifications

Key takeaways

Tandem solar cells stack materials with different bandgaps to break single-junction efficiency limits. Perovskite-silicon tandems exceed 33 percent lab efficiency. Initial commercial production from Oxford PV started 2024. Mass-market adoption expected 2027-2030. India tracking developments with R&D growing. Likely dominant cell technology by 2035.

Tracking tandem cell developments?

Tandem cells are a module technology. Qbits makes on-grid and hybrid inverters, not solar modules, so whichever cell technology a site uses, the solar inverter is matched to the module’s electrical ratings on the module datasheet.

Further reading

For how Tandem Cell plays out in real projects, these guides go deeper:

• Inverter MPPT: 8 Critical Selection Factors (2026)
• MPPT vs PWM Charge Controller Comparison
• Solar Inverter Efficiency: 95% vs 97% vs 98%
• Transformerless vs Transformer Solar Inverters

Sources

• NREL Best Research-Cell Efficiency Chart.
• Oxford PV technical announcements.
• ITRPV Roadmap on tandem cells.
• IEA PVPS Trends 2024.
• Shockley W., Queisser H., Detailed balance limit of efficiency, JAP 1961.
• Yoshikawa K., et al., Silicon heterojunction solar cell with interdigitated back contacts, NREL technical reports.
• IEC TS 63342, Tandem cell test protocols.
• ESIG and IEA PVPS publications on emerging PV.
• Saliba M., et al., Perovskite-silicon tandem cells, Science publications.