Perovskite solar cells achieve 24% efficiency with novel iodine technique

A team led by Professor Zhou Huanping from Peking University has published two papers in the field of perovskite solar cells in Science.

“Wafer-scale monolayer MoS₂ film integration for stable, efficient perovskite solar cells” was published on January 9, 2025, and “Nonalloyed α-phase formamidinium lead triiodide solar cells through iodine intercalation” was published on January 16, 2025.

Given its photovoltaic properties, low cost and thermal stability, formamidinium lead triiodide (FAPbI₃) has served as a competitive optimal absorber for high-efficiency single-junction perovskite solar cells but is prone to complex crystallization kinetics and thermodynamic metastability at room temperature, presenting huge challenges in its crystallization quality and stability in practical applications.

While alloying strategies such as adding methylammonium hydrochloride and Cs⁺ can effectively control the crystallization process and photoelectric properties of formamidinium-based perovskites films, it may leave behind residual compositional additives that often lead to cation-anion separation, thermal decomposition and potential nucleophilic reactions.

Such obstacles complicate the preparation of high quality, non-alloyed α-FAPbI₃ perovskite films and related devices.

Professor Zhou, alongside her project group, proposed an innovative iodine intercalation-decalation strategy to produce high-quality, nonalloyed α-FAPbI₃ perovskite films, thereby improving the efficiency and stability of perovskite solar cells.

The strong bonding between cogenetic iodine (I₂) and I⁻ forms polyiodide ions, which changes the original FAI+PbI₂→FAPbI₃ reaction path to FAI₃+PbI₂→FAPbI₃+I₂, which is conducive to overcoming the barrier in α-FAPbI₃ formation.

Furthermore, owing to its volatility property, I₂ is removed from the lattice during annealing, ensuring the absence of any extrinsic residue on the high-quality, nonalloyed α-FAPbI₃ film.

The nonalloyed α-FAPbI₃ film produced from the iodine intercalation-decalation reaction demonstrates a substantial improvement in the crystal quality and uniformity. In addition, enhanced thermal stability of the film inhibits ion migration.

The nonalloyed α-FAPbI₃ film-based solar cells exhibited a power conversion efficiency of over 24% and retained 99% of their original efficiency after more than 1,100 hours of operation at 85°C under illumination.

This work underscores Professor Zhou and her team’s innovations in photovoltaic technology, addressing the challenges in achieving stability and high efficiency in perovskite solar cells.