Papers by Author: Byung Tae Ahn

Abstract: This study reported the fabrication of tin oxide (SnO2) nanostructures on Co-coated Si substrates by the thermal heating of Sn powders. The microstructures and morphologies of the resultant nanostructures were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM). The product mainly comprised the tangled nanowires with average diameters in the range of 50-180 nm. The nanostructures were single-crystalline rutile structure of SnO2. The PL measurement with the Gaussian fitting exhibited visible light emission bands centered at 576 nm and 638 nm, respectively. We have discussed the possible growth mechanism of the nanostructures.

Abstract: To make a dense CIGS absorber layer, spray deposited CIGS films were annealed in the two-zone RTP furnace in Se atmosphere. More Se supply by increasing Se evaporation temperature or by increasing the flow rate of carrier gas resulted in the larger CIGS grains. However, a thick MoSe2 layer was formed between CIGS and Mo, as the Se supply increased, results in partial detachment of CIGS/MoSe2/Mo layers from the glass substrate. From the result, it was found that the short heat- treatment with high Se vapor pressure is better than the long heat-treatment with low Se vapor pressure. The large CIGS grains without peeling off, can be obtained from the following conditions; Se evaporation temperature of 450oC, substrate temperature of 550oC, annealing time of 5 min, and flow rate of carrier gas of 30 sccm.

Abstract: Cu(In,Ga)3Se5 films were deposited on soda-lime glass substrate by three-stage co-evaporation process. In the film, the band gap increased as the Cu content decreased and also as the Ga content increased. The grain size became smaller as the Ga content increased. In the Cu1.29(In1-xGax)3Se5 system, the maximum hole concentration was 1x1015 /cm3 when the Ga content was 0.5 and its band gap was 1.45 eV. Comparing the conventional CIGS solar cell with Cu0.8(In0.7Ga0.3)Se2 film, the series resistance is too large, indicating that further p-type doping in the Cu(In,Ga)3Se5 film is necessary to improve cell efficiency for the top cell application in CIGS tandem solar cells.

Abstract: Silicone dioxide (SiO2) layer as an electrical insulator and diffusion barrier was deposited on a flexible stainless steel substrate by plasma enhanced CVD process. And we deposited Mo/Na-doped Mo bi-layer back contact on the oxide layer in order to supply Na into the CIGS absorber. Then we deposited CIGS layer by three-stage process using elemental co-evaporation method and completed the solar cell fabrication. Without antireflection coating, the best CIGS solar cell on the stainless steel showed the conversion efficiency of 10.57 % with Jsc = 33.38 mA/cm2 and Voc = 0.519 V and FF = 0.61 for an active area of 0.45 cm2.

Abstract: As an alternative to a CdS buffer layer for Cu(In,Ga)Se2-based solar cells, we prepared In-based buffer layers using a chemical bath deposition method. XPS and XRD analyses revealed that the In-based buffer layers contained In2S3 and InOOH phases. Compared with CdS film, the In-based film, Inx(OOH,S)y, had higher optical transmittance and a shorter absorption edge. The Cu(In,Ga)(Se,S)2 solar cell with the Inx(OOH,S)y buffer layer had better photovoltaic properties than that with a conventional CdS buffer layer. The conversion efficiency of the best Cu(In,Ga)(Se,S)2 solar cell with Inx(OOH,S)y buffer layer was 12.55 % for an active area of 0.19 cm2.