Chonghoon Shin

Triple-Junction Hybrid Tandem Solar Cells with Amorphous Silicon and Polymer-Fullerene Blends

Organic-inorganic hybrid tandem solar cells attract a considerable amount of attention due to their potential for realizing high efficiency photovoltaic devices at a low cost. Here, highly efficient triple-junction (TJ) hybrid tandem solar cells consisting of a double-junction (DJ) amorphous silicon (a-Si) cell and an organic photovoltaic (OPV) rear cell were developed. In order to design the TJ device in a logical manner, a simulation was carried out based on optical absorption and internal quantum efficiency. In the TJ architecture, the high-energy photons were utilized in a more efficient way than in the previously reported a-Si/OPV DJ devices, leading to a significant improvement in the overall efficiency by means of a voltage gain. The interface engineering such as tin-doped In2O3 deposition as an interlayer and its UV-ozone treatment resulted in the further improvement in the performance of the TJ solar cells. As a result, a power conversion efficiency of 7.81% was achieved with an open-circuit voltage of 2.35 V. The wavelength-resolved absorption profile provides deeper insight into the detailed optical response of the TJ hybrid solar cells.

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.

The Effect of Carrier Injection Stress on Boron-Doped Amorphous Silicon Suboxide Layers Investigated by X-ray Photoelectron Spectroscopy

In amorphous silicon solar cells, reducing degradation is one of the key issues in improving cell performance. The degradation of the p-layer can play an important role since it is directly related to the open circuit voltage (Voc) and fill factor (FF) in the cells. In this study, we investigated the changes in boron-doped p-type silicon suboxide (SiOx) layers after carrier injection stress. The boron doping level was varied by controlling B2H6 gas flow rate. When these layers were degraded, the dark conductivity decay decreased from 53% to less than 5%, and the increase in activation energy decreased from 11 to 0.5% depending on the B2H6 gas flow rate increase. Our improvements are explained in conjunction with the three- and four-fold coordinated boron atoms by the shift of the B 1s X-ray photoelectron spectrum. In this paper we present how to improve the stability of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells.

Improving the efficiency of rear emitter silicon solar cell using an optimized n-type silicon oxide front surface field layer

Optical and electrical characteristics of n-type nano-crystalline-silicon oxide (n-µc-SiO:H) materials can be varied to optimize and improve the performance of a solar cell. In silicon heretojunction (SHJ) solar cells, it can be used to improve carrier selectivity and optical transmission at the front side, both of which are vitally important in device operation. For this purpose, the n-µc-SiO:H was investigated as the front surface field (FSF) layer. During film deposition, an increased CO2 flow rate from 0 to 6 sccm resulted in changes of crystalline volume fractions from 57 to 28%, optical band-gaps from 1.98 to 2.21 eV, dark conductivities from 7.29 to 1.1 × 10−5 S/cm, and activation energies from 0.019 to 0.29 eV, respectively. In device applications, a minimum optical reflection was estimated for the FSF layer that was fabricated with 4 sccm CO2 (FSF-4), and therefore obtained the highest external quantum efficiency, although short circuit current density (Jsc) was 38.83 mA/cm2 and power conversion efficiency (PCE) was 21.64%. However, the highest PCE of 22.34% with Jsc = 38.71 mA/cm2 was observed with the FSF prepared with 2 sccm CO2 (FSF-2), as the combined opto-electronic properties of FSF-2 were better than those of the FSF-4.

Development of p-type amorphous silicon oxide — Nano crystalline silicon double layer and its application in n-i-p type amorphous silicon solar cell

Single junction n-i-p type amorphous silicon solar cell was investigated with various p-type window layers. A high doped silicon oxide (P1) layer was used to extract holes from the active layer while a highly conducting micro-crystalline silicon p-type layer was used as an electrical contact layer with the transparent conducting oxide front electrode. When electrical conductivity of the second (P2) layer was raised (to 1.1 S.cm-1) the open circuit voltage and short circuit current density of the cells increased. This P2 layer was placed in between P1 and front electrode. Optical band gap of the p-type layers remain close to 2.0 eV. With an optimum fabrication condition of the p-layers, the open circuit voltage and short circuit current density of the cells were found to reach 900 mV and 11 mA/cm2 respectively.

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.

Analysis of Flow Rate through Channel in New Design of Active Fountain Pen Nanolithography

In this paper, new design AFPN (active fountain pen nanolithography) uses open and close control. Reservoir upper tip is designed. We analyze load of flux and atmospheric pressure from opened part of reservoir. When tip is contacted on surface, flux is outpoured by tips repulsive force. We present analysis that control flux according to force that gives pressure to tip.