• Korean Journal of Materials Research
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• v.27 no.2
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• pp.107-112
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• 2017

The BCBJ (Back Contact and Back Junction) or back-lit solar cell design eliminates shading loss by placing the pn junction and metal electrode contacts all on one side that faces away from the sun. However, as the electron-hole generation sites now are located very far from the pn junction, loss by minority-carrier recombination can be a significant issue. Utilizing Medici, a 2-dimensional semiconductor device simulation tool, the interdependency between the substrate thickness and the minority-carrier recombination lifetime was studied in terms of how these factors affect the solar cell power output. Qualitatively speaking, the results indicate that a very high quality substrate with a long recombination lifetime is needed to maintain the maximum power generation. The quantitative value of the recombination lifetime of minority-carriers, i.e., electrons in p-type substrates, required in the BCBJ cell is about one order of magnitude longer than that in the front-lit cell, i.e., $5{\times}10^{-4}sec$ vs. $5{\times}10^{-5}sec$. Regardless of substrate thickness up to $150{\mu}m$, the power output in the BCBJ cell stays at nearly the maximum value of about $1.8{\times}10^{-2}W{\cdot}cm^{-2}$, or $18mW{\cdot}cm^{-2}$, as long as the recombination lifetime is $5{\times}10^{-4}s$ or longer. The output power, however, declines steeply to as low as $10mW{\cdot}cm^{-2}$ when the recombination lifetime becomes significantly shorter than $5{\times}10^{-4}sec$. Substrate thinning is found to be not as effective as in the front-lit case in stemming the decline in the output power. In view of these results, for BCBJ applications, the substrate needs to be only mono-crystalline Si of very high quality. This bars the use of poly-crystalline Si, which is gaining wider acceptance in standard front-lit solar cells.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.8
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• pp.463-467
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• 2000

In this paper, the new LIGBT structures with trap injection are proposed to improve switching characteristics of the conventional SOI LIGBT. The Simulations are performed in order to investigate the effects of the positiion, whidth and concentration of trap injection region with a reduced minority carrier lifetime using 2D device simulator MEDICI. Their electrical characteristics are analyzed and the optimum design parameters are extracted. As a result of simulation, the turn off time for the model A with the trap injection is $0.78\mus$. These results indicate the improvement of about 2 times compared with the conventional SOI LIGBT because trap injection prevents minority carriers which is stored in the n-drift region during turn off switching. The latching current is $1.5\times10^{-4}A/\mum$ and forward blocking voltage is 168V which are superior to those of conventional structure. It is shown that the trap injection is very effective to reduce the turn off time with a little increasing of on-state voltage drop if its design and process parameters are optimized.

• Journal of the Korean Ceramic Society
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• v.51 no.3
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• pp.197-200
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• 2014

We investigated the influence of blistering on $Al_2O_3$/SiON stacks and $Al_2O_3$/SiNx:H stacks passivation layers. $Al_2O_3$ film provides outstanding Si surface passivation quality. $Al_2O_3$ film as the rear passivation layer of a p-type Si solar cell is usually stacked with a capping layer, such as $SiO_2$, SiNx, and SiON films. These capping layers protect the thin $Al_2O_3$ layer from an Al electrode during the annealing process. We compared $Al_2O_3$/SiON stacks and $Al_2O_3$/SiNx:H stacks through surface morphology and minority carrier lifetime after annealing processes at $450^{\circ}C$ and $850^{\circ}C$. As a result, the $Al_2O_3$/SiON stacks were observed to produce less blister phenomenon than $Al_2O_3$/SiNx:H stacks. This can be explained by the differences in the H species content. In the process of depositing SiNx film, the rich H species in $NH_3$ source are diffused to the $Al_2O_3$ film. On the other hand, less hydrogen diffusion occurs in SiON film as it contains less H species than SiNx film. This blister phenomenon leads to an increase insurface defect density. Consequently, the $Al_2O_3$/SiON stacks had a higher minority carrier lifetime than the $Al_2O_3$/SiNx:H stacks.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.2
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• pp.120-124
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• 2000

In this paper, the effects of trap distribution on switching characteristis of a lateral insulated gate bipolar transistor (LIGBT) are investigated. The simulations are performed in order to to analyze the effect of the positon, width and concentration of trap distribution model with a reduced minority carrier lifetime using 2D device simulator MEDICI. The turn off time for the proposed LIGBT model A with the trap injection is 0.8$mutextrm{s}$. These results indicate the improvement of about 2 times compared with the conventional LIGBT. It is shown that the trap distribution model is very effective to reduce the turn-off time with a little increasing of on-state voltage drop.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.46.1-46.1
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• 2010

Surface passivation of crystalline silicon(c-Si) surface with a-Si:H thin films has been investigated by using quasi-steady-state photo conductance(QSSPC) measurements. Analyzing the influence of a-Si:H film thickness, process gas ratio, deposition temperature and post annealing temperature on the passivation properties of c-Si, we optimized the passivation conditions at the substrate temperature of $200-250^{\circ}C$. Best surface passivation has been obtained by post-deposition annealing of a-Si:H film layer. Post annealing around the deposition temperature was sufficient to improve the surface passivation for silicon substrates. We obtained effective carrier lifetimes above 5.5 ms on average.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.406-406
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• 2016

To get high efficiency n-type crystalline silicon solar cells, passivation is one of the key factor. Tunnel oxide (SiO2) reduce surface recombination as a passivation layer and it does not constrict the majority carrier flow. In this work, the passivation quality enhanced by different chemical solution such as HNO3, H2SO4:H2O2 and DI-water to make thin tunnel oxide layer on n-type crystalline silicon wafer and changes of characteristics by subsequent annealing process and firing process after phosphorus doped amorphous silicon (a-Si:H) deposition. The tunneling of carrier through oxide layer is checked through I-V measurement when the voltage is from -1 V to 1 V and interface state density also be calculated about $1{\times}1012cm-2eV-1$ using MIS (Metal-Insulator-Semiconductor) structure . Tunnel oxide produced by 68 wt% HNO3 for 5 min on $100^{\circ}C$, H2SO4:H2O2 for 5 min on $100^{\circ}C$ and DI-water for 60 min on $95^{\circ}C$. The oxide layer is measured thickness about 1.4~2.2 nm by spectral ellipsometry (SE) and properties as passivation layer by QSSPC (Quasi-Steady-state Photo Conductance). Tunnel oxide layer is capped with phosphorus doped amorphous silicon on both sides and additional annealing process improve lifetime from $3.25{\mu}s$ to $397{\mu}s$ and implied Voc from 544 mV to 690 mV after P-doped a-Si deposition, respectively. It will be expected that amorphous silicon is changed to poly silicon phase. Furthermore, lifetime and implied Voc were recovered by forming gas annealing (FGA) after firing process from $192{\mu}s$ to $786{\mu}s$. It is shown that the tunnel oxide layer is thermally stable.

• Korean Journal of Materials Research
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• v.4 no.8
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• pp.921-926
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• 1994

The characteristics of gate oxide significantly depend on the last chemical solution used in cleaning process. The standard RCA, HF-last, SC1-last, and HF-only processes are the pre-gate oxide cleaning processes utilized in this experiment. Cleaning process was followed by thermal oxidation in oxidation furnace at $900^{\circ}C$. A 100$\AA$ gate oxide was grown and characterized with using lifetime detector, VPD AAS, SIMS, TEM, and AFM. The results of HF-last and HF-only were shown to be very effective to remove the metallic impurities. And these two splits also showed long minority carrier lifetimes. The surface and interface morphologies of the oxide were examined with AFM and TEM. The rough surface morphologies were observed with the cleaning splits containing the SC1 solution. The smooth surface and interface was observed with the HF-only cleaning process.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.149-149
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• 2010

The double-layer antireflection (DLAR) coatings have significant advantages over single-layer antireflection (SLAR) coatings. This is because they will be able to cover a broad range of the solar spectrum which would enhance the overall performance of solar cells. Moreover films deposited at high frequency are expected to show excellent and UV-stable passivation in the refractive index that we adopted. In this work, we present a novel DLAR coating using SiNx:H thin films with refractive indices 1.9 and 2.3 as the top and bottom layers. This approach is cost effective when compared to earlier DLAR coatings with two different materials. SiNx:H films were deposited by Plasma enhanced chemical vapor deposition (PECVD) technique using $SiH_4$, $NH_3$ and $N_2$ gases with flow rates 20~80sccm, 200sccm and 85 sccm respectively. The RF power, plasma frequency and substrate temperature for the deposition were 300W, 13.56 MHz and $450^{\circ}C$, respectively. The optimum thickness and refractive indices values for DLAR coatings were estimated theoretically using Macleod simulation software as 82.24 nm for 1.9 and 68.58 nm for 2.3 respectively. Solar cells were fabricated with SLAR and DLAR coatings of SiNx:H films and compared the cell efficacy. SiNx:H> films deposited at a substrate temperature of $450^{\circ}C$ and that at 300 W power showed best effective minority carrier lifetime around $50.8\;{\mu}s$. Average reflectance values of SLAR coatings with refractive indices 1.9, 2.05 and 2.3 were 10.1%, 9.66% and 9.33% respectively. In contrast, optimized DLAR coating showed a reflectance value as low as 8.98% in the wavelength range 300nm - 1100nm.

• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.267-274
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• 2001

Removal of Cr, Ni and Cu impurities on Si surfaces using remote plasma-excited hydrogen was investigated. Si surfaces were contaminated intentionally by acetone with low purity. To determine the optimum process condition, remote plasma-excited hydrogen cleaning was conducted for various rf-powers and plasma exposure times. After remote plasma-excited hydrogen cleaning, Si surfaces were analyzed by Total X-ray Reflection Fluorescence(TXRF), Surface Photovoltage(SPV) and Atomic Forece Microscope(AFM). The concentrations of Cr, Ni and Cu impurities were reduced and the minority carrier lifetime increased after remote plasma-excited hydrogen. Also RMS roughness decreased by more than 30% after remote plasma-excited hydrogen cleaning. AFM analysis results also show that remote plasma-excited hydrogen cleaning causes no damage to the Si surface. TXRF analysis results show that remote plasma-excited hydrogen cleaning is effective in eliminating metallic impurities from Si surface only if it is performed under an optimum process conditions. The removal mechanism of the Cr, Ni and Cu impurities using remote plasma-excited hydrogen treatments is proposed to be the lift-off during removal of underlying chemical oxides.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.461-465
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• 2016

n-type silicon shows the better tolerance towards metal impurities with a higher minority carrier lifetime compared to p-type silicon substrate. Due to better lifetime stability as compared to p-type during illumination made the photovoltaic community to switch toward n-type wafers for high efficiency silicon solar cells. We fabricated the front electrode of the n-type solar cell with AgAl paste. The electrodes characteristics of the AgAl paste depend on the contact junction depth that is closely related to the firing temperature. Metal contact depth with p+ emitter, with optimized depth is important as it influence the resistance. In this study, we optimize the firing condition for the effective formation of the metal depth by varying the firing condition. The firing was carried out at temperatures below $670^{\circ}C$ with low contact depth and high contact resistance. It was noted that the contact resistance was reduced with the increase of firing temperature. The contact resistance of $5.99m{\Omega}cm^2$ was shown for the optimum firing temperature of $865^{\circ}C$. Over $900^{\circ}C$, contact junction is bonded to the Si through the emitter, resulting the contact resistance to shunt. we obtained photovoltaic parameter such as fill factor of 76.68%, short-circuit current of $40.2mA/cm^2$, open-circuit voltage of 620 mV and convert efficiency of 19.11%.