Zhu Rui and Gong Qihuang research group of the School of Physics have made new progress in full-scale grain boundary optimization of perovskite solar cells

Polycrystalline halide perovskite materials have become cutting-edge hot materials
in the research fields of solar cells, light-emitting diodes, lasers and photodetectors due to their easy preparation and excellent photoelectric properties.
Typically, perovskite films are rapidly nucleated and crystallized from solution at relatively low temperatures, which results in a complex polycrystalline structure of perovskite films with a large number of grain boundaries
.
A polycrystalline is a collection of grains of different orientations, one grain is a single crystal solid, and the grain boundary is the interface
between adjacent grains of different orientations within the same material.
Grain aggregation is widespread within polycrystalline thin films, and grain aggregates will further grow to form larger particles, eventually creating an inter-grain aggregate interface [which is often inappropriately referred to as "grain boundaries" in the field of metal halide perovskite research
].
。 As shown in Figure A, the interface in a polycrystalline perovskite film can be divided into two categories: the submicron-scale "interaggregate grain boundary" and the nanoscale "intra-aggregate grain boundary", which is the real "grain boundary"
in perovskite polycrystalline films.

Schematic diagram of solid polycrystalline thin film and perovskite film morphology: A.

In metal halide perovskite materials, serious non-radiative recombination is prone to occur at the interface between grain aggregates at the submicron scale, which in turn affects carrier transport, promotes ion migration, and introduces deep energy level defects, resulting in a decrease
in the efficiency and stability of perovskite solar cells.

In view of this, Zhu Rui, a researcher at the School of Physics of Peking University, and Academician Gong Qihuang's research group and collaborators conducted in-depth research
on the structure and grain boundary regulation strategy of perovskite polycrystalline thin films.

Direct observation of the grain boundaries of perovskite grains, grain aggregates and aggregates: A.

STEM-EELS chemical composition map and GIXD results of perovskite thin films: A.

Photovoltaic performance improvement of the device: A.

Based on the above research work, the team pointed out the deviation of the cognition of "grain boundary" in the field of perovskite optoelectronic materials, and gave a clearer explanation of the real "grain boundary" in the hybrid perovskite film.

On September 2, 2022, the research results were published online in Science Advances, 8, eabo3733, 2022 under the title "Enabling full-scale grain boundary mitigation in polycrystalline perovskite solids".

The above research work has been strongly supported
by the National Natural Science Foundation of China, the Beijing Municipal Natural Science Foundation, the National Key Research and Development Program, the China Postdoctoral Science Foundation, as well as the State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, the Nanophotoelectronics Frontier Science Center, the Collaborative Innovation Center for Quantum Matter Science, the Extreme Optical Collaborative Innovation Center, and the University of Science and Technology of China.