Key Findings
A collaborative research team has developed a method to enhance perovskite film quality, resulting in solar cells with a certified power conversion efficiency (PCE) of 25.9% (reaching 26.5% in some instances). The approach also proved effective for larger-scale devices, with perovskite minimodules exceeding 15 square centimeters achieving 23.9% efficiency. Additionally, the technique was applied to perovskite light-emitting diodes, which reached an external quantum efficiency of 26.1%.
Technical Details
The team improved film growth by adding a eutectic mixture of zinc bromide and methylammonium chloride to the perovskite ink. This mixture melts at a lower temperature than its individual components. During the annealing process, the eutectic locally melts around grain boundaries, allowing crystals to rearrange into a more orderly structure. Nanoprobe X-ray microscopy was used to observe this process.
The chemical dynamics during annealing are as follows:
- Methylammonium chloride evaporates from the film.
- Zinc remains at the interfaces and grain boundaries to passivate defects.
- The distribution of halides across the film is leveled.
The resulting films exhibited low surface recombination velocity, long charge carrier decay times, and high photoluminescence quantum yield.
Stability and Versatility
Stability tests on small-area cells utilizing a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) hole transport layer showed that the devices retained 85.8% of their initial 24.1% efficiency after 1,400 hours of continuous operation at 85°C. The researchers confirmed that this eutectic approach is compatible across various perovskite compositions.
Significance and Outlook
By removing performance-limiting defects at the edges of crystalline grains, this method addresses a primary bottleneck in perovskite performance, particularly for larger devices. The research involved a wide consortium including the University of California San Diego, Sungkyunkwan University, Princeton University, and nine other institutions. The team is currently investigating other eutectic chemistries to further optimize performance.
Source: https://www.perovskite-info.com/perovskite-solar-cells-reach-259-efficiency-short-lived-liquid-stage
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