Engineered 2D perovskites tandem solar cells reach an almost ideal band gap while improving stability, marking a key step forward for next-generation photovoltaics.
A new approach to improve tandem solar materials
Sometimes, achieving better performance does not require adding complexity, but removing it. This principle may also apply to tandem solar technologies, according to recent research from Rice University on two-dimensional perovskites.
Scientists from the Texas-based university, working with teams in the United States and France, have developed a 2D crystal that is more stable than its three-dimensional counterpart while maintaining strong light absorption. According to the researchers, this result could support meaningful progress in multi-junction solar technologies, an area gaining relevance in fast-growing solar markets, including parts of Sub-Saharan Africa.
The role of perovskites in tandem solar cells
Perovskites have emerged as a key material in tandem photovoltaic technologies due to their ability to tune the band gap. Typically reaching values around 1.7 to 1.8 eV, these materials can efficiently absorb high-energy light while allowing lower-energy photons to pass through. In tandem configurations, this translates into a top cell based on perovskite absorbing visible and ultraviolet light, while a bottom cell, usually made of silicon, captures the near-infrared portion of the spectrum.
On paper, this combination represents an ideal solution. In practice, however, the best band gap performance has traditionally been achieved using three-dimensional perovskites, which remain highly sensitive to moisture and prone to degradation over time.
Why 2D perovskites offer better stability
Two-dimensional perovskites are more resistant to environmental conditions thanks to their structure, which includes hydrophobic organic chains that act as spacers and repel water molecules. However, unlike fully inorganic semiconductors such as silicon, their mixed organic-inorganic composition results in a softer crystal lattice.
This reduced symmetry introduces structural distortions that hinder charge transport and ultimately limit the efficiency of the device. As a result, while 2D perovskites offer improved stability, they have historically struggled to match the performance of their 3D counterparts.
A multilayer structure close to perfect symmetry
The research team led by Aditya Mohite has developed a multilayer 2D perovskite that overcomes these limitations. According to Mohite, the material is “as close to perfect symmetry as one can get in a crystal”, and this behavior has been demonstrated for the first time in a multilayer 2D perovskite system at room temperature.
To achieve this result, the researchers drew inspiration from the structure of the 3D perovskite FAPbI₃, applying advanced crystallization protocols and designing tailored organic molecules. This approach enabled the formation of precise tetragonal structures while reducing the spacing between layers to just 4 Å.
Improved exciton transport and light interaction
The new material shows a significant improvement in exciton transport properties. According to Mohite, all absorbed light generates excitons that can travel through the material for more than two micrometers without losing energy, a result that only a limited number of materials can achieve.
The multilayer configuration also changes how the material interacts with light. While single-layer 2D perovskites typically exhibit a band gap between 2.2 and 2.5 eV, limiting absorption to the violet region, increasing the number of layers reduces the band gap. With three layers, it reaches values around 1.7 to 1.8 eV, enabling absorption across a broader portion of the solar spectrum and making the material suitable for tandem solar applications.
Testing and implications for next-generation photovoltaics
The researchers tested the material in self-powered photodetectors, devices capable of converting light into electrical signals. The results showed higher sensitivity and faster response compared to devices based on other 2D perovskites.
“One of the main challenges for tandem photovoltaic devices is the availability of wide band gap materials,” said Faiz Mandani, co-author of the study. “The 2D perovskites we are developing offer improved 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.
