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Information Center for Mathematical Science

세미나

Information Center for Mathematical Science

세미나

KAIST 화학과 세미나
Title Carrier Dynamics at Organic Material Interfaces
Date 2018-08-29
Speaker Dr Jeong Won Kim(KRISS)
Sponsors 2018-08-29
Host KAIST
Place #1501(E6-1)
Abstract Among fundamental issues in photophysics and photochemistry, charge generation and separation/recombination at material interfaces are a primarily important problem to be studied for high efficiency in photovoltaic application. Organic/inorganic hybrid solar cell (HSC) is one of the future generation photovoltaics where the charge separation takes place near the heterointerface. To unveil physical behavior of hybrid “Frenkel-Wannier exciton” at the organic/inorganic hybrid interface, I focus on a typical semiconducting material combination, gallium arsenide (GaAs) as inorganic absorber and copper phthalocyanine (CuPc) as organic counterpart. Ultrafast charge transport and separation dynamics are studied by using time-resolved two-photon photoemission spectroscopy (TR-2PPE). CuPc/p-GaAs shows hole injection behavior depending on light intensity [1]. In addition, the photo-generated carriers within GaAs exhibit a few different pathways of relaxation and transfer on picosecond time scale time. At the CuPc/p-GaAs interface, a “hybrid charge transfer exciton (HCTE) state” [2] evolves right after the hole injection from GaAs to CuPc. The initial HCTE state splits into relaxed HCTE states and triplet state (T1) in CuPc. The formation of T1 may be applied to a low power LED if the relaxation to HCTE states is blocked [3]. As another example of organic solar cell devices, we compare electron dynamics of ZnPc/C60 and CuPc/C60 interfaces. Control of CuPc molecular plane into lying-down orientation enhances charge separation and interface charge transfer exciton formation. However, actual solar cell performance is influenced largely by charge mobility and crystallinity of the molecules.