Abstract

Scaling perovskite solar cells (PSCs) into large-area modules requires precise control of structural uniformity and mechanical integrity. However, scalable deposition often introduces mesoscale heterogeneities, including grain-orientation disorder and lattice-strain gradients, which limit efficiency and stability. Here, we report an intact-film orthogonal two-dimensional X-ray diffraction mapping (2DXDM) technique that enables full-field, quantitative crystallographic analysis of large-area perovskite films without physical sectioning. The method resolves spatial variations in crystallinity, orientation coherence, and lattice strain across complete modules and is validated against conventional sectioned analyzes such as grazing-incidence wide-angle X-ray diffraction (GI-WAXD) and X-ray diffraction (XRD). Using this approach, we compare static spin-coating (SSC) and dynamic spin-casting (DSC). DSC yields more homogeneous films with relaxed lattice stress and controlled solvate evolution, thereby reducing edge defects. As a result, DSC-based modules achieve 23.0% efficiency (22.7% certified) over 86.4 cm2 and retain over 80% of their initial efficiency after 1,000 h of operation.

Perovskite solar cells (PSCs) have reached impressive efficiencies at laboratory scale, but maintaining that performance in larger modules remains challenging. As the films grow larger, differences in crystal orientation and internal strain can develop across the surface, creating defects that reduce efficiency and long-term stability. 

A research team led by Professors Dong-Seok Kim and Jin Young Kim of the School of Energy and Chemical Engineering and Professor Tae Joo Shin of the Graduate School of Semiconductor Materials and Devices Engineering at UNIST, together with Dr. Yun Seop Shin of the Korea Research Institute of Chemical Technology (KRICT), has developed an X-ray technique that maps these structural variations across an intact perovskite film.

Called two-dimensional X-ray diffraction mapping (2DXDM), the technique shows how crystallinity, crystal orientation, and residual strain vary across an entity film without damaging it. Conventional methods often examine selected regions, provide averaged measurements, or require samples to be cut into sections.

PSCs are made by depositing a liquid precursor onto a surface, where it dries and crystallizes into a light-absorbing layer. Across a large area, differences in drying and crystallization can leave the center and edges with different structural properties.

The researchers used 2DXDM to compare two methods for forming large-area films. In static spin-coating (SSC), the precursor solution is applied before the substrate is spun, while dynamic spin-casting (DSC) deposits the solution drop by drop as the substrate rotates.

The resulting maps showed that DSC produced more homogeneous films, with more consistent crystal orientation and lower residual strain. Additional X-ray measurements linked this improvement to better control over colon drying and crystal formation, which helped reduce structural defects near the edges. 

The more uniform films also delivered strong performance at module scale. DSC-based modules reached a power conversion efficiency of 23.0% over an active area of 86.4 cm², with a certified efficiency of 22.7%. Encapsulated modules retained more than 80% of their initial efficiency after 1,000 hours under continuous illumination.

“Conventional methods make it difficult to see how structure varies across an entire film, and cutting a sample for analysis can alter the strain already present” said Professor Shin. “With 2DXDM, we can examine the full area without damaging the film and identify where structural differences occur.”

Professor Dong-Seok Kim added, “For large-area perovskite films, what matters is structural uniformity across the entire surface, not just at a few individual points. By showing how fabrication conditions affect that uniformity, this approach can help guide the development of more efficient large-area modules.”

Dong Shin Kim of the Graduate School of Semiconductor Materials and Devices Engineering and Jae Hwi Lee of the School of Energy and Chemical Engineering at UNIST, served as first authors. The research used the UNIST-PAL 6D beamline at the Pohang Accelerator Laboratory.

The findings were published online in     Joule  on July 23, 2026. The research was supported by the Ministry of Science and ICT (MSIT), Ministry of Education (ME), National Research Foundation of Korea (NRF), Ministry of Trade, Industry and Energy (MOTIE), Korea Institute of Energy Technology Evaluation and Planning (KETEP), Korea Institute for Advancement of Technology (KIAT), and Korea Research Institute of Chemical Technology (KRICT).

Journal Reference

Dongshin Kim, Jaehwi Lee, Dongmin Lee,       et al ., “Intact-film orthogonal 2D X-ray diffraction mapping for crystallographic homogeneity evaluation in perovskite solar modules,”       Joule , (2026).