Photoluminescence of Band Gap States in AgInS2 Nanoparticles & Band Gap Grading of Cu(In,Ga)S2 Thin-Film Solar Cells

조회수 : 400 등록일 : 2015.05.11 16:29

일시 : 2015.05.13 17:00
소속 : 경희대학교 화학과
발표자 : 송재규
장소 : R404
AgInS2 nanoparticles of various sizes were synthesized over a range of reaction temperature from 120 to 180 oC. The band gap energies, obtained directly from photoluminescence spectra for the first time, were well correlated to the quantum confinement effects as a function of nanoparticle size, because the band gap shift was explained by the finite-depth-well effective mass approximation. The chalcopyrite and orthorhombic phases were observed to coexist in the AgInS2 nanoparticles, although the relative population of each phase depended on the reaction temperature and time. The band gap shift of each phase was comparable, which revealed that the size was the major determinant of the change in the band gap energy. The photodynamics of the band gap states exhibited emission-wavelength dependence, which further supported the coexistence of the two phases. The contributions of each phase in the time profiles matched the relative population of each phase observed in the steady-state photoluminescence spectra.
In addition, the photophysical properties of CuInxGa1-xS2 (CIGS) thin films, prepared by solution-based coating methods, are investigated to understand the correlation between the optical properties of these films and the electrical characteristics of solar cells fabricated using these films. Photophysical properties, such as the depth-dependent band gap and carrier lifetime, turn out to be at play in determining the energy conversion efficiency of solar cells. A double grading of the band gap in CIGS films enhances solar cell efficiency, even when defect states disturb carrier collection by non-radiative decay. The combinational stacking of different density films leads to improved solar cell performance as well as efficient fabrication because a graded band gap and reduced shunt current increase carrier collection efficiency. The photodynamics of minority-carriers suggests that the suppression of defect states is a primary area of improvement in CIGS thin films prepared by solution-based methods
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