- 건국대학교

	Prof. Man-Jong Lee reported an innovative synthesis process and solved one of the unresolved problems in perovskite solar cells
	관리자		476		2018.11.16

Prof. Man-Jong Lee reported an innovative synthesis process and solved one of the unresolved problems in perovskite solar cells. Journal published in the prestigious SCI journal of NANO ENERGY (impact factor: 13.120) <img style="margin-left: auto; display: block; margin-right: auto;" alt="" src="ArticleFile.do?id=11748520" /> Prof. Man-Jong Lee (Department of Chemistry), Konkuk University, presented a new innovative fabrication technique for the fabrication of perovskite solar cells (PSCs) which show a growing attention as a next-generation solar cell. Through this method, he solved a difficult issue that was not solved so far. These results are published online (October 15, 2018) in the top international journal of 'Nano Energy' (impact factor 13.120) (<a href="https://doi.org/10.1016/j.nanoen.2018.10.023">https://doi.org/10.1016/j.nanoen.2018.10.023</a>). 
PSCs recently achieved a high photovoltaic power conversion efficiency over 22% and has the advantages of a simple/inexpensive manufacturing method including the spin coating process of a precursor solution. Therefore, worldwide research efforts are now focused on actual commercialization. Although the chemical coating process is a simple method for the synthesis of PSCs at room temperature and atmospheric pressure, there are some process difficulties. The conventional coating method for perovskite films uses a 'static spin process' in which a perovskite precursor solution is temporarily loaded on a substrate to spin-coat perovskite layer. In this process, the rapid evaporation of the volatile solvents in the precursor solution caused the formation of various pinholes or defects in the microstructure of perovskite absorber layer, thereby reducing the efficiencies. To solve this problem, an additional complex solvent washing process is necessary, which makes the whole processes complex. 
 Based on the crystal growth theories that the continuous dropping of a solution can result in a better microstructure, Prof. Lee proposed a new innovative process termed 'dynamic spin coating process' in which the mixed perovskite precursor solution is continuously loaded during the coating process. Using this technique, he demonstrated that a defect-free perovskite absorber layer can be successfully synthesized without an aid of additional solvent washing process (Fig. 1). In addition, when the spin coating process is repeated, spontaneous ion exchange of the perovskite solution becomes possible, and the final compositions of the double-perovskite can be modified even with the initial solution of a constant concentration (Fig. 1). A solar cell manufacturing method with excellent efficiency and stability is achieved through the fine control of spontaneous ion exchange process (Fig. 2). 
 Developing a new perovskite composition or achieving the world's best efficiencies are important research goals in PSC research society. On the other hand, there are still many research problems to be solved for highly efficient and stable PSCs. One of them is the stoichiometric control of the perovskite phase; it is very difficult to precisely match the stoichiometry of the perovskite phase prepared by the solution method. Of course, for high efficiency, the exactly matched stoichiometry might not be the best solution, but there is no report on the studies of methyl group (CH3 related) or ammonium group (NH3 related) cations which may exist as excess ions on perovskite produced by solution method. Prof. Lee's group first applied the two-dimensional Fourier transform infrared spectroscopy (FTIR) imaging technique and showed that the perovskite phases produced under the excess cation environment show non-stoichiometric compositions by adsorbing excess cations on the surfaces. Experiments also demonstrated that cations adversely affect the efficiency (Fig. 2 and 3). 
Professor Lee said, “The study is remarkable in that a new innovative process is introduced which reduces the process complexity of perovskite solar cells and that a well-known difficult issue on the detection of excess residual cations and their influences on the properties have been solved.” 
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT. This research was also supported by the Agency for Defense Development (ADD) of the Republic of Korea through the university research center program. <img style="margin-left: auto; display: block; margin-right: auto;" alt="" src="ArticleFile.do?id=11748519" width="533" height="329" />                               Figure 1. Dynamic spin coating technique and spontaneous cation exchange
 <img style="margin-left: auto; display: block; margin-right: auto;" alt="" src="ArticleFile.do?id=11748522" width="486" height="355" /> 
Fig. 2. (a) Cross-sectional area of a full cell fabricated by the dynamic spin coating process, (b) photovoltaic efficiency, (c) quantum efficiencies, and (d) hysteresis and stability <img alt="" src="ArticleFile.do?id=11748523" width="566" height="306" /> 
Fig. 3. Charge transfer rate and excess cation analysis using fluorescence (PL) imaging and two-dimensional Fourier transform infrared spectroscopy (FTIR) imaging.

	사진_1.JPG (33,271) 사진_2.JPG (42,437) 사진_3.JPG (40,042) 사진_4.JPG (39,271)
	Prof. Yongseok Jun and his te...
	Prof. Man-Jong Lee presented ...