Over the years, with the help of advanced technology and research, hybrid organic-inorganic perovskites have come under the spotlight owing to their superior property profile and the tailorability of their structure ranging from 0D to 3D. This opens avenues for these hybrid perovskites to be utilized in any critical applications such as polarized photodetectors, light-emitting diodes, and even spintronic devices. What makes these compounds unique is the chiroptical property related to their property profile. This chirality allows these compounds to have an inherent non-centrosymmetric and a polar structure that helps enhance their property profile in avenues of forming a unique crystal structure and amplifying its ferroelectric and non-linear optic (NLO) properties. There remains a challenge, however, to formulate such a crystal structure that has good optical transparency and hence physical and chemical properties. The researchers aim to make a hybrid perovskite that has a good NLO coefficient and is strong under different optical situations.
Dr. Zheng Yongshen and Dr. Xian-He Bu under the supervision of professor Dr. Jialiang Xu manufactured these hybrid perovskite crystals and films. The research team developed new method to form the hybrid perovskite single crystals. The precursor compounds (ammine, methanol, and hydrobromic acid) were treated to form these crystals with the help of processes such as rotary evaporation. Further compounds were added to formulate the desired product. These single crystals were also made into films with the help of a spin-coating method which utilized a specific substrate onto which the films were deposited. Examination of these crystals to find out their property profile was done via a microscope and other compounds such as urea crystals. The original research article is now published in Journal of Advanced Optical Materials.
The researchers were able to carry out proper testing on these crystals and films to identify important properties such as linear optical, chiroptical, nonlinear optical, NLO, and second harmonic generation (SHG). The crystal formed exhibited a very well-shaped structure that was confirmed with the help of high-resolution imagery. These crystals also showed impressive properties with respect to thermal and air stabilities. The film and crystal after careful testing showed excellent SHG properties along with high transparency, polarization ratio, and laser damage threshold and maintained their structure in the air and thermal tests as mentioned earlier.
The research team were able to identify PbBr3 crystals as a key candidate to be utilized in many NLO applications by virtue of their property profile. The crystal formed was able to have a very high SHG response (572 times of quartz at 980nm) that was much better than the researcher’s previous work and more importantly was much better than other hybrid perovskites. For this result, the crystal was subjected to a wavelength-dependent spectrum in the range of 800-1020nm which showed an immense response at 980 nm. According to the authors that this value was much higher than any SHG response they might know in their knowledge. This creates a breakthrough for PbBr3 to be utilized in these NLO applications.
In conclusion, the researchers developed a hybrid perovskite that could enhance the electrical devices market. They formed a PbBr3 crystal that was subjected to different tests for its linear and nonlinear properties. The structure formed was 1D which had a smooth surface with diffraction spots and high-resolution imagery showed that the lattice spacing in the structure was close to its theoretical value. The crystal also showed excellent stability toward laser power attack that was much higher than the researchers expected hence exhibiting its exceptional property profile. The way this compound behaved clearly opens the avenue for much more advanced research in this field to form hybrid perovskites for high-performance second-order NLO properties.
Y. Zheng, J. Xu, and X. Bu, “1D Chiral Lead Halide Perovskites with Superior Second‐Order Optical Nonlinearity”, Advanced Optical Materials, vol. 10, no. 1, p. 2101545, 2021.