A new step forward for tandem photovoltaics efficiency
Sometimes, achieving better performance is not about adding complexity, but removing it. That principle may now apply to tandem solar cells, according to new research from Rice University on two-dimensional perovskites.
Researchers collaborated with teams in the United States and France to develop a 2D crystal that is more stable than its 3D counterpart while maintaining strong light absorption capabilities. According to the team, this breakthrough could unlock meaningful advances in multi-junction solar technologies.
The role of perovskite in tandem solar
Perovskite has emerged as a key material in double- and triple-junction photovoltaics. The reason lies in its tunable properties: these synthetic materials can be engineered with a wide band gap of 1.7–1.8 eV, allowing them to absorb high-energy light while letting lower-energy wavelengths pass through.
In a tandem architecture, this translates into a perovskite top cell capturing photons in the orange, yellow, green, blue, and UV range, stacked above a silicon bottom cell, which absorbs near-infrared light thanks to its narrower band gap.
While this configuration appears ideal in theory, real-world performance has been limited. The best band gap performance has traditionally been achieved with 3D perovskites, which are highly sensitive to moisture and prone to degradation over time.
The structural limits of 2D perovskites
Two-dimensional perovskites offer greater resistance thanks to their structure, which incorporates long hydrophobic organic chains that repel water molecules.
However, unlike fully inorganic semiconductors such as silicon, which form highly ordered and symmetrical crystal structures, 2D perovskites combine organic and inorganic components, resulting in a softer lattice that is more prone to distortion.
In practical terms, this lack of symmetry hinders charge transport and ultimately limits device efficiency.
A multilayer 2D perovskite with near-perfect symmetry
The research team, led by Aditya Mohite at Rice University, developed a multilayer 2D perovskite that overcomes these distortions and approaches near-perfect crystal symmetry.
“As far as we know, this is the first time such a result has been demonstrated in a multilayer 2D perovskite system at room temperature,” Mohite said.
To achieve this, researchers drew inspiration from the 3D perovskite FAPbI3, engineering an improved 2D version using tailored crystallization protocols and custom-designed organic molecules. This enabled the formation of precise tetragonal structures, reducing interlayer spacing to just 4 Å.
The result was a dramatic improvement in exciton transport properties, both in diffusion length and mobility.
“All absorbed light generates excitons that can travel more than two micrometers through the material without energy loss,” Mohite explained. “This is a remarkable outcome, as very few materials can achieve this.”
Band gap tuning through multilayer design
The approach also enabled the creation of thicker, multilayer structures, fundamentally altering how the material interacts with light.
Single-layer 2D perovskites typically exhibit a band gap of 2.2–2.5 eV, limiting absorption to the violet region. By stacking additional layers, researchers reduced the band gap to 1.7–1.8 eV at three layers, enabling absorption across a broader portion of the solar spectrum.
Testing the new 2D perovskites
The material was tested in self-powered photodetectors, devices that convert light into electrical signals. Compared to conventional 2D perovskite-based devices, the new prototypes showed significantly higher sensitivity and responsiveness.
“One of the main challenges in tandem photovoltaics is the availability of wide band gap materials,” said Faiz Mandani, former PhD student at Rice University and co-author of the study. “The 2D perovskites we are developing offer greater stability, and this specific material has a nearly ideal band gap for integration with silicon or other semiconductors.”
The study, titled Exciton diffusion beyond 2 μm enabled by maximum symmetry in two-dimensional perovskites, was published in Nature Synthesis.