Chaehwan Jeong

Effective Light Management of Three-Dimensionally Patterned Transparent Conductive Oxide Layers

For effective light harvesting, a design weighting should be implemented in a front geometry, in which the incident light transmits from a surface into a light-active layer. We designed a three-dimensionally patterned transparent conductor layer for effective light management. A transparent conductive oxide (TCO) film was formed as three-dimensional structures. This efficiently drives the incident light at the front surface into a Si absorber to yield a reduction in reflection and an enhancement of current. This indicates that an optimum architecture for a front TCO surface will provide an effective way for light management in solar cells.

Thermally Stable Silver Nanowires-Embedding Metal Oxide for Schottky Junction Solar Cells

Thermally stable silver nanowires (AgNWs)-embedding metal oxide was applied for Schottky junction solar cells without an intentional doping process in Si. A large scale (100 mm(2)) Schottky solar cell showed a power conversion efficiency of 6.1% under standard illumination, and 8.3% under diffused illumination conditions which is the highest efficiency for AgNWs-involved Schottky junction Si solar cells. Indium-tin-oxide (ITO)-capped AgNWs showed excellent thermal stability with no deformation at 500 °C. The top ITO layer grew in a cylindrical shape along the AgNWs, forming a teardrop shape. The design of ITO/AgNWs/ITO layers is optically beneficial because the AgNWs generate plasmonic photons, due to the AgNWs. Electrical investigations were performed by Mott-Schottky and impedance spectroscopy to reveal the formation of a single space charge region at the interface between Si and AgNWs-embedding ITO layer. We propose a route to design the thermally stable AgNWs for photoelectric device applications with investigation of the optical and electrical aspects.

Improvement in electrical properties of sol–gel-derived In-doped ZnO thin film by electron beam treatment

AbstractnIn-doped ZnO thin films were prepared by a sol–gel spin coating method. Since several issues with In doping have been reported, such as degradation of crystallinity and deterioration of electrical resistivity at high In-doping levels, co-doping with Ga and electron beam treatment was demonstrated in this study. When In dopant was added to the ZnO thin film at 0.5xa0mol%, it increased the carrier concentration, thereby reducing the resistivity of the film. In contrast, further doping by Ga in the presence of In did not significantly change the electrical properties. When electron beam treatment was conducted on ZnO films, the optical band gap was increased and the carrier concentration and mobility were increased. In particular, a 0.5xa0mol% In-doped ZnO that received electron beam treatment at 2xa0keV exhibited an electrical resistivity as low as 4.8xa0×xa010−2xa0Ωxa0cm, while 57.1xa0Ωxa0cm was obtained from the pristine ZnO thin film. When the ZnO films were applied to crystalline Si solar cells, conversion efficiency significantly increased from 10.37xa0% for the cell with pristine ZnO thin film to 11.45xa0% with the In-doped and electron beam-treated ZnO thin film.Graphical Abstract

Transparent conductor-embedding nanolens for Si solar cells

We present a large-scale applicable nanolens-embedding solar cell. An electrically conductive and optically transparent indium-tin-oxide (ITO) thin film was coated on a Si substrate. After then, periodically patterned ITO nanodome-arrays were formed on the ITO film by using a nano-imprint method. This structure is effective to reduce the incident light reflection for broad wavelengths and also efficient to drive the incident photons into a light-absorbing Si substrate. There exist two electric fields. One is by a p/n junction and the other is by the light absorption into Si. We designed nanolens structures to overlap two electric fields and demonstrate highly improved solar cell performances of current and voltage values from a planar structure.

Improvement in current density of nano- and micro-structured Si solar cells by cost-effective elastomeric stamp process

Effective incident light should be controlled for improving the current density of solar cells by employing nano- and micro-structures on silicon surface. The elastomeric stamp process, which is more cost effective and simpler than conventional photolithography, was proposed for the fabrication of nano- and micro-structures. Polydimethylsiloxane (PDMS) was poured on a mother pattern with a diameter of 6 μm and a spacing of 2 μm; then, curing was performed to create a PDMS mold. The regular micropattern was stamped on a low-viscosity resin-coated silicon surface, followed by the simple reactive ion etching process. Nano-structures were formed using the Ag-based electroless etching process. As etching time was increased to 6 min, reflectance decreased to 4.53% and current density improved from 22.35 to 34.72 mA/cm2.

Characteristics of the Mg and In co-doped ZnO Thin Films with Various Substrate Temperatures

Mg and In co-doped ZnO (MIZO) thin films with transparent conducting characteristics were successfully prepared on glass substrates by RF magnetron sputtering technique. The Influence of different substrate temperature (from RT to 400°C) on the structural, morphological, electrical, and optical properties of MIZO thin films were investigated. The MIZO thin film prepared at the substrate temperature of 350°C showed the best electrical characteristics in terms of the carrier concentration (4.24×10 20 cm -3 ), charge carrier mobility (5.01 cm 2 V -1 S -1 ), and a minimum resistivity (1.24×10 -4 Ω . cm). The average transmission of MIZO thin films in the visible range was over 80% and the absorption edges of MIZO thin films were very sharp. The bandgap energy of MIZO thin films becomes wider from 3.44 eV to 3.6 eV as the substrate temperature increased from RT to 350°C. However, Band gap energy of MIZO thin film was narrow at substrate temperature of 400°C.