New Study Reports 28.22% Power Conversion Efficiency Using Lead-Free Perovskite Tandem Architecture

Researchers at the University of Babylon, Iraq, have announced a major advancement in the development of environmentally friendly solar technology. Their latest study presents a lead-free all-perovskite tandem solar cell design that achieved a power conversion efficiency (PCE) of 28.22% through advanced simulation techniques.

The study, titled “High-efficiency lead-free all-perovskite tandem solar cells achieving 28.22% power conversion efficiency: A Cs₂AgBi₀.₇₅Sb₀.₂₅Br₆/FASnI₃ heterostructure design,” was published in the peer-reviewed journal Results in Optics in August 2025.

A Push for Lead-Free Alternatives

Perovskite solar cells are considered one of the most promising next-generation photovoltaic (PV) technologies due to their high efficiencies and low-cost potential. However, most high-performance devices depend on lead-based compounds, which pose environmental and health risks. With growing restrictions on hazardous materials, the search for Pb-free perovskite solutions has gained momentum worldwide.

Innovative Tandem Architecture

In their work, the University of Babylon team proposed a tandem structure combining two distinct lead-free perovskites: Cs₂AgBi₀.₇₅Sb₀.₂₅Br₆ as the wide-bandgap (1.8 eV) top subcell, and FASnI₃ as the narrow-bandgap (1.41 eV) bottom subcell.

By optimizing absorber thicknesses (600 nm for the top and 500 nm for the bottom) and employing SCAPS-1D numerical simulations, the researchers achieved balanced current flow and minimized energy losses. The device reached a fill factor of 88.74%, short-circuit current density of 27.88 mA/cm², and open-circuit voltage of 1.14 V, resulting in the record 28.22% PCE.

Industry Implications

The study underscores that this tandem structure effectively harvests sunlight across the 350–850 nm spectrum, boosting performance in both visible and near-infrared regions. Compared to other lead-free designs, which typically fall below 20% efficiency, the Babylon design demonstrates a clear leap forward. Importantly, the simulated device showed resilience to variations in transport layer thickness, pointing toward practical scalability.

Looking Ahead

Although these results are simulation-based, the authors highlight that the framework provides a strong basis for experimental validation and industrial adaptation. By demonstrating that high-efficiency, lead-free tandem perovskites are achievable, the research paves the way for cleaner, safer, and more scalable solar technologies.