(a) Schematic of the PEAI-treated FAPI film preparation. b) Schematic of the hypothesized structure at the surface and in the bulk after PEAI deposition onto 3D FAPI perovskites. (c) Solar cell device architecture. Reproduced from: Hidalgo et al., Materials Today (2023), https://doi.org/10.1016/j.mattod.2023.06.010.
Photograph of a PEAI-treated FAPI film PSC. Credit: Lahoucine Atourki.Low-cost, high-efficiency perovskite solar cells (PSCs) are a promising renewable energy technology but degrade when exposed to air and moisture. To overcome this limitation, lead halide perovskites can be treated with certain types of cations.
Now a team from Georgia Institute of Technology, Brookhaven National Laboratory, Wesleyan University, Florida State University, and Mohammed V University in Rabat have investigated in detail how the cation phenethylammonium iodide (PEAI) interacts with the perovskite formamidinium lead iodide (FAPI) [Hidalgo et al., Materials Today (2023), https://doi.org/10.1016/j.mattod.2023.06.010 ].
“We hypothesized that the addition of the bulky PEAI cation to a particular perovskite material, FAPI, could improve stability and efficiency,” explains Lahoucine Atourki.
The researchers fabricated thin films of the perovskite FAPI and added a layer of PEAI on top to create a capping layer. No other additives were used. Using a variety of advanced characterization techniques, including grazing-incidence wide-angle X-ray scattering (GISWAS), time-resolved photoluminescence (TRPL), and terahertz spectroscopy, the team investigated the structural and optoelectronic properties of the perovskite with and without the capping layer.
“These analyses allowed us to understand how the PEAI cation interacts with the FAPI perovskite and how it affects its stability and performance,” points out Atourki.
The capping layer improves the stability of the FAPI perovskite by reducing surface exposure to air and light, which causes degradation. The bulky cation appears to reduce the formation of non-perovskite hexagonal phases, which are linked to poor optoelectronic properties, reduced device performance, and decreased stability. The PEAI cation also enhances carrier lifetime and photoconductivity by reducing non-radiative recombination, thereby boosting power conversion efficiencies (PCEs). Solar cells based on the PEAI-coated FAPI perovskite demonstrate PCEs of up to 20.2% and open circuit voltages (Voc) of up to 1.14 V, which are among the highest values reported to date for this type of device.
“The findings from this research hold several practical applications,” says Atourki. “The PEAI capping layer alone could lead to substantial improvements in stability and efficiency, offering a simplified and effective approach to enhance perovskite solar cells.”
As well as making PSCs more viable with longer operational lifetimes, the boost to efficiency potentially renders the technology more competitive and attractive for real-world renewable energy applications.
“The insights gained from this study could also guide further research into optimizing other perovskite materials and their interactions with different cations for even better performance,” adds Atourki.