Technology
Perovskite-Silicon Tandem Solar Cells Exceeding 30% Efficiency
Quick fact
In 2024, a perovskite-silicon tandem cell reached an efficiency of 33.9%, shattering the long-standing 33.7% limit for single-junction silicon.
Why this is interesting
Solar panels you see on rooftops are typically around 20% efficient—but what if a single panel could convert over 30% of sunlight into electricity? That's exactly what has been achieved by stacking a mysterious material called perovskite on top of silicon.
Read the full explanation
Understanding Perovskite-Silicon Tandem Solar Cells Exceeding 30% Efficiency
Imagine a solar cell as a net that catches particles of light (photons) to generate electricity. But the net has a limited mesh size: it only catches certain photon energies. Silicon, the standard material, is best at catching photons from the red and near-infrared part of sunlight, but it lets many high-energy (blue) photons slip through, wasting their energy. Perovskite, on the other hand, is excellent at catching blue and green photons. In a tandem cell, we place a thin perovskite layer on top of a silicon cell. The top layer absorbs the high-energy photons while letting the low-energy ones pass through to the silicon below. This stacks two 'nets' with different mesh sizes, catching more of the sunlight's energy than either could alone.
A deeper explanation
The key to this breakthrough lies in the concept of bandgap—a material's property that determines what photon energies it can absorb. Silicon has a bandgap of about 1.1 eV, which is optimal for the red part of the spectrum. Perovskite can have its bandgap tuned (by changing its chemical composition) to around 1.7 eV, ideal for blue light. In a tandem configuration, the perovskite top cell absorbs high-energy photons, generating a high voltage while letting lower-energy photons pass through. The silicon bottom cell then absorbs these and produces additional voltage. The combined voltage is the sum of the two cells, and the current is limited by the lower of the two. By carefully engineering the two layers, researchers have achieved efficiencies above 30%, surpassing the maximum possible efficiency of a single-junction silicon cell (about 29.4%). This not only increases power output per unit area but also reduces the per-watt cost of solar energy, making it a key technology for the future.