Perovskite solar cells convert sunlight into electricity using a thin layer of crystalline material that absorbs light and generates free-flowing electrons and holes with remarkable efficiency. Unlike silicon solar cells, which need thick, energy-intensive wafers, perovskite cells can be made from liquid solutions painted or printed onto surfaces, potentially at a fraction of the cost. Single-junction perovskite cells have reached 26% efficiency in the lab, and when paired with silicon in a tandem design, that number climbs to nearly 35%.
The Crystal That Makes It All Possible
Perovskite isn’t a single material. It’s a family of crystals that share the same geometric structure, described by the formula ABX₃. In that formula, A and B are two differently sized positively charged atoms, and X is a negatively charged atom (usually a halide like iodine, bromine, or chlorine). The smaller B atom sits at the center of a cage formed by six X atoms, creating an octahedral shape. These octahedra link together in a repeating three-dimensional network, while the larger A atoms nestle into the gaps between them, stabilizing the whole framework.
For solar cells, the most common version uses methylammonium or formamidinium as the A component, lead as the B component, and iodine as the X component. This particular combination produces a material that absorbs visible light extremely well, allows charges to move freely through it, and can be dissolved in solvents for easy processing. The way the octahedra tilt or twist within the lattice changes the crystal’s electronic properties, which gives researchers a powerful lever for fine-tuning performance.
How Light Becomes Electricity
When a photon of sunlight hits the perovskite layer, it transfers its energy to the material and promotes an electron from a lower energy state to a higher one, leaving behind a positively charged “hole.” In many other solar technologies, these electrons and holes initially form a bound pair (called an exciton) that must be actively separated before current can flow. Perovskite skips this step. Because the material has a high dielectric constant and a highly ordered crystalline structure, the binding energy between the electron and hole is so low that light absorption directly generates free, independent charge carriers.
Once free, these electrons and holes need to travel through the material and reach opposite electrodes to create a circuit. Perovskite excels here too. Charge carriers move through perovskite in a smooth, band-like fashion, similar to how electrons move through traditional semiconductors like silicon. Their effective mobility ranges from 0.1 to 10 cm² V⁻¹ s⁻¹, which is tens of thousands of times faster than in organic solar cells. This speed means carriers can reach the electrodes before they recombine and lose their energy, which is one of the main reasons perovskite cells achieve such high efficiencies.
Layers of a Perovskite Solar Cell
A perovskite solar cell is a sandwich of thin layers, each with a specific job. At the core sits the perovskite absorber layer, typically a few hundred nanometers thick. On one side is an electron transport layer (ETL), on the other a hole transport layer (HTL), and the whole stack sits between two electrodes (one of which must be transparent to let light in).
The electron transport layer selectively pulls electrons out of the perovskite while blocking holes. Common ETL materials include titanium dioxide and zinc oxide. The hole transport layer does the reverse, extracting holes while repelling electrons. Nickel oxide is a widely used HTL material. This selective extraction is what creates a net flow of charge in one direction, producing usable electric current. The cell can be built in two orientations: a “standard” configuration where light hits the ETL first, or an “inverted” configuration where light enters through the HTL. Both work, but each has trade-offs in efficiency, stability, and ease of manufacturing.
Tunable Light Absorption
One of the most distinctive features of perovskite is that you can change which wavelengths of light it absorbs by swapping out atoms in the crystal. This is called bandgap tuning, and it’s as straightforward as adjusting a recipe. The bandgap is the minimum energy a photon needs to generate a charge carrier. A narrower bandgap absorbs more of the solar spectrum (including lower-energy red and infrared light), while a wider bandgap captures only higher-energy blue and ultraviolet photons.
Replacing iodine with bromine at the X site widens the bandgap. For methylammonium lead halide, this shift spans from 1.6 eV (good for capturing a broad range of visible light) up to 2.3 eV (selective for blue and UV light). Going the other direction, substituting lead with tin at the B site narrows the bandgap below 1.48 eV, extending absorption into the near-infrared. Formamidinium-based perovskites can be tuned across a similar range, from 1.48 eV to 2.23 eV, by adjusting the halide ratio. Three factors drive these changes: the electronegativity difference between the metal and halide, the angle at which the octahedra connect, and the distance between the metal and halide atoms.
This tunability isn’t just academically interesting. It’s what makes perovskite ideal for tandem solar cells.
Tandem Cells With Silicon
A standard silicon solar cell has a bandgap of about 1.1 eV. It absorbs low-energy photons efficiently but wastes energy from high-energy photons as heat, a process called thermalization. Perovskite solves this problem when layered on top of silicon. The wide-bandgap perovskite top cell absorbs the high-energy blue and green photons, converting them efficiently. The lower-energy red and infrared photons pass through the perovskite and are captured by the silicon cell underneath.
By splitting the solar spectrum between two materials, tandem cells reduce thermalization losses and capture a broader range of sunlight. The results have been dramatic. Monolithic perovskite-silicon tandem cells have climbed from about 13.7% efficiency to approximately 34.85% in under a decade, surpassing the theoretical limits of either material alone. This is widely considered the most commercially promising path for perovskite technology, because it builds on the massive existing silicon manufacturing infrastructure rather than replacing it.
How They’re Made
Perovskite’s manufacturing advantage over silicon is fundamental. Silicon cells require melting raw material at over 1,400°C and slowly growing ingots that are sliced into wafers. Perovskite’s ingredients dissolve in common solvents to form an ink that can be applied at low temperatures.
The simplest lab method is spin-coating: a few drops of precursor solution are placed on a spinning substrate, creating a thin, uniform film that crystallizes after gentle heating. For larger-scale production, researchers have adapted industrial coating techniques. Slot-die coating pushes the ink through a narrow slit onto a moving substrate, producing continuous films compatible with roll-to-roll manufacturing, the same process used to print newspapers. Doctor blading, inkjet printing, and ultrasonic spray coating offer additional scalable options. Fully slot-die-coated cells have already been demonstrated, printing every layer of the device without any spin-coating steps.
Estimated levelized costs of electricity for perovskite cells fall between 3 and 6 cents per kilowatt-hour, competitive with the best mainstream silicon technologies.
The Stability Problem
The biggest barrier to commercial perovskite solar cells is durability. Silicon panels routinely last 25 years outdoors. Perovskite degrades when exposed to moisture, oxygen, heat, and even light itself.
Research published in the Journal of the American Chemical Society detailed the degradation chain reaction in formamidinium-based perovskites. It starts when water molecules dissolve the organic component (formamidinium iodide) at the crystal surface, stripping it away and leaving behind a lead-iodide-rich region. Oxygen then attacks this exposed surface, oxidizing the iodide into iodate compounds that bond to lead atoms and segregate at the surface. This creates vacancies that allow more water to infiltrate deeper into the crystal. As the organic component continues to be lost, the balance of atoms in the crystal shifts into an unstable range, and the perovskite transforms into non-functional phases that no longer absorb light effectively. Water and oxygen work together in a self-reinforcing cycle: water creates the vulnerable surfaces, and oxygen locks in the damage.
Encapsulation (sealing the cell from air and moisture) helps, and researchers are developing more chemically stable perovskite compositions. But proving 25-year outdoor lifetimes remains the field’s central challenge.
The Lead Question
Most high-performing perovskite cells contain lead, which is toxic and raises environmental and regulatory concerns. Tin is the most promising lead-free alternative because it has a nearly identical atomic size (115 pm for tin versus 119 pm for lead) and the same electronic configuration, meaning it slots into the crystal structure with minimal disruption. The first pure tin-based perovskite cell achieved 8.4% efficiency, and mixed formamidinium-methylammonium tin cells have reached 8.12%.
Other candidates include germanium, bismuth, antimony, and copper. Germanium-based cells have so far maxed out around 3.2% efficiency, while bismuth-based devices have reached up to 8% with certain compositions. The gap between lead-free alternatives (topping out around 9%) and lead-based cells (26% and climbing) remains substantial. Tin-based perovskites face their own stability challenge: tin readily oxidizes from its +2 state to +4, which destroys the perovskite structure even faster than moisture degrades lead-based versions.