A new passivation process, developed by researchers in South Korea, for formamidinium lead iodide (FAPbI3) perovskite films offers certified 24.13% power conversion efficiency in solar cells, according to their demonstration.
The research team led by Professor Hobeom Kim from the Gwangju Institute of Science and Technology (GIST) developed the new defect passivation strategy. The process significantly reduces defects and improves power conversion efficiency and stability of perovskite solar cells.
Researchers reported introducing hexagonal polytype (6H) [different structural forms with the same composition] perovskite into the cubic polytype (3C) FAPbI3, which led to a remarkable increase in their PCE when compared to their counterparts.
FAPbI3 suffers from defects in its crystalline structure
Polycrystalline formamidinium lead iodide (FAPbI3), widely used for making perovskite-based solar cells due to its superior optoelectronic properties, suffers from defects in its crystalline structure.
Researchers from the Gwangju Institute of Science and Technology (GIST) introduced hexagonal polytype perovskite (6H) into the cubic polytype (3C) FAPbI3 to reduce these defects, which led to improved power conversion efficiency and operational stability of perovskite solar cells, when compared with their existing counterparts, according to their study .
Researchers employ a chemically identical polytype of perovskite
“A typical approach so far has been to introduce an external chemical reagent to deal with the defect problem,” said Prof. Kim.
“However, bringing in external reagents could directly impact the crystalline quality of the perovskite during crystal growth, so our work does not rely on such stabilizers. Instead, we employ a chemically identical polytype of perovskite, 6H polytype containing a corner-sharing component that effectively suppresses the formation of defects in perovskite.”
The study published in the journal Nature incorporated 6H perovskite into FAPbI3, by using excess of lead iodide and methylammonium chloride, thereby creating a component that intervened with the dominant defect site (halide vacancies, VI+) of α-phase cubic polytype (3C) FAPbI3.
6H phase improved structural integrity and carrier dynamics of FAPbI3
Researchers found that the 6H phase improved the structural integrity and carrier dynamics of FAPbI3. This led to an ultralong carrier lifetime of greater than 18 microseconds, PSCs with PCEs of 24.13% and a module with PCEs of 21.92% (certified power conversion efficiency of 21.44%) with long-term operational stability.
The study also suggested that the 3C/6H hetero-polytypic perovskite design might be the closest to the ideal configuration of a polycrystalline perovskite film.
The study demonstrated how engineering defects in perovskite can accelerate the development of advanced PSCs for personal and commercial uses, such as in rooftop solar panels, wearable electronics, and portable chargers, according to a press release by GIST.
Prof. Kim stated that perovskite solar cells offer a transformative solution for achieving carbon neutrality and addressing global warming. Their efficiency, versatility, and reduced environmental impact make them an essential component in the transition to a sustainable future, according to Kim.
Additional surface passivation on top of the hetero-polytypic perovskite film results in an ultra-long carrier lifetime exceeding 18 μs, affords power conversion efficiencies of 24.13% for perovskite solar cells, 21.92% (certified power conversion efficiency: 21.44%) for a module, and long-term stability, according to the study titled “Shallow-level defect passivation by 6H perovskite polytype for highly efficient and stable perovskite solar cells.”
The hetero-polytypic perovskite configuration may be considered as close to the ideal polycrystalline structure in terms of charge carrier dynamics and stability, according to researchers.
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