Technology
Perovskite–Silicon Tandem Solar Cells for High-Efficiency Photovoltaics
Quick fact
Perovskite–silicon tandem cells have achieved efficiencies above 30% in the lab, surpassing the theoretical maximum for single-junction silicon cells (about 29%).
Why this is interesting
You've seen silicon solar panels on rooftops, but what if we could squeeze more power from the same sunlight? Scientists have found a way to stack two different materials to capture more of the sun's energy—boosting efficiency beyond what silicon alone can achieve.
Read the full explanation
Understanding Perovskite–Silicon Tandem Solar Cells for High-Efficiency Photovoltaics
Think of a solar cell as a 'light-eating' device. Silicon can only absorb photons with enough energy to excite electrons across its bandgap—photons with less energy are wasted, and photons with much more energy waste the excess as heat. A perovskite–silicon tandem cell places a perovskite layer (with a higher bandgap) on top of a silicon layer (with a lower bandgap). The perovskite absorbs high-energy photons (blue/green light), while silicon absorbs lower-energy photons (red/infrared). This way, the cell uses the sunlight more efficiently, generating higher voltage and more power from the same area.
A deeper explanation
The key to this efficiency boost is the Shockley-Queisser limit, which sets the maximum efficiency for a single-junction cell (~33%). By stacking two cells with different bandgaps, each junction can be optimized for a portion of the solar spectrum, reducing thermalization and transmission losses. In a tandem, the top perovskite cell (bandgap ~1.7 eV) absorbs high-energy photons, and the bottom silicon cell (bandgap ~1.1 eV) captures the rest. For maximum efficiency, the two subcells must be 'current-matched'—they generate the same current so that no current is lost. This is achieved by adjusting the perovskite bandgap and the thickness of the layers. The perovskite layer also helps by generating a high voltage, while silicon provides stability and a low-cost base. The result is a cell that can surpass 30% efficiency, a milestone that silicon alone cannot reach. This technology is crucial for making solar power more powerful and cost-effective, potentially enabling more energy generation per acre and reducing the cost per watt.