Scientists in the United Kingdom have used alumina oxide (Al₂O₃) nanoparticles (NPs) as an interfacial modifier at the hole transport layer (HTL) to increase the lifetime of perovskite solar cells.
The researchers said that the alumina nanoparticles significantly enhanced the lifespan and stability as revealed in tests under extreme heat and humidity replicating real-world conditions. “Our work provides new insights into an important, but hidden role played by Al2O3 NPs in perovskite solar cells as a nanoengineered interlayer that templates the structure above it,” they stated.
“Following stress tests carried out for more than 2000 h, we show that the incorporation of alumina as an interfacial modifier plays an important role in both iodine scavenging, compositional homogenization resulting in T80 lifetimes exceeding 1,300 h,” Hashini Perera, lead author of the research, told pv magazine. “In comparison, the more widely used polymer electrolyte results in devices degrading in 1/10th of this time.”
In the experiment, the group modified an HTL made of nickel(II) oxide (NiOx) and phosphonic acid called methyl-substituted carbazole (Me-4PACz) with PFN–Br and Al2O3. It found that the effect of the alumina oxide nanoparticles at the buried interface was to homogenize the electrical and electronic properties of the perovskite. It also “positively impacts” the device stability under heating in ambient conditions, according to Perera.
“The use of alumina nanoparticles leads to efficient scavenging of iodine, improved bulk electrical and surface electronic homogeneity in fresh films, which is preserved even when the films are degraded, and the formation of 2D perovskites, which act as a barrier against moisture-induced degradation,” stated the team.
The scientists compared stability under ISOS-D2I and ISOS-D2 conditions at 65 C. The stacks under comparison were as follows: glass substrate coated with indium tin oxide (ITO), a methyl-substituted carbazole (Me-4PACz) hole transport layer, then Al2O3 or PFN–Br, the perovskite absorber, a buckminsterfulleriene (C60) electron transport layer (ETL), a bathocuproine (BCP) buffer layer, and copper electrodes.
The group said it used a perovskite absorber composition known as 0.05FA0.79MA0.16Pb(I0.83Br0.17)3 with a bandgap of 1.63 eV. Device characterization and EQE measurements were completed, including UV-vis measurements, electron microscopic imaging and grain size analysis, kelvin probe force microscopy (KPFM), c-AFM measurements, plus GIWAXS, and XPS measurements
The findings are detailed in “Improved stability and electronic homogeneity in perovskite solar cells via a nanoengineered buried oxide interlayer,” recently published in EES Solar. “This work points towards the importance of homogenizing the optoelectronic properties of the perovskite to improve the stability of this exciting technology and carefully tailored oxide nanoparticles can aid in this,” said Perera.
The research was completed by scientists from the University of Surrey, the University of Sheffield, and the U.K. National Physical Laboratory.
Upcoming research would incorporate the strategy in larger devices. “We believe our approach has a beneficial impact on a number of perovskite absorbers, including both wide bandgap and narrow bandgap compositions, and device architectures ranging from single to multijunction architectures,” said Perera.
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