Hong Kong University of Science and Technology (HKUST) researchers have gained insights into perovskite microstructure. After removing grain surface concavities in the crystalline grains of perovskite, they fabricated a solar cell with improved efficiency retention under standardized thermal cycling, damp heat, and maximum-power-point tracking tests.

Scientists from the School of Engineering of the  HKUST have revealed the existence and impact of surface concavities on individual crystal grains of perovskite thin films.

They claimed in “Elimination of Grain Surface Concavities for Improved Perovskite Thin-Film Interfaces” – recently published in Nature Energy – that the concavities in perovskite materials are “triggered by grain-coalescence-induced biaxial tensile strain and thermal-coarsening-induced grain-boundary grooving.”

The scientists said the concavities break the structural continuity at the perovskite film interface and limit the efficiency and stability of perovskite cells. A statement from HKUST explained that while perovskite solar cells have the potential to replace existing silicon cells in many applications, their long-term stability under light, humidity, and thermomechanical conditions remains a barrier to commercialization.

To fully explore the impact of the grain surface concavities, the team removed them by using a surfactant molecule, tridecafluorohexane-1-sulfonic acid potassium, to manipulate the strain evolution and ion diffusion during the formation of perovskite films.

In the research paper, the researchers document how their resultant perovskite solar cells demonstrated enhanced power conversion efficiency and elevated power conversion efficiency retention under ISOS-standardized thermal cycling (300 cycles), damp heat (660 hours) and maximum power point tracking (1,290 hours) tests.

“Structure and geometry of individual crystalline grains are the origin of the performance of perovskite semiconductors and solar cells,” said Prof. Zhou Yuanyuan, the corresponding author of the research paper. “By unveiling the grain surface concavities, understanding their effects, and leveraging chemical engineering to tailor their geometry, we are pioneering a new way of making perovskite solar cells with efficiency and stability toward their limits.”

Zhou said the team was “intrigued by the surface concavities of perovskite grains” observed through atomic force microscopy, as concavities are typically hidden beneath the film bottom and are often overlooked.