Researchers at Hong Kong Baptist University, The Hong Kong University of Science and Technology (HKUST) and Yale University have revealed the existence of surface concavities on individual crystal grains that are the fundamental blocks of perovskite thin films, and examined their significant effects on the film properties and reliability.
Based on this discovery, the team designed a new way of making perovskite solar cells (PSCs) more efficient and stable via a chemo-elimination of these grain surface concavities.
To address the known issue of PSCs' stability, Prof. Zhou Yuanyuan, Associate Professor of the Department of Chemical and Biological Engineering at HKUST, along with the rest of the research group, discovered the proliferation of surface concavities at the crystalline grains of the perovskite material that are shown to break the structural continuity at the perovskite film interface, serving as a hidden microstructure factor limiting the efficiency and stability of perovskite cells.
Then, the team took steps to remove the grain surface concavities by using a surfactant molecule, tridecafluorohexane-1-sulfonic acid potassium, to manipulate the strain evolution and ion diffusion during the formation of perovskite films. Accordingly, their final perovskite cells demonstrated obvious improvements in efficiency retention under standardized thermal cycling, damp heat, and maximum-power-point tracking tests.
“Structure and geometry of individual crystalline grains are the origin of the performance of perovskite semiconductors and solar cells. 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,” said Prof. Zhou.
“We were very intrigued by the surface concavities of perovskite grains when we were using atomic force microscopy to examine the structural details of perovskite films. These concavities are usually buried underneath the film bottom and easily be overlooked,” he added.
“Microstructure is of vital importance for perovskite solar cells and other optoelectronic devices, and can be more complex than conventional materials owing to the hybrid organic-inorganic characteristics of perovskite materials. Under Prof. Zhou’s guidance, we are able to develop various novel characterization and data science approaches to gain insights into perovskite microstructure,” said Zhang Yalan, a PhD student in Prof. Zhou’s research group and a co-author of this work.
