Technology
Perovskite Tandem Solar Cells: A Path to Higher Efficiency Limits
Quick fact
Perovskite-silicon tandems have already reached over 30% efficiency in the lab, surpassing the ~29% practical limit of silicon-only cells.
Why this is interesting
Solar panels today capture only a fraction of the sun's energy. What if we could stack two cells, each tuned to a different color, to nearly double that limit?
Read the full explanation
Understanding Perovskite Tandem Solar Cells: A Path to Higher Efficiency Limits
Think of solar cells as ears for light: each material 'hears' (absorbs) only certain pitches (wavelengths) of sunlight. Silicon, the classic solar material, is great at absorbing red and infrared light but wastes high-energy blue and green photons as heat. Perovskite, a newer material, can be tuned to absorb those high-energy colors efficiently. A tandem cell is like having one ear for treble and one for bass: you put a perovskite cell on top to catch the blue/green light, and let the red/infrared light pass through to a silicon cell underneath. This way, each cell converts the part of the spectrum it handles best, boosting overall efficiency beyond what either could achieve alone.
A deeper explanation
Why does stacking work? A single-junction solar cell has a fundamental efficiency limit (Shockley-Queisser) because it can only convert photons with energy above its bandgap into electricity. Photons with too little energy pass through unused, and photons with too much energy waste extra energy as heat. A tandem cell uses two different bandgaps: the top cell has a larger bandgap, capturing high-energy photons; the bottom cell has a smaller bandgap, capturing the rest. By splitting the spectrum, the tandem reduces energy losses and pushes efficiency higher. Perovskite is ideal because its bandgap can be tuned by tweaking its chemical composition, allowing it to match silicon (1.1 eV) with a ~1.7 eV top cell. This synergy is why perovskite-silicon tandems are a leading contender to exceed the efficiency limits of single-junction solar cells, with the potential to lower the cost of solar electricity.