How do photovoltaic cells made with both silicon and perovskite compare?

• A. They are more efficient because they utilize more of the solar spectrum.
• B. They are cheaper but less efficient.
• C. They are identical in efficiency to silicon-only cells.
• D. They are less durable than silicon-only cells.

Answer: (A)

This question hinges on how stacking materials with different light-absorption properties can capture more of the sun’s energy. Silicon and perovskite have different optimal bandgaps, so a tandem cell uses one material to absorb higher-energy photons and the other to absorb lower-energy photons. Perovskite can be tuned to absorb parts of the spectrum where silicon isn’t as strong, while silicon efficiently converts lower-energy photons. When arranged together in a stack and properly current-matched, the overall output increases because more of the solar spectrum is converted into electricity, leading to higher efficiency than silicon alone. There are trade-offs like cost or durability, but the main reason for the efficiency boost is the broader spectrum absorption.