Higher surface uniformity makes for a better perovskite solar cell

Perovskites are one of the most promising photovoltaic materials for solar energy due to their high efficiency. The search to stabilize and retain high efficiencies in perovskite solar cells remains a major hurdle for practical applications.

Using a combination of synchrotron X-ray techniques, Li et al. studied the surface properties of perovskite solar cells and their relationship with performance. With optical and electronic characterizations, they found in general that a higher surface uniformity results in better performing perovskite films.

“This is the first study that experimentally correlates the perovskite thin film morphology and carbon heterogeneity with device function,” said author Feng Liu.

The authors used X-ray photoemission electron microscopy and X-ray diffraction to measure the surface chemistry and crystal structure of methylammonium lead triiodide perovskite films.

The measurements showed how different preparation methods affect local surface chemistry. The grain boundaries of the solvent annealed films were carbon rich, whereas the grain boundaries of the thermally annealed control film featured carbon-related contaminants.

The authors attribute the underlying mechanism of this difference to a liquid-like intermediate phase during solvent annealing, which reduces lattice strain and causes carbon species to gather at the grain boundary area. Since carbon homogeneity improves the photophysical responses in perovskite thin films, the authors emphasize the importance of controlling the local chemistry when fabricating high-performing, stable perovskite-based devices.

“This work provides a useful methodology to study the composition variation and morphology in perovskite solar cells,” Wang said. “It can be applied to study the surface passivation effect or other systems where composition and morphology come into play.”

Source: “Surface and grain boundary carbon heterogeneity in CH₃NH₃PbI₃ perovskites and its impact on optoelectronic properties,” by Yu Li, Qin Hu, Peijian Wang, Rajesh Chopdekar, Andreas Scholl, Zhe Zhao, Yecheng Zou, M. Iqbal Bakti Utama, Feng Wang, Michael Barnes, Yongming Zhang, Thomas P. Russell, and Feng Liu, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/5.0023701 .