As climate change accelerates and fossil fuels continue to pollute our atmosphere, the world is racing toward cleaner, more sustainable energy solutions. But what often goes unnoticed behind the scenes are the materials— the alloys, nanotechnology, polymers, and crystals that make renewable energy possible. Over the next two weeks, we’ll compare four powerful energy solutions: solar, thermoelectric, geothermal, and hydroelectric; and explore how materials science drives innovation in each. Today, we will discuss solar and thermoelectric energy generation.
Solar/Photovoltaics
Solar panels, or photovoltaic cells, convert light radiation energy into electrical energy. They do this through the photoelectric effect, where, in the orbitals of an atom, photons hitting electrons can make them jump up an energy level while absorbing the photon. But how does this create electricity, or a flow of electrons?
Imagine an array of silicon atoms, they each have four connections to one another in a square lattice. All the covalent bonds between them lock the electrons in place. In this stable state, there is no flow of electrons, but when light hits a valence electron and knocks it up an energy state, it temporarily leaves the covalent bond and other electrons move to fill it, then other electrons move to fill that electron’s bond, creating a cascade of electrical flow. While this isn’t the whole story, as silicon is doped with impurities like boron and phosphorus to increase electrical flow, it paints a picture of the core ideas behind photovoltaics.
Key materials:
- Crystalline silicon (monocrystalline and polycrystalline): still the industry standard. Monocrystalline meaning one crystal, whereas polycrystalline is made of many fragments of silicon crystal.
- Perovskites: an emerging class of materials promising higher efficiency and flexibility.
Perovskites are a more materially optimized crystal structure with promise in photovoltaics.
- Pros: Clean, scalable, and rapidly improving in efficiency.
- Cons: Intermittent (depends on sunlight) and raises sustainability concerns due to rare earth metals required.
Thermoelectric: Turning Heat into Electricity
Thermoelectric generators (TEGs) use temperature differences, such as between a hot road and the cool underground, to create electricity. This works by using a thermocouple, or a pair of two wires made of different materials. These materials have different conductivity, meaning electrons flow at different speeds. Due to entropy, electrons will naturally flow from high heat to low heat, but one wire will have electrons flow faster than the other, creating a net flow of electrons around the wire. This is known as the Seebeck effect.
Key materials:
- Bismuth telluride (Bi₂Te₃): the most common low-temperature TEG material.
- Magnesium silicide, skutterudites, and half-Heusler alloys: for high-temp and industrial use.
- Pros: Works 24/7, can recover waste heat from engines, pavements, or industrial plants.
- Cons: Still low efficiency (~5–8%), and some high-performing materials are expensive or rare.
I hope you learned something new about solar power or thermoelectrics. Next week, we’ll discuss geothermal and hydroelectric energy.