Hyuk-Ryeol Park

Photovoltaic characteristics of CuInS2CdS solar cell by electron beam evaporation

When a CuInS2CdS solar cell was fabricated by depositing CdS thin film with dopant In of 1.0 at% on ternary compound CuInS2 thin film with the lowest resistivity of 5.59 × 10−2 Ωcm, its best result was as follows: Voc = 461 mV, Isc = 26.9 mA, FF = 0.685, η = 5.66% under the illumination of 100 mW/cm2. And its series resistance and lattice mismatch was 5.1 Ω and 3.2%, respectively. Besides, a 4 layer structure solar cell of ϱ-CuInS2/high ϱ-CuInS2/high ϱ-CdS/low ϱ - CdS has been fabricated. When thickness of high ϱ - CuInS2 was 0.2 μm, its best result was as follows: Voc = 580 mV, Isc = 30.6 mA, FF = 0.697, η = 8.25%. An its series resistance and lattice mismatch were 4.3 Ω and 2.8%, respectively.

Change in bulk defect density of hydrogenated amorphous silicon by bias stress in thin film transistor structures

The changes in defect density of hydrogenated amorphous silicon (a‐Si:H) in thin film transistor (TFT) structures by prolonged bias stress or light soaking have been studied through constant photocurrent method (CPM) measurements. The CPM absorptions due to defect absorptions do not change after positive or negative bias‐stress. On the other hand, the CPM absorptions due to dangling bond defects increase remarkably after light soaking. These experimental results demonstrate that the bulk defect density of a‐Si:H in TFT structure is not changed after long time bias stress even though the characteristics of the TFT degrade significantly.

Optical absorption spectra of a-Si : H films in TFT structure

Abstract The a.c. constant photocurrent method (CPM) was applied to measure optical absorption spectra of hydrogenated amorphous silicon (a-Si : H) films in thin-film transistor (TFT) structure. Specifically, the behavior of CPM spectra with gate voltage was investigated to learn the influence of band-bending on the CPM spectra. The observed spectra show a reduced defect absorption when band-bending (either upward or downward) is formed at the silicon-insulator interface. The results are explained by the changed dangling bond states by band-bending in a-Si : H near the interface.

Characterization of the hole capacitance of hydrogenated amorphous silicon metal–insulator–semiconductor structures

The capatiance–voltage characteristics associated with the hole accumulation in hydrogenated amorphous silicon metal–insulator–semiconductor structures were investigated. The capacitance was measured by using an ac voltage and a quasistatic method. In the ac measurements, we observed the partial response of the hole capacitance, while the full response of the hole capacitance was confirmed by quasi-static measurements. The effect of illumination on the hole capacitance was also investigated. One possible mechanism accounting for the frequency and temperature dependencies of the hole capacitance is proposed.

Light-induced defect generation in hydrogenated amorphous silicon under the constant photocurrent conditions

Abstract We measured the decay of the steady state photoconductivity in a -Si : H due to light soaking under the constant photocurrent condition, in which the light intensity was increased to keep the photocurrent constant and the photoconductivity was measured at a preset light intensity. The results are discussed in terms of the Stutzmanns model and the model of Redfield and Bube. We have found that Redfield and Bubes equation in a modified form including carrier enhanced dispersion may be used to describe light-induced defect generation.

Dependence of the saturated light-induced photoconductivity on macroscopic properties of hydrogenated amorphous silicon

Abstract We have investigated the saturated light-induced photoconductivity σph,sat in 37 hydrogenated (and in part fluorinated) amorphous silicon [a-Si:H(F)] films grown in six different reactors under widely different conditions. σph,sat was attained by exposing the films to light from a krypton ion laser (λ = 647.1 nm). σph,sat, determined at an average carrier generation rate of G = (5.0 ± 1.0) × 1020 cm−3 s−1, lies between 2.3 × 10−6 and 2.0 × 10−8 S cm−1. σph,sat have more explicit correlation with the optical gap Eopt than the Urbach tail energy Eu. σph,sat increase with decreasing Eopt and hydrogen content cH. We discussed our results within the framework of existing models for light-induced defects.

Light-induced defect generation of a-Si: H at below-room-temperature

Abstract We report new experimental results on the behavior of the light- induced defect generation of a -Si: H at below-room-temperature. Light-soaking of well characterized hydrogenated (and fluorinated) amorphous silicon was carried out under constant illumination at the temperature range of 305–350 K. Light-induced defects are generated even at far below-room-temperature, although the amount is less. The experimental data on defect density as a function of light-soaking time can be described with the streched exponential by adjusting the values of both dispersion parameter β and time constant τ. Light-induced defect generation has a weak temperature dependence at below-room- temperature. We discuss our results within the framework of existing models for light-induced defects.