Contact between 2D and 3D perovskites reshapes crystal order, lifting efficiency to 26.25%

Breaking the Stability Barrier: New 2D/3D Perovskite Interaction Boosts Solar Efficiency to 26.25%

For years, perovskites have been hailed as the “miracle material” of the renewable energy world. These crystal-structured materials can convert sunlight into electricity more affordably and flexibly than the traditional silicon cells that currently dominate the market. However, a persistent Achilles’ heel has held them back: operational stability. Perovskite cells often deteriorate too quickly to be commercially viable.

A recent breakthrough from researchers at Korea University, the University of Toledo, and Seoul National University may have finally solved this puzzle. By leveraging a phenomenon called contact-induced cationic interactions (CCI), the team has developed a method to create near-perfect crystal structures, pushing solar cell efficiency to 26.25% and significantly extending their lifespan.

The Problem with “Imperfect” Crystals

The efficiency of a solar cell depends heavily on the quality of its underlying films. In halide perovskites—specifically $FAPbI_3$, one of the most promising compositions for high efficiency—crystallization is often imperfect. These imperfections, or “trap states,” create defects that lead to energy loss and trigger phase transitions that degrade the material over time.

To fix this, many researchers have historically relied on chemical additives to improve crystallinity. While effective in the short term, the long-term impact of these additives on device stability remains unknown and potentially risky. The goal for the industry has been to achieve a “near-ideal” crystal structure without relying on these unpredictable chemical crutches.

The Breakthrough: Contact-Induced Crystallization

Instead of adding chemicals, Jun Hong Noh and his colleagues focused on the interface between two different types of perovskites: two-dimensional (2D) and three-dimensional (3D) layers. 2D perovskites possess a wide-bandgap, meaning they can absorb high-energy light (like blue or ultraviolet) but not lower-energy light.

The researchers discovered that simply bringing 2D and 3D materials into contact triggered a reversible change in the 3D layer’s optical properties, specifically its photoluminescence. This interaction happens because of the organic cations in the 2D layer interacting with those in the 3D layer.

To lock in these improvements, the team introduced a thermal treatment process. By applying heat and pressure to the contacting layers, they provided the energy necessary for the 3D layer to undergo a structural evolution. The result was an additive-free $FAPbI_3$ film with lattice parameters that nearly match theoretical ideal values.

“Efficiency losses originate from trap states at surfaces and within the bulk, which are directly linked to defects,” explained Jun Hong Noh, senior author of the study. “achieving a near-perfect crystal structure is one of the most critical challenges in this field.”

Real-World Performance: Efficiency and Longevity

The impact of this structural refinement is evident in the hardware’s performance. When integrated into functioning solar cells, the refined films achieved a power conversion efficiency of 26.25%. More importantly, the cells demonstrated remarkable durability, maintaining operational stability for approximately 24,000 hours under accelerated testing.

Beyond the numbers, this method offers two distinct advantages for the industry:

• Additive-Free Fabrication: By removing the need for stabilizers, the team eliminated the risk of unknown long-term degradation caused by foreign chemicals.
• Scalability: The 2D/3D contact process is easier to scale, making it possible to produce larger films with consistently low defect rates.

The Path Forward: Tandem Cells and Low-Temp Processing

The implications of this research extend beyond single-layer cells. The team is now looking toward all-perovskite tandem solar cells. These devices stack a low-bandgap perovskite film on top of a wide-bandgap layer to capture more of the solar spectrum.

Tandem cells are notoriously difficult to manufacture because the top layer must be deposited at low temperatures to avoid damaging the layer beneath it. This usually prevents proper crystallization. The researchers believe their contact-induced strategy can enable high-quality crystal formation even under these temperature constraints, potentially unlocking a new tier of performance for tandem devices.