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Polycrystalline formamidinium lead iodide (FAPbI3) has emerged as a leading material in the production of perovskite-based solar cells due to its excellent optoelectronic characteristics. However, its crystalline structure is often marred by defects. In an innovative approach, researchers at the Gwangju Institute of Science and Technology (GIST) have introduced a hexagonal polytype perovskite (6H) into the existing cubic polytype (3C) FAPbI3. This strategy has resulted in enhanced power conversion efficiency and greater operational stability for perovskite solar cells compared to traditional configurations.
The transition to solar energy is critical in reducing reliance on fossil fuels and fostering a cleaner energy landscape. Over the years, remarkable advancements have been made in solar cell technology, particularly in materials that can effectively harness this renewable energy source.
Among the notable materials, metal-halide perovskite has garnered significant attention as a highly effective light-absorbing medium for solar cells. Its remarkable optoelectronic properties allow for efficient energy conversion from sunlight, making it a popular choice in the field.
FAPbI3 stands out for its narrow energy band gap, making it a favored option for high power conversion efficiency (PCE) perovskite solar cells. Despite these advantages, polycrystalline perovskites like FAPbI3 frequently encounter defects in their crystalline structures. These imperfections can adversely impact structural stability and carrier dynamics, ultimately limiting the efficacy of energy conversion.
To tackle this issue, a team led by Professor Hobeom Kim from GIST has pioneered a novel defect passivation method aimed at reducing defects and enhancing the PCE and stability of perovskite solar cells. Their findings, published on July 4, 2024, in Nature Communications, highlight the introduction of 6H perovskite into the cubic polytype FAPbI3 as a significant advancement for improving performance metrics in these solar cells.
But what makes the 6H perovskite polytype advantageous? Prof. Kim notes, “Traditionally, external chemical reagents have been used to address defect issues. However, these can compromise the crystalline quality during growth. Our approach circumvents the use of stabilizers by integrating a chemically identical polytype. The 6H version includes components that effectively mitigate defect formation within the perovskite.”
In their experiment, the research team introduced additional lead iodide and methylammonium chloride to create an interaction with the prevalent defect sites, specifically the halide vacancies in the cubic phase FAPbI3. This integration led to improvements in structural integrity and carrier dynamics, resulting in an impressive carrier lifetime exceeding 18 microseconds. The solar cells achieved a PCE of 24.13%, while a module demonstrated a PCE of 21.92% (with a certified efficiency of 21.44%) and showed prolonged operational stability.
The researchers believe that the 3C/6H hetero-polytypic perovskite configuration represents an ideal model for polycrystalline perovskite films. Their work illustrates that engineering defects in perovskite materials can significantly propel the development of high-performance solar cells suitable for various applications, including rooftop installations, portable electronics, and mobile chargers.
“Perovskite solar cells provide a revolutionary approach toward achieving carbon neutrality and tackling climate change. Their high efficiency, adaptability, and minimal environmental impact position them as crucial elements in the transition to sustainable energy solutions,” concluded Prof. Kim.
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