Researchers from the University of Sydney and Shanghai Jiao Tong University have combined first-principles calculations and machine learning molecular dynamics to examine the interplay between perovskite octahedral lattice dynamics and energy barrier associated with ion migration.
Image from: Science Advances
The team reported suppressed ion migration in halide perovskites specifically at the B-site, opening the door to cell stabilization by minimizing energy loss and improving performance reliability.
The recent paper shows changing certain atoms in halide perovskites, specifically at the B-site, can make them more stable by strengthening interactions between atoms, reducing how much the structure moves and minimizing migration of ions. It was discovered that adding elements like alkaline-earth metals, such as calcium (Ca) or lanthanides (rare earth metals) such as europium (Eu) and Ytterbium (Yb) to the B-site was especially effective.
Lead halide perovskites tend to suffer issues with long-term stability, in part due to ion migration that negatively affects their performance. The study says that despite achieving a photovoltaic power conversion efficiency exceeding 26%, halide perovskite commercialization is largely hindered by inadequate long-term operational stability.
“One of the main drivers for this instability is ion migration, typically halide ions, which has been identified as a major cause of device performance degradation under operational conditions with electric field, light, and heat,” the paper says.
“These mobile ions in the perovskite active layer are believed to be responsible for widely observed anomalies, such as current-voltage hysteresis, slow conductivity response, and efficiency roll-off at high injection currents.”
Experiments have shown that ion migration–induced internal field screening is the dominant factor in the initial efficiency loss in perovskite solar cells making suppression of ion migration crucial to achieving long-term operational stability in perovskite solar cells and other optoelectronic devices.
Strain and compositional engineering strategies have been adopted to alleviate the migration of halide ions, in particular, the ternary-stoichiometry ABX3 perovskite structure offers a highly flexible platform for doping engineering at different atomic sites.
“While layer-perovskite engineering with large spacer cations effectively blocks ion migration, it disrupts the three-dimensional (3D) phases, leading to reduced charge carrier mobility and narrower absorption bands, thereby limiting the photovoltaic efficiency,” the researchers say.
“B-site doping or alloying has been less explored due to its relatively higher formation energy, with a primary focus only on carbon group elements such as germanium (Ge), tin (Sn), and lead (Pb).”
“Notably, the wider variety of potential dopants, such as rare earth ions, alkaline earth metal ions, and transition metal ions, establishes B-site cation engineering as a promising avenue for effectively suppressing ion migration and improving the long-term stability of perovskites optoelectronics,” the paper says.
