Seung Yeop Myong

Highly stable and textured hydrogenated ZnO thin films

We investigated intentionally hydrogenated zinc oxide (ZnO:H) fabricated by combining photoassisted metalorganic chemical vapor deposition and mercury-sensitized hydrogen addition methods. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved surface roughness of the ZnO:H film due to an enhancement of (1120) orientation. The high-quality ZnO:H film is promising as a back reflector material for thin-film solar cells.

Extremely Transparent and Conductive ZnO:Al Thin Films Prepared by Photo-Assisted Metalorganic Chemical Vapor Deposition (photo-MOCVD) Using AlCl3(6H2O) as New Doping Material.

Extremely transparent and conductive ZnO:Al thin films were successfully prepared by a photo-assisted metalorganic chemical vapor deposition (photo-MOCVD) technique at a temperature of 140° C using diethylzinc and H2O as source materials. The vapor from an aqueous solution of aluminum chloride hydrate ( AlCl3(6H2O)) was used as a doping gas. ZnO:Al thin films with a minimum resistivity of 6.22×10-4 Ω cm were obtained. Their total transmittance at 550 nm was 91%. Moreover, the average transmittance in the wavelength region of 400 nm to 1200 nm was over 91%. The new Al-doping method using AlCl3(6H2O) by the photo-MOCVD, proposed for the first time in this study, is economical as well as safe, and high-quality ZnO:Al can be successfully applied to a transparent conductive electrode for large area thin-film solar cells.

Improvement of pin-type amorphous silicon solar cell performance by employing double silicon-carbide p -layer structure

We investigated a double silicon-carbide p-layer structure consisting of a undiluted p-type amorphous silicon-carbide (p-a-SiC:H) window layer and a hydrogen diluted p-a-SiC:H buffer layer to improve a pin-type amorphous silicon based solar cell. Solar cells using a lightly boron-doped (1000 ppm) buffer layer with a high conductivity, low absorption, well-ordered film structure, and slow deposition rate improves the open-circuit voltage (Voc), short-circuit current density, and fill factor by reducing recombination in the buffer layer and at p/buffer and buffer/i interfaces. It is found that a natural hydrogen treatment generated throughout the buffer layer deposition onto the p-a-SiC:H window layer is an advantage of this double p-layer structure. We achieved a considerable initial conversion efficiency of 11.2% without any back reflector.

High efficiency protocrystalline silicon/microcrystalline silicon tandem cell with zinc oxide intermediate layer

The authors develop a hydrogenated protocrystalline silicon (pc-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) double-junction solar cell structure employing a boron-doped zinc oxide (ZnO:B) intermediate layer. Highly stable intrinsic pc-Si:H and μc-Si:H absorbers are prepared by a 60MHz very-high-frequency plasma-enhanced chemical vapor deposition technique. Degenerate ZnO:B intermediate and back reflectors are deposited via a metal organic chemical vapor deposition technique. Because the ZnO:B intermediate layer reduces the potential thickness for the pc-Si:H absorber in the top cell, this double-juncion structure is a promising candidate to fabricate highly stable Si-based thin-film solar cells. Consequently, the high conversion efficiency of 12.0% is achieved.

Double amorphous silicon-carbide p-layer structures producing highly stabilized pin-type protocrystalline silicon multilayer solar cells

We have applied double p-type amorphous silicon-carbide (p-a-SiC:H) layer structures to pin-type protocrystalline silicon (pc-Si:H) multilayer solar cells. The less-pronounced initial short-wavelength quantum efficiency variation against the biased voltage and the wide overlap of dark current—voltage (JD-V) and short-circuit current—open-circuit voltage (Jsc-Voc) characteristics prove that the double p-a-SiC:H layer structure successfully reduces recombination at the p∕i interface. Therefore, we achieved highly stabilized efficiency of 9.0% without any backreflector.

Inclusion of nanosized silicon grains in hydrogenated protocrystalline silicon multilayers and its relation to stability

Photoluminescence and Fourier transform infrared spectroscopy measured at room temperature produce strong evidence that nanosized silicon (nc-Si) grains embedded in hydrogenated protocrystalline silicon (i-pc-Si:H) multilayers. Thus, we propose the structure of the i-pc-Si:H multilayer possessing isolated nc-Si grains and their wrapping layers with a high hydrogen concentration embedded in highly hydrogen-diluted sublayers. The isolated nc-Si grains may act as radiative recombination centers of photoexcited carriers, and hence suppress the photocreation of dangling bonds caused by the nonradiative recombination in amorphous silicon matrix. Because of the repeatedly layered structure, the i-pc-Si:H multilayers have a fast light-induced metastability with a low degradation.

In situ ultraviolet treatment in an Ar ambient upon p-type hydrogenated amorphous silicon–carbide windows of hydrogenated amorphous silicon based solar cells

We proposed an in situ postdeposition ultraviolet treatment in an Ar ambient (UTA) to improve the p∕i interface of amorphous silicon based solar cell. We have increased the conversion efficiency by ∼16% by improving the built-in potential and reducing recombination at the p∕i interface. Through spectroscopic ellipsometry and Fourier-transform infrared measurements, it is concluded that the UTA process induces structural modification of the p-type hydrogenated amorphous silicon–carbide (p-a-SiC:H) window layer. An ultrathin p-a-SiC:H contamination layer formed during the UTA process acts as a buffer layer at the interface.

Highly conductive boron-doped nanocrystalline silicon-carbide film prepared by low-hydrogen-dilution photo-CVD method using ethylene as a carbon source

Boron-doped nanocrystalline silicon-carbide (p-nc-SiC:H) films with a low-concentration of hydrogen-dilution were grown by a mercury-sensitized photo-chemical vapor deposition method using silane (SiH4), hydrogen (H2), diborane (B2H6), and ethylene (C2H4) as a carbon source. From the Raman and FTIR spectrum measurements, the p-nc-SiC:H film is composed of nanosize crystal silicon embedded in a hydrogenated amorphous silicon-carbide matrix. A dark conductivity as high as 1:7 � 10 � 1 S/cm, with an optical bandgap is 2.0 eV, and a crystal volume fraction of 50%, were obtained. We tested these films as window material for amorphous silicon solar cells, obtaining an initial conversion efficiency of 10.4% without using any back reflectors. 2002 Elsevier Science B.V. All rights reserved.

Natural hydrogen treatment effect during formation of double amorphous silicon-carbide p layer structures producing high-efficiency pin-type amorphous silicon solar cells

We proposed a double p-type amorphous silicon-carbide (p‐a‐SiC:H) layer structure to improve the p∕i interface of pin-type amorphous silicon based solar cells. We found a natural hydrogen treatment involving an etch of the defective undiluted p‐a‐SiC:H window layer before the hydrogen-diluted p‐a‐SiC:H buffer layer deposition and an improvement of the order in the window layer. It is beneficial to increase overall solar cell parameters by successfully reducing recombination at the p∕i interface.

Effect of hydrogen dilution on carrier transport in hydrogenated boron-doped nanocrystalline silicon-silicon carbide alloys

The effect of the hydrogen dilution ratio on characteristics of hydrogenated boron-doped nanocrystalline silicon-silicon carbide alloy (p-nc-Si–SiC:H) films is investigated. Hydrogen coverage near the growing surface causes nanocrystallization by retarding the reactions of the precursors. It was found that p-nc-Si–SiC:H alloys have two different kinds of carrier transport mechanisms: one is the thermally activated hopping conduction between neighboring crystallites near room temperature and the other is the band tail hopping conduction below 150K. However, the film at the onset of the nanocrystalline growth exhibits a different behavior due to a large band tail disorder.