New Molecule Nearly Doubles Efficiency and Stability of Lead-Free Solar Cells

Most high-performing perovskite solar cells, a promising alternative to conventional silicon panels, rely on lead, which is poisonous and, researchers say, limited in its commercial viability. Tin is a potential lead-free replacement, but tin-based perovskite cells have historically been far less efficient and stable than their lead counterparts. Researchers at Sophia University in Japan, led by Professor Yuko Takeoka, report that adding a small molecule called 2-aminobenzothiazole (2-ABZ) to tin-halide perovskite cells substantially improves both.

In the study, cells treated with 2-ABZ reached a power conversion efficiency of 9.07%, compared with 6.6% for untreated control devices. The treated cells also proved far more durable: they retained 84.94% of their initial efficiency after 100 days of storage, compared with 48.95% for untreated cells, and kept 89% of their functionality after 10 hours of simulated sunlight exposure, while untreated cells degraded rapidly within the first hour.

According to the research, 2-ABZ acts as a "multifunctional molecular stabiliser" throughout the cell, regulating how the perovskite material crystallizes, reducing defect-trapping sites, preventing ions from migrating, inhibiting the tin from oxidizing, and improving how energy aligns across internal interfaces. Takeoka said the buildup of 2-ABZ at the interface is crucial for decreasing buried defects in the perovskite layer by creating densely populated nucleation sites at its base, producing a higher-quality, more stable film. "The findings from our research showed the way for developing safer lead-free solar cells, which could help expand the use of photovoltaic cells," Takeoka said.

The Sophia University team is pursuing lightweight, flexible and shape-controllable perovskite cells for potential niche applications, while other companies pursue industrial-scale commercial production: Caelux is producing perovskite-laced solar glass in the US, and Oxford PV, a technology and patent leader in the field, has licensed its perovskite technology to several large-scale solar manufacturers.