Perovskite Scientists Win Nobel Prize in Chemistry

On October 4, the Royal Swedish Academy of Sciences announced the 2023 Nobel Prize in Chemistry. The Nobel Committee awarded the 2023 Nobel Prize in Chemistry to Professor Mongi G. Bavendy (Moungi G. Bawendi) of the MIT, USA. Professor Louis E. Bruce (Louis E. Brus) , Columbia University, USA, and scientist Alexei Ikimov (Alexey I. Moungi

), Nanocrystal Technologies, USA G. received his Ph.D. degree from the University of Chicago, Illinois, USA, in 1988. Professor, MIT (MIT), Cambridge, MA, USA.

Louis E. Ph. D., Columbia University, New York, USA, 1969. Professor, Columbia University, New York, USA. Ph.D. degree, Ioffe Physical-Technical Institute,

Alexei I., St. Petersburg, Russia, 1974. Among the former Nanocrystals Technology Inc.

in New York City, the Moungi G.

from the MIT of the United States, in February 2019, the efficiency of the perovskite solar cell developed by the company was certified by NREL to reach 24.2%. It became the 10th efficiency record point of perovskite solar cells;

-In September 2019, the efficiency of its developed perovskite solar cells was certified by NREL to reach 25.2%, becoming the 11th efficiency record point of perovskite solar cells;

-February 2021, Moungi G.

What is a quantum dot? In the dark, under the irradiation of ultraviolet lamp, the solution in a row of test tubes emits pure light from blue to red, which is breathtaking. So what is a quantum dot? Why do quantum dots emit such brilliant colors? Compared with a stone, a gravel is very different in volume, and its physical and chemical properties are almost the same. But things start to change when the size of the material enters the nanoscale. What

we call quantum dots, also known as semiconductor nanocrystals, are semiconductor crystal particles composed of hundreds or thousands of atoms, generally less than 20 nanometers in size. Semiconductor materials are the cornerstone of the information society, which are generally composed of crystals with repeating unit structure, and their semiconductor properties are determined by the type of repeating unit. Due to the size of quantum dots entering the nanometer scale, the number of repeating units in semiconductor nanocrystals is limited, which leads to great changes in the electronic structure of materials. Brus and Ekimov et al. Described this size-dependent phenomenon as a quantum confinement effect: the electronic structure of quantum dots changes from the continuous energy band of the bulk material (macroscopic crystal) to discrete energy levels, and the band gap gradually increases with the decrease of crystal size. At the same time, since the size of QDs is usually smaller than exciton (electron-hole pair) Bohr radius, the excitons generated by optical excitation are firmly bound in each QD, thus achieving high efficiency of radiative recombination (Fig. 2). Taking the most widely studied cadmium selenide (CdSe) quantum dots as an example, the bulk cadmium selenide is black powder, which usually has no fluorescence effect, while the cadmium selenide quantum dots synthesized in solution can achieve multi-color luminescence from blue light to red light by changing the size (Figure 1).

(2) The origin

of quantum dot research Human research on semiconductor quantum dots began about 40 years ago, by two research groups in the former Soviet Union and the United States, respectively, in " around 1980. After S. I., the former Soviet scientist Alexey I Ekimov explained the quantum size effect with the particle-in-a-box model [3] through the cooperation with theoretical physicist Alexander Efros and others on the basis of spectroscopy research. Interestingly, in order to reduce the controversy in the peer review process of academic journals in the former Soviet Union, Ekimov and Efros et al. Used the term "microcrystal" in their original paper to describe the samples they studied, ranging from micron-scale crystals close to the bulk phase to nanocrystals showing significant size dependence (the smallest sample size is close to 2.

Professor Louis Brus of Columbia University, who works at Bell Laboratories in the United States, also accidentally discovered the color change caused by the size change while studying the colloidal solution of II-VI semiconductor nanocrystals. Because of the background of the Cold War at that time, academic exchanges between the Soviet Union and the United States were interrupted by the "Iron Curtain", and Professor Brus did not have the opportunity to learn about the work of Ekimov and Efros. At that time, Brus noticed the one-dimensional confinement effect of epitaxially grown semiconductor superlattices. On this basis, based on the effective mass theory and taking into account the enhanced Coulomb interaction caused by dielectric polarization, Brus deduced the relationship between the first exciton excited state energy (E *) of quantum dots and the band gap width (Eg) of bulk materials, the size of nanocrystals (R), and the effective mass of electron holes (me, MH) [4]. That is, the famous Brus formula (Formula 1), which is included in textbooks. Then, the theory of quantum confinement effect has been successfully extended to ZnS, PbS, ZnSe and other material systems.

Although Ekimov and Brus have studied different material systems, "great minds think alike", based on their profound scientific insight, the theoretical model of quantum dot size has been preliminarily established.

(3) The development

of quantum dot synthesis chemistryQuantum dot synthesis chemistry is the basis for the vigorous development of quantum dot field: the application of modern chemical synthesis methods and ideas provides high-quality materials with diverse structures and rich properties for the whole field.

Thanks to the excellent leadership of Professor Brus and the excellent cooperative atmosphere of Bell Laboratory, the major progress of colloidal quantum dot synthesis chemistry also began in Bell Laboratory. In 1986, Louis Brus and his assistants Paul Alivisatos and Michal Steierwald started the metal-organic chemical synthesis of colloidal quantum dots. Moungi Bawendi joined the team in 1988. Later, Paul Alivisatos and Moungi Bawendi became independent PIs, joined the University of California, Berkeley, and the MIT, respectively, and initiated perhaps the two most famous research groups in the field of quantum dots, which trained many talents for the field.

Quantum dot synthesis chemistry made a breakthrough between 1990 and 1993, with the emergence of a "metal-organic-coordination solvent-high-temperature" synthesis route. This method was invented at Bell Labs and matured in Moungi Bawendi's group at MIT [5]. It uses dimethyl cadmium as cadmium source to synthesize high-quality cadmium selenide quantum dots in high temperature (about 300 degrees Celsius) and organic coordination solvent. This method is a milestone for the research of the whole quantum dot field. Moungi Bawendi shared the Nobel Prize!

This situation was broken by Professor Peng Xiaogang, a Chinese scholar, around 2000. Peng Xiaogang joined Paul Alivisatos as a postdoctoral fellow in 1994 and began independent research in the Department of Chemistry at the University of Arkansas in 1999. Based on the profound understanding of the reaction mechanism, Peng Xiaogang's research group developed a "green" synthesis route based on safe and non-toxic non-coordinating solvents using stable and readily available oxides or carboxylates as precursors [6-7]. With the development of new synthetic routes, the synthesis of quantum dots has gradually moved to laboratories all over the world and has been promoted in industry.

At the same time, the growth mechanism of quantum dots, core-shell structure engineering and surface ligand chemistry have also been widely explored by chemists. These advances in basic research have led to the gradual expansion of high-quality quantum dots from II-IV CdSe quantum dots to other types of semiconductor compounds, such as PbS quantum dots, InP quantum dots, CuInS2 quantum dots and so on .In 2015, the emergence of perovskite quantum dots broke through the limitation that quantum dots need to be synthesized at high temperature. Quantum dots can be reprecipitated in polymer matrix at room temperature or prepared in situ by taking advantage of the solubility difference caused by the ionic characteristics of perovskite, which brings new opportunities for optical applications.

Thanks to the progress of synthetic chemistry, quantum dots are still growing as a family of materials. The morphology and structure of quantum dots are increasingly regulated, and functional units with specific properties are constantly produced.

(4) The application