Junhee Jung

Impedance Spectroscopic Study of p-i-n Type a-Si Solar Cell by Doping Variation of p-Type Layer

We investigated p-i-n type amorphous silicon (a-Si) solar cell where the diborane flow rate of the p-type layer was varied and the solar cell was measured static/dynamic characteristics. The p/i interface of the thin film amorphous silicon solar cells was studied in terms of the coordination number of boron atoms in the p layer. p-type layer and p/i interface properties were obtained from the X-ray photoelectron spectroscopy (XPS) and impedance spectroscopy. One of the solar cells shows open circuit voltage (𝑉oc)=880 mV, short circuit current density (𝐽sc)=14.21 mA/cm2, fill factor (FF)=72.03%, and efficiency (𝜂)=8.8% while the p-type layer was doped with 0.1%. The impedance spectroscopic measurement showed that the diode ideality factor and built-in potential changed with change in diborane flow rate.

Fabrication of honeycomb textured glass substrate and nanotexturing of zinc oxide front electrode for its application in high efficiency thin film amorphous silicon solar cell

Abstract. A significant part of broad band sunlight remains unabsorbed in a simple structured amorphous silicon solar cell. This absorption can be enhanced by adopting a light-trapping scheme with the help of a textured front surface and back reflector. For this purpose, honeycomb-type texture was fabricated on a glass surface by chemical etching. A 3  μm×3  μm honeycomb patterned optical-mask was used to create an image-pattern of an etch-mask on the glass surfaces. We used 0.5% hydrofluoric acid (HF) as an etchant solution with an optimized etching time ranging between 25 and 28 min. This single textured glass shows an enhancement in diffused transmission of light. In solar cell application, a 630-nm-thick Al-doped ZnO (AZO) layer was deposited over the textured glass surface. An additional random etching was carried out on the AZO with 1% HF acid solution for 10 s. This results to a double textured AZO superstrate on which solar cells were fabricated. The solar cells show higher short circuit current density to 17.2  mA/cm2. Finally, we obtained photovoltaic conversion efficiency of an optimized solar cell as 10.75% (with the corresponding Jsc as 17.03  mA/cm2).

Reduction in Photocurrent Loss and Improvement in Performance of Single Junction Solar Cell Due to Multistep Grading of Hydrogenated Amorphous Silicon Germanium Active Layer

Single junction solar cells were fabricated with intrinsic hydrogenated amorphous silicon germanium (a-SiGe:H) as the active layer, that shows a 10% photovoltaic conversion efficiency. The a-SiGe:H active layer of the solar cells of type-A had constant band gap materials while that of type-B had a four step graded band gap by composition gradient (CG). The cells with composition gradient show an enhancement in fill factor and open circuit voltage (V oc) by 5% and 20 mV respectively, with respect to a cell without the graded band gap active layer. Such an enhanced device performance is attributed to reduction in recombination loss of photo-generated electron hole pairs. The effect of this photo-current loss was investigated in the electrical bias dependent external quantum efficiencies (EQE), illumination dependent current-voltage measurements and dark current-voltage characteristics. The device parameters like reverse saturation current density (J o), series resistance (R s) and diode quality factor (n) were also estimated. In comparison to the cell without the composition gradient, the EQE shows a reduced recombination loss across the whole wavelength range for the cell with the CG. Furthermore, the introduction of the CG results in a significantly increased shunt resistance from 720 to 1200 Ω.cm 2. The estimated n values of the cells under dark operating condition, decreases from 1.8 to 1.7 along with J o from 3 × 10 −7 down to 4.5 × 10 −8 A/cm 2 with CG, while the same parameters decreased from 3.73 to 3.06, 2.96 × 10 −6 to 3.05 × 10 −7 A/cm 2 respectively under AM1.5G insolation.

HF etched glass substrates for improved thin-film solar cells

A hemisphere-array textured glass substrate was fabricated for the development of an improved thin-film (TF) silicon solar cell. The HF-H2SO4-etchant system influenced the light path owing to the formation of the strong fluorine-containing HSO3F acid. In particular, the etching system of the various HF concentration with a constant H2SO4 solution is related to make an improvement of optical transmittance and light trapping structure without a uniform pattern. According to the specular transmittance measurements, the haze ratio was maintained for the glass sample etched with 35% HF in the longer-wavelength region. The proposed substrate was implemented in a TF-Si solar cell, and an improved conversion efficiency was observed according to the short-circuit current density owing to the increase in the haze ratio. This morphology, therefore, induces more scattering at the front side of the cell and leads to an improvement of the open circuit voltage gain for the HF 25% cell. It will be helpful to understand the application of thin film solar cell based on the HF-H2SO4 etching system for the readers.

Advanced triple junction solar cell by employing inorganic-organic hybrid materials

We employed a novel inorganic-organic hybrid triple junction solar cell (IOHTC), with an inorganic silicon tandem cell (ITC) that is series connected to an organic solar cell (OSC) at the back of the ITC. The ITC is used to absorb the short wavelength part of the solar spectrum, while the organic bottom cell utilizes the long wavelength part of the spectrum. The IOHTC was fabricated with hydrogenated amorphous silicon (a-Si:H) and PTB7:PCBM as active layers. The optical gap (Eg) of the active layers of the front to the back cells was 1.83 eV, 1.80 eV and 1.55 eV, respectively. The efficiency of the optimized IOHTC reached a maximum of 7.70% with high open circuit voltage (Voc) 2.33 V. The observed Voc of the IOHTC was 96.31% of the sum of the Voc of the individual component cells. In one of the IOHTC, the total current density (Jsc) increased by 11.19% and 14.13% as compared with total Jsc of the OSC and ITC, respectively.

Carrier Injection Related Stability of Intrinsic Hydrogenated Amorphous Silicon Film and Solar Cells

In this paper, we report the stability of hydrogenated amorphous silicon (a-Si:H) thin films and solar cells for various carrier injections. The intrinsic films were prepared with different hydrogen dilutions. We observed that the a-Si:H film had a 25.4% decline in photocurrent due to the carrier injection. The photoluminescence peak within 1.1 to 1.7 eV increased towards the lower photon energy, due to the bias stress. The Urbach energy for the film degraded from 59 to 85 meV under a similar condition. We also observed a 24% drop in efficiency of the solar cell, due to a forward bias stress for 10 h.

P02.57: Compensatory hyperplasia of the contralateral kidney: usefulness in the differential diagnosis of invisible single kidney in the fetus

by obstetric ultrasound. A 19-year-old primigravid woman was referred at 38 weeks of gestation for an obstetric ultrasound examination because of upper abdominal calcifications. Sonographic scan revealed a live fetus appropriate to the gestational age and no apparent structural abnormalities except for multiple non-shadowing echogenic mass within the upper abdomen. The echogenic mass was located only at fetal gallbladder region. Fetal gallstones were suspected and the couple was informed about the situation. The woman gave birth to a healthy, 3500 g, female newborn at 40 weeks. Postnatal ultrasound showed a dilatated gallbladder and multiple echogenic gallstones. Physical examination as well as laboratory studies were all within normal range. Conservative treatment with ursodeoxycholic acid has been initiated and follow-up scheduled. The baby is now two months of age and is doing well. We conclude that fetal gallstones should be considered in the differential diagnosis of localized calcifications within the fetal liver. Conservative management with ursodeoxycholic acid should be the choice of treatment.