The work focuses on controlling the nanoscale arrangement of donor and acceptor materials within the active film. The research team stated that "The VTA process accelerates solvent evaporation while promoting favorable molecular organization". Under VTA, donor components accumulate toward the bottom of the film and acceptor components toward the top, creating a stratified but connected pseudo-bulk heterojunction with a p-i-n-type profile that supports charge transport and extraction.
Using characterization tools including X-ray photoelectron spectroscopy depth profiling and grazing-incidence wide-angle X-ray scattering, the team found that VTA-treated films show higher molecular order and tighter p-p stacking than films produced by standard processing routes. This improved packing led directly to higher device performance, with champion cells reaching a power conversion efficiency of 20.5 percent.
Stability tests under continuous illumination showed that conventional devices retained 80 percent of their initial output (T80) for more than 3,900 hours. In device architectures optimized for stability, the extrapolated T80 lifetime increased to about 54,000 hours, which is among the longest lifetimes reported so far for organic solar cells combining high efficiency with extended operational stability.
The researchers noted that "The enhanced crystallinity and suppressed phase separation created by VTA treatment establish a robust morphological structure that resists degradation". Additional measurements indicated that VTA-treated films undergo less structural relaxation and domain coarsening when exposed to thermal stress, which explains the improved resistance to performance loss.
The VTA approach was validated across several material systems, including PM6/L8-BO, D18/L8-BO, and the all-polymer combination PM6/PY-IT, indicating that the process can be applied broadly in organic solar cell fabrication. The study shows that relatively simple post-processing can address the trade-off between high efficiency and long-term stability, supporting future development of flexible, lightweight organic photovoltaic modules for practical use.
Research Report:Vacuum-assisted vertical component distribution in pseudo-bulk heterojunctions: a pathway to high-performance and stable organic solar cells
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Wuhan University of Technology
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