태양 전지용 CuInSe₂ 단결정 박막 성장과 태양 전지로의 응용

Abstract

The stoichiometric mixture of evaporating materials for the CuInSe₂ single crystal thin film was prepared from horizontal furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal CuInSe₂, it was found tetragonal structure whose lattice constant a0 and c0 were 5.783 Å and 11.621 Å, respectively. To obtain the CuInSe₂ single crystal thin film , CuInSe₂ mixed crystal was deposited on throughly etched GaAs(100) by the hot wall epitaxy(HWE) system. The source and substrate temperature were 620 ℃ and 410 ℃ respectively. The crystalline structure of CuInSe₂ single crystal thin film was investigated by the double crystal X-ray diffraction. Hall effect on this sample was measured by the method of van der Pauw and studied on carrier density and mobility depending on temperature. From Hall data, the mobility was likely to be decreased by impurity scattering in the temperature range 30 K to 100 K and by lattice scattering in the temperature range 100 K to 293 K. The temperature dependence of the energy band gap of the CuInSe₂ obtained from the absorption spectra was well described by the Varshni's relation, E_(g)(T) = 1.1851 eV - (8.99 × 10^(-4) eV/K)T²/(T + 153 K). The crystal field and the spin-orbit splitting energies for the valence band of the CuInSe₂ have been estimated to be 0.0087 eV and 0.2329 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ7 states of the valence band of the CuInSe₂. The three photocurrent peaks observed at 10K are ascribed to the A₁-, B₁-, and C₁-exciton peaks for n = 1. From the photoluminescence measurement of CuInSe₂ single crystal thin film , we observed free excition (Ex) observable only in high quality crystal and neutral acceptor-bound exciton (A˚,X) having very strong peak intensity. And, the full width at half maximum and binding energy of neutral accepor bound excition were 7.0 meV and 5.9 meV, respectively. By Haynes rule, an activation energy of impurity was 59 meV. The open-circuit voltage, short current density, fill factor and conversion efficiency of n-CdS/p-CuInSe₂ heterojunction solar cells under 80 mW/cm² illumination were found to be 0.51 V, 29.3 mA/cm², 0.76 and 14.3 % respectively.