Perovskite solar cells (PSCs) are a promising next-generation photovoltaic technology that can achieve high power conversion efficiencies. However, their performance and long-term stability are limited by problems that arise both during their manufacture and operation. As perovskite films form, poorly controlled crystallization can produce structural defects and internal strain. Once the cells are operating, ions can migrate through the material under light, heat, and electric fields, further contributing to degradation and making it difficult to maintain high performance in large-area devices.
Now, Chinese researchers have developed a Prussian blue (PB)-based strategy to regulate both crystallization and ion migration processes in PSCs, achieving high power conversion efficiencies from small-area cells to 30 cm × 30 cm submodules.
This strategy achieved a power conversion efficiency (PCE) of 26.9% in small-area cells and was further validated at larger scales, reaching 23.4% in 6 cm × 6 cm minimodules and a certified efficiency of 22.9% in 30 cm × 30 cm perovskite submodules.
The study was published in Science on September 24.
PSCs have attracted considerable attention for their outstanding photovoltaic performance and potential for large-scale applications. However, their thin-film formation is often complicated by uncontrolled nucleation, intermediate-phase evolution, residual strain, lattice disorder, and ionic defects.
These structural imperfections can accelerate ion migration under operating conditions, including light illumination, thermal stress, and electric fields, limiting device efficiency, stability, and scalability.
To address these challenges, the researchers introduced a lattice-compatible PB framework as a structural template and employed advanced synchrotron-based characterization techniques at the Beijing Synchrotron Radiation Facility (BSRF) of the Institute of High Energy Physics of the Chinese Academy of Sciences to investigate the underlying mechanisms.
Using the 1W1A and 1W1B beamlines, the researchers performed in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray absorption fine structure (XAFS) measurements, respectively, to examine the role of PB in crystallization kinetics and local coordination chemistry.
In situ GIWAXS measurements revealed that the PB framework regulated the crystallization pathway of perovskite films by transforming uncontrolled homogeneous nucleation into a more ordered heterogeneous nucleation process. PB suppressed the formation of solvated intermediates and non-photoactive δ-FAPbI3 phases while facilitating a more direct transition toward the photoactive α-FAPbI3 phase. This controlled crystallization promoted preferential crystal growth along the (100) orientation and significantly alleviated tensile lattice strain within the perovskite films.
Further XAFS analysis showed that the PB framework maintained its structural integrity during cation incorporation and redox processes. Even after Cs+ ions were introduced into the PB lattice channels, Fe3+ species underwent reduction while the characteristic Fe–C≡N–Fe cubic coordination framework remained intact, with negligible variation in the primary coordination distances.
These results indicate that PB can simultaneously accommodate and immobilize mobile cations while preserving its robust framework structure, providing a structural basis for continuously regulating defect evolution and suppressing ion migration during device operation.
Synchrotron characterization played an important role in uncovering these underlying mechanisms. At the BSRF 1W1A diffuse scattering beamline, senior engineer CHEN Yu developed and optimized a compact in situ measurement platform that enabled dynamic GIWAXS monitoring of perovskite film formation, including precursor solution coating, antisolvent treatment, and thermal annealing under an inert atmosphere.
At the BSRF 1W1B XAFS beamline, Associate Researcher AN Pengfei worked with the research team to optimize the XAFS measurements and obtain high-quality Fe K-edge spectra. Combined with X-ray absorption near-edge structure (XANES) analysis, extended X-ray absorption fine structure (EXAFS) fitting, and wavelet transform analysis, these measurements systematically characterized the local coordination environment and structural evolution of PB.
According to the researchers, these synchrotron-based investigations provide important experimental support for understanding how PB regulates perovskite crystallization, defect evolution, and ion migration, offering new insights into the development of efficient and stable large-area perovskite photovoltaic technologies.
