Researchers have unveiled a new strategy for defect passivation aimed at enhancing the efficiency and stability of perovskite solar cells.
Polycrystalline formamidinium lead iodide (FAPbI3) is a widely accepted material in the production of perovskite solar cells due to its excellent optoelectronic characteristics, though it faces issues related to defects in its crystal structure. A team from the Gwangju Institute of Science and Technology (GIST) has introduced a hexagonal polytype perovskite (6H) into the cubic variant (3C) of FAPbI3 to mitigate these defects, resulting in enhanced power conversion efficiency and stability compared to current models.
Utilizing solar energy is a promising method for reducing reliance on fossil fuels and embracing cleaner energy solutions. Over time, advancements in solar cell technology have considerably improved our ability to capture this renewable energy.
Metal-halide perovskites have emerged as an attractive option for solar cells due to their remarkable ability to absorb light and convert it into energy effectively.
Among these, polycrystalline formamidinium lead iodide (FAPbI3) is a highly favored material for high-power conversion efficiency (PCE) perovskite solar cells (PSCs), owing to its narrow energy band gap. However, despite its excellent optoelectronic properties, materials like FAPbI3 frequently experience defects in their crystalline structure. These imperfections negatively impact the stability and carrier dynamics of the material, thus undermining energy conversion efficiency.
Addressing these issues, a group of researchers led by Professor Hobeom Kim at the Gwangju Institute of Science and Technology (GIST) has devised a novel defect passivation strategy. This method effectively diminishes defects, thus enhancing PCE and the stability of perovskite solar cells. Their findings, published on July 4, 2024, in Nature Communications, reveal that integrating hexagonal polytype (6H) perovskite into cubic polytype (3C) FAPbI3 significantly boosts PCE compared to alternative approaches.
So, why the choice of 6H perovskite polytype? Professor Kim explains, “Traditionally, researchers introduced external chemical agents to counteract the defect issues, but these could adversely affect crystal quality during growth. Our approach, however, uses an internally compatible polytype, specifically the 6H variant, which features a corner-sharing structure that effectively reduces defect formation.”
The research team achieved this incorporation by adding extra lead iodide and methylammonium chloride, creating a component that interacts with the prevalent defect sites (halide vacancies, VI+) in the α-phase cubic polytype (3C) FAPbI3. Their results showed that the presence of the 6H phase significantly enhanced the structural stability and carrier dynamics of FAPbI3. This led to an impressive carrier lifetime exceeding 18 microseconds, along with PSCs reaching PCEs of 24.13% and a module with PCEs of 21.92% (with a certified efficiency of 21.44%) while ensuring long-term stability during operation.
The researchers propose that the design combining 3C and 6H perovskites may offer an optimal configuration for polycrystalline perovskite films. Their research illustrates how modifying defects in perovskite materials can propel the advancement of PSCs for both personal and commercial applications, including rooftop solar installations, wearable electronics, and portable charging solutions.
Professor Kim concluded, “Perovskite solar cells present a groundbreaking opportunity to achieve carbon neutrality and tackle climate change. Their efficiency, adaptability, and minimal environmental impact make them crucial for the transition towards a sustainable future.”
