Uneven charge losses between neighboring crystal grains contribute to light-induced degradation in perovskite solar cells
Researchers developed a grain-boundary treatment to reduce defects and improve charge balance
Treated cells achieved 26.55% efficiency and retained over 90% of their initial performance after more than 2,200 hours of continuous illumination
Researchers from the Hong Kong Polytechnic University (PolyU) and Zhejiang University have identified a new factor contributing to the degradation of perovskite solar cells under prolonged light exposure. The study links uneven charge losses between neighboring crystal grains to accelerated aging, including in regions normally considered more stable. The researchers also developed a chemical treatment that improved cell stability, with treated cells achieving 26.55% efficiency.
Perovskite solar cells can lose efficiency over time due to defects in the material that trap electrical charges. The latest study, titled Stabilizing high-efficiency perovskite solar cells by homogenizing inter-grain recombination, published in the scientific journal Watt, examines the role of interactions between neighboring crystal grains in light-induced degradation (LID).
The perovskite absorber layer contains numerous small crystals, known as grains, with different surface orientations. The researchers investigated two common orientations, (100) and (111), and identified differences in charge losses at their shared boundaries. These differences were linked to defects concentrated on the (111) side.
The defects were mainly associated with missing formamidinium (FA) ions in the crystal structure. These vacancies led to the accumulation of positively charged carriers, or holes, near the grain boundaries. As a result, the (111) grains experienced faster degradation despite their naturally higher resistance to light-induced aging.
The team used a chemical compound called 3 fluorophenylethylammonium bromide (m-F-PEABr) to reduce defects at grain boundaries. The compound remains at these boundaries rather than entering the crystal grains. Its positively charged molecular groups occupy sites left vacant by missing FA ions, helping balance charge losses between neighboring grains.
The treated cells achieved a power conversion efficiency of 26.55%. Under continuous illumination equivalent to 1 sun, they retained more than 90% of their initial efficiency after over 2,200 hours of operation. The results indicate improved resistance to light-induced degradation under laboratory conditions.
According to PolyU Assistant Professor Guang Yang, the findings suggest that reducing the overall number of defects alone may not be sufficient to address perovskite cell aging. Uneven charge losses between neighboring grains also influence stability and need to be considered when developing more durable cells.
The findings highlight the importance of grain-boundary interactions in improving perovskite solar cell stability. However, further testing under outdoor operating conditions will be needed to assess the treatment's potential for long-term solar module applications.
Earlier research by scientists at the University of California, San Diego (UC San Diego) also explored ways to reduce defects in perovskite materials, using a temporary liquid additive to improve crystal formation (see Temporary Liquid Helps Reduce Perovskite Defects).