Jeong Chul Lee

Highly efficient plasmonic organic optoelectronic devices based on a conducting polymer electrode incorporated with silver nanoparticles

Highly efficient ITO-free polymeric electronic devices were successfully demonstrated by replacement of the ITO electrode with a solution-processed PEDOT:PSS electrode containing Ag nanoparticles (NPs). Polymer solar cells (PSCs) and light emitting diodes (PLEDs) were fabricated based on poly(5,6-bis(octyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole) (PTBT):PC61BM and Super Yellow as a photoactive layer, respectively. The surface plasmon resonance (SPR) effect and improved electrical conductivity by the Ag NPs clearly contributed to increments in light absorption/emission in the active layer as well as the conductivity of the PEDOT:PSS electrode in PSCs and PLEDs. The ITO-free bulk heterojunction PSCs showed a 1% absolute enhancement in the power conversion efficiency (3.27 to 4.31%), and the power efficiency of the PLEDs was improved by 124% (3.75 to 8.4 lm W−1) compared to the reference devices without Ag NPs. The solution-processable conducting polymer, PEDOT:PSS with Ag NPs, can be a promising electrode for large area and flexible optoelectronic devices with a low-cost fabrication process.

Interface modification effect between p-type a-SiC:H and ZnO:Al in p-i-n amorphous silicon solar cells.

Aluminum-doped zinc oxide (ZnO:Al) [AZO] is a good candidate to be used as a transparent conducting oxide [TCO]. For solar cells having a hydrogenated amorphous silicon carbide [a-SiC:H] or hydrogenated amorphous silicon [a-Si:H] window layer, the use of the AZO as TCO results in a deterioration of fill factor [FF], so fluorine-doped tin oxide (Sn02:F) [FTO] is usually preferred as a TCO. In this study, interface engineering is carried out at the AZO and p-type a-SiC:H interface to obtain a better solar cell performance without loss in the FF. The abrupt potential barrier at the interface of AZO and p-type a-SiC:H is made gradual by inserting a buffer layer. A few-nanometer-thick nanocrystalline silicon buffer layer between the AZO and a-SiC:H enhances the FF from 67% to 73% and the efficiency from 7.30% to 8.18%. Further improvements in the solar cell performance are expected through optimization of cell structures and doping levels.

Formation of CuIn1- xAlxSe2 thin films by selenization of metallic precursors in se vapor

CuIn1-xAxlSe2(CIAS) films were obtained by selenization process of metallic precursors. The metallic precursors were deposited sequentially by using sputtering system. As the ratio of Al/(Al+In) in the precursors increased, the chalcopyrite (112) peak shifted to high value and the band-gap of CIAS layer increased to 1.38 eV. However, the bi-layer morphology with well crystallized large grain on the surface and small grain thin bottom layer was observed. Although the sequences of precursors were changed in order to get uniform layer, no distinguishable difference was not observed.

Enhanced Performance of a Polymer Solar Cell upon Addition of Free-Standing, Freshly Etched, Photoluminescent Silicon Nanocrystals

We demonstrate an organic–inorganic hybrid solar cell using poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and silicon nanocrystals (Si-NCs). To achieve an enhanced response in the hybrid layer, Si-NCs were freshly etched and blended with P3HT/PCBM. The incorporation of Si-NCs into the bulk heterojunction structure induced the coupling of optical excitation between the polymers and Si-NCs and led to an extended optical excitation response. A hybrid solar cell exhibited a 26% increase in JSC relative to an identical cell prepared without the Si-NCs. Consequently, improved power conversion efficiency is obtained by the addition of Si-NCs into polymers.

Experimental and simulation study for ultrathin (∼100 μm) mono crystalline silicon solar cell with 156×156 mm2 area

A reduction in silicon material consumption in the photovoltaic industry is required for cost reduction. Using crystalline silicon wafers of less than 120 microns of thickness is a promising way for cost and material reduction in the solar cell production. The standard thickness of crystalline silicon solar cells is currently around 180 microns. If the wafers are thinner than 100 microns in the silicon solar cells, the amount of silicon will be reduced by almost half, which should result in prominent cost reduction. With this aim, many groups have worked with thin crystalline silicon wafers. However, most of them have studied with small size substrates. In this paper, we present the electrical characteristics for thin single crystalline silicon solar cells of 100 and 115 μm thickness and 156×156 mm2 area manufactured through a conventional process. We have achieved 17.2% conversion efficiency with a 115 μm silicon substrate and 16.8% with a 100 μm substrate. This enables the commercialization of the thin crystalline silicon solar cells with high conversion efficiency. We also suggest issues to be solved in thin crystalline silicon solar cell manufacturing.

Light management and efficient carrier generation with a highly transparent window layer for a multijunction amorphous silicon solar cell

Abstract. P-layer of a p-i-n type amorphous silicon solar cell helps in creating a built-in electric field inside the cell; it also contributes to parasitic absorption loss of incident light. Here, we report optimization of these two characteristic contributions of the p-layer of the cell. We used a highly transparent p-type hydrogenated amorphous silicon carbide (p-a-Si1−xCx:H) window layer in an amorphous silicon solar cell. With the increased transparency of the p-type layer, the solar cell showed an improvement in short-circuit current density by 17%, along with improvement in blue response of its external quantum efficiency, although further thinner p-layer showed lower open-circuit voltage. Such a cell shows low light-induced degradation and a promise to be used in high-efficiency multijunction solar cell.

A hybrid solar cell fabricated using amorphous silicon and a fullerene derivative

Hybrid solar cells, based on organic and inorganic semiconductors, are a promising way to enhance the efficiency of solar cells because they make better use of the solar spectrum and are straightforward to fabricate. We report on a new hybrid solar cell comprised of hydrogenated amorphous silicon (a-Si:H), [6,6]-phenyl-C71-butyric acid methyl ester ([71]PCBM), and poly-3,4-ethylenedioxythiophene poly styrenesulfonate (PEDOT:PSS). The properties of these PEDOT:PSS/a-Si:H/[71]PCBM devices were studied as a function of the thickness of the a-Si:H layer. It was observed that the open circuit voltage and the short circuit current density of the device depended on the thickness of the a-Si:H layer. Under simulated one sun AM 1.5 global illumination (100 mW cm(-2)), a power conversion efficiency of 2.84% was achieved in a device comprised of a 274 nm-thick layer of a-Si:H; this is the best performance achieved to date for a hybrid solar cell made of amorphous Si and organic materials.

The influence of filament temperature on crystallographic properties of poly-Si films prepared by the hot-wire CVD method

Abstract This paper presents the deposition and characterization of polycrystalline silicon (poly-Si) films by the hot-wire chemical vapor deposition (HWCVD) method. The filament temperature was determined to be a critical parameter for the deposition of large-grained Si films. Poly-Si films with a moderate lateral grain-size of ∼1 μm and a vertical grain size approximately the same as the film thickness (approx. 3 μm) could be deposited on a glass substrate at a substrate temperature of less than 550°C by increasing the filament temperature to 2000°C. The surface of the films has a natural textured structure, which is believed to give some positive effects on solar cell performance. Some experimental results are presented in order to elucidate these improvements in crystalline properties of the Si films deposited at high filament temperature.

Characterization of Surface Morphology and Light Scattering of Transparent Conducting ZnO:Al Films as Front Electrode for Silicon Thin Film Solar Cells

Changes in the surface morphology and light scattering of textured Al doped ZnO thin films on glass substrates prepared by rf magnetron sputtering were investigated. As-deposited ZnO:Al films show a high transmittance of above 80% in the visible range and a low electrical resistivity of 4.5×10 Ω·cm. The surface morphology of textured ZnO:Al films are closely dependent on the deposition parameters of heater temperature, working pressure, and etching time in the etching process. The optimized surface morphology with a crater shape is obtained at a heater temperature of 350 C, working pressure of 0.5 mtorr, and etching time of 45 seconds. The optical properties of light transmittance, haze, and angular distribution function (ADF) are significantly affected by the resulting surface morphologies of textured films. The film surfaces, having uniformly size-distributed craters, represent good light scattering properties of high haze and ADF values. Compared with commercial Asahi U (SnO :F) substrates, the suitability of textured ZnO:Al films as front electrode material for amorphous silicon thin film solar cells is also estimated with respect to electrical and optical properties.

Structural and electrical properties of polycrystalline silicon films deposited by hot-wire CVD

The polycrystalline silicon (poly-Si) films are deposited on low-temperature glass substrate by hot-wire CVD. The SiH 4 gas flow rate {F(SiH 4 )} is a critical parameter both for deposition rate and for crystalline properties. The poly-Si films deposited at low F(SiH 4 ) with moderate deposition rate (about 3 μm/h) have superior crystalline properties and crystalline volume fraction that exceeds 90%. The films also have natural texture structure on the surface that is strongly recommended in thin-film solar cells in order to obtain high current density by increasing incident light trapping. By increasing F(SiH 4 ) to 10 sccm, the high deposition rate (20 μm/h) is obtained, but crystalline properties deteriorated in these samples. However, these films have high potentials for thick (20-30 μm) solar cell applications due to the high deposition rate and enhanced grain growth; average grain sizes are larger than that of low-F(SiH 4 ) samples although small nano-sized grains still exist, by which crystalline volume fraction was <70%. The secondary ion mass spectroscopy and Fourier transform infrared spectroscopy analysis showed that the films have considerable amount of O and C within the films and this is originated from impurity penetration during storing the samples in atmosphere.