The Advanced Materials cover illustration shows the surface of the halide perovskite structure being modified by a large organic cation. The cation diffuses through the thin film to reconstruct the surface structure. Credit: Advanced Materials
Halide perovskite solar cells have the potential to advance solar power applications due to their low cost and high performance. However, to be a viable alternative to silicon-based solar cell technologies, which remain effective after more than 25 years of use, halide perovskite cells must be made stable and reliable for long-term use. Research recently published by a team led by Georgia Institute of Technology (Georgia Tech) researchers has revealed details about the thermal instability of cation-treated halide perovskite solar cells, and yielded new information that can aid in the development of more reliable cells.
For their experiment, the research team used perovskite films to create a solar device featuring eight independent solar cells. They used synchrotron-based X-ray analysis techniques to assess the performance of the cells, both with and without cation surface treatment, and examine their cation-modified interfaces before and after prolonged thermal stress. The positively charged cations are used on halide perovskite cells in order to increase their conversion efficiency, but alter the structure at the material interface when contacting the perovskite crystal.
The researchers used X-ray photoelectron spectroscopy to measure changes in chemical composition of the solar cell samples after exposure to 100°C temperatures for a period of 40 minutes. They also used grazing-incidence X-ray scattering to characterize the crystal structures that formed on the film’s surface, allowing them to understand how the cations diffuse into the perovskite crystal lattice. To assess the effects on solar cell performance that these structural changes may have, the team utilized excitation correlation spectroscopy, exposing the samples to very fast light pulses and measuring the light intensity emitted from the film to determine how much energy is lost.
The study revealed that certain cations introduced significant instability to the films, according to first author Carlo Perini. The atomic-scale structural changes that occurred at the interface between the metal halide perovskite and organic cations, which continued to evolve under thermal stress, contributed to a meaningful loss of power conversion efficiency in the solar cells. The pace at which these structural changes occurred depended on the type of cation used, which suggests that improved engineering of the interface layer could improve the material’s stability. This research was published in Advanced Materials.
“We hope this work will compel researchers to test these interfaces at high temperatures and seek solutions to the problem of instability,” said corresponding author Juan-Pablo Correa-Baena. “This work should point scientists in the right direction, to an area where they can focus in order to build more efficient and stable solar technologies.”