Why 2D perovskites could unlock next-generation tandem solar cells
Sometimes, achieving better performance means simplifying rather than adding complexity. This principle appears to hold true for tandem photovoltaics, according to new research led by Rice University.
An international team of scientists has developed a two-dimensional perovskite crystal that combines enhanced stability with strong light absorption, addressing one of the key trade-offs in multijunction solar technologies.
The role of perovskites in tandem photovoltaics
Perovskite materials have emerged as a central component in tandem solar cells, particularly in double and triple junction architectures. Their key advantage lies in their tunable electronic properties.
By engineering a wide band gap (1.7–1.8 eV), perovskites can efficiently absorb high-energy photons while allowing lower-energy light to pass through. In a tandem configuration, this enables a top perovskite layer to capture visible and ultraviolet light, while a bottom silicon cell absorbs near-infrared wavelengths.
In theory, this combination delivers optimal efficiency. In practice, however, the best band gap performance has traditionally been achieved with three-dimensional perovskites, which are highly sensitive to moisture and prone to degradation.
Stability versus performance in 2D perovskites
Two-dimensional perovskites offer a more stable alternative. Their structure incorporates hydrophobic organic chains that act as spacers, protecting the material from humidity.
However, this comes at a cost. Unlike fully inorganic semiconductors such as silicon, which form highly ordered crystal lattices, 2D perovskites tend to have a softer, less symmetrical structure. This structural distortion limits charge transport and reduces device efficiency.
A breakthrough in multi-layer 2D perovskites
The research team, led by Aditya Mohite, designed a multilayer 2D perovskite that overcomes these limitations. The material achieves a structure described as “as close to perfect symmetry as possible in a crystal” at room temperature.
To reach this result, the scientists drew inspiration from the 3D perovskite FAPbI3, creating an improved 2D version through precise crystallisation protocols and custom-designed organic molecules.
This approach enabled the formation of tetragonal space groups and reduced the interlayer distance to just 4 Å, significantly improving exciton transport properties.
“All the absorbed light forms excitons that can travel more than two micrometres without losing energy,” Mohite explained. “Very few materials can achieve this.”
Band gap tuning and improved light absorption
The innovation also changes how 2D perovskites interact with light. Single-layer structures typically have a band gap of 2.2–2.5 eV, limiting absorption to high-energy violet light.
By stacking multiple layers, the researchers were able to reduce the band gap to the ideal range of 1.7–1.8 eV, enabling absorption across a broader portion of the solar spectrum.
This makes the material particularly suitable for integration into tandem photovoltaic devices, where band gap alignment is critical for maximising efficiency.
Testing and future applications of 2D perovskites
The new material was tested in self-powered photodetectors, devices that convert light into electrical signals. Compared to existing 2D perovskites, the prototypes demonstrated higher sensitivity and faster response times.
“Wide band gap materials remain one of the main challenges in tandem photovoltaics,” said Faiz Mandani, co-author of the study. “The 2D perovskites we are developing offer greater stability, and this specific material has a band gap that is nearly ideal for pairing 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.