The Effect of Moderate Hydrogen Dilution on Stability and Structure of Amorphous Silicon Deposited by Hot-Wire CVD

2001 ◽  
Vol 664 ◽  
Author(s):  
Urban Weber ◽  
Bernd Schroeder
Keyword(s):  
Hydrogen Bonding ◽  
Solar Cells ◽  
Amorphous Silicon ◽  
Hot Wire ◽  
Solar Cell Performance ◽  
Hydrogen Dilution ◽  
Process Gas ◽  
Before And After ◽  
The Stability ◽  
Substrate Temperatures

ABSTRACTThe effect of moderate hydrogen dilution of the process gas, F(H2)/F(SiH4) = 0 to 3, on the properties of amorphous silicon is discussed for material and solar cells deposited by Hot-Wire CVD. Dielectric properties were obtained from spectroscopic ellipsometry and are related to stability and hydrogen bonding configuration of films deposited with varying hydrogen dilution at different substrate temperatures. The stability was determined by comparing defect densities obtained from photoconductivity spectroscopy in the constant photocurrent mode (CPM) before and after pulsed-light soaking. At low substrate temperatures, which are relevant for the prepara- tion of pin-type solar cells (160-200°C), moderate hydrogen dilution (∼0.3) improves material quality regarding density and network disorder (oscillator bandwidth) as obtained from spectro-scopic ellipsometry, resulting in a higher stability. At higher substrate temperatures (300°C), stability and hydrogen bonding configurations are generally better, but moderate hydrogen dilu-tion already deteriorates these properties compared to material prepared without dilution. The incorporation of Hot-Wire-a-Si:H into pin-type solar cells is also discussed and a good correlation of ellipsometric results with bulk-related properties of solar cell performance is observed. The optimum hydrogen dilution is found to be 0 to 0.3 for i-layer deposition yielding initial efficiencies of up to 8.9% for solar cells entirely fabricated by Hot-Wire CVD.

Amorphous Silicon Alloy Materials and Solar Cells Near the Threshold of Microcrystallinity

1999 ◽  
Vol 557 ◽  
Author(s):  
J. Yang ◽  
S. Guha
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Amorphous Silicon ◽  
Triple Junction ◽  
High Efficiency ◽  
Spectral Response ◽  
High Quality ◽  
Silicon Alloys ◽  
Solar Cell Performance ◽  
Hydrogen Dilution

AbstractOne of the most effective techniques used to obtain high quality amorphous silicon alloys is the use of hydrogen dilution during film growth. The resultant material exhibits a more ordered microstructure and gives rise to high efficiency solar cells. As the hydrogen dilution increases, however, a threshold is reached, beyond which microcrystallites begin to form rapidly. In this paper, we review some of the interesting features associated with the thin film materials obtained from various hydrogen dilutions. They include the observation of linear-like objects in the TEM micrograph, a shift of the principal Si TO band in the Raman spectrum, a sharp, low temperature peak in the H2 evolution spectrum, a shift of the wagging mode in the IR spectrum, and a narrowing of the Si (111) peak in the X-ray diffraction pattern. These spectroscopic tools have allowed us to optimize deposition conditions to near the threshold of microcrystallinity and obtain desired high quality materials. Incorporation of the improved materials into device configuration has significantly enhanced the solar cell performance. Using a spectral-splitting, triple-junction configuration, the spectral response of a typical high efficiency device spans from below 350 nm to beyond 950 nm with a peak quantum efficiency exceeding 90%; the triple stack generates a photocurrent of 27 mA/cm2. This paper describes the effect of the improved materials on various solar cell structures, including a 13% active-area, stable triple-junction device.

Amorphous Silicon-Carbon Alloys for Solar Cells

1993 ◽  
Vol 297 ◽  
Author(s):  
Yuan-Min Li
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Amorphous Silicon ◽  
Light Exposure ◽  
Open Circuit ◽  
Hydrogen Dilution ◽  
Silicon Carbon ◽  
Hydrogenated Amorphous ◽  
Substrate Temperatures ◽  
Open Circuit Voltages

Recent efforts to optimize undoped, glow-discharge hydrogenated amorphous silicon-carbon alloys (a-SiC:H) with 1.9-2.0 eV bandgaps for solar cell applications are reviewed. Hydrogen dilution coupled with relatively low substrate temperatures (below 200 °C) have led to great improvements in the optical and phototransport properties of a-SiC:H films. The issue of alternative carbon feedstocks other than methane (CH4) will be explored. The improved a-SiC:H alloys have resulted in solar cells with high open circuit voltages (V∞ > 1.0 volt) and high fill factors (> 0.7). Further, the a-SiC:H solar cell instability upon prolonged light exposure has been much reduced. Correlation will be made between the properties of bulk undoped a-SiC:H films and the performance of p-i-nsingle junction solar cells using corresponding a-SiC:H thin i-layers.

Stability Studies of Hydrogenated Amorphous Silicon Alloy Solar Cells Prepared with Hydrogen Dilution

1994 ◽  
Vol 336 ◽  
Author(s):  
J. Yang ◽  
X. Xu ◽  
S. Guha
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
Deposition Temperature ◽  
Hydrogenated Amorphous Silicon ◽  
Open Circuit ◽  
Solar Cell Performance ◽  
Silicon Alloy ◽  
Before And After ◽  
Photovoltaic Characteristics ◽  
Hydrogenated Amorphous

ABSTRACTWe have fabricated hydrogenated amorphous silicon alloy solar cells using hydrogen dilutions at 175 °C and 300 °C, and obtained improved photovoltaic characteristics in both the initial and degraded states for the highly diluted cells; both the fill factor and the open-circuit voltage exhibit higher values before and after light soaking. Infrared analyses reveal that for a given deposition temperature the amount of bonded hydrogen has similar concentrations between the high and low hydrogen diluted samples. Optical Modelling shows a 20 MeV difference in their optical bandgap. Defect densities obtained from constant photocurrent measurements give similar values for a given deposition temperature both before and after light soaking, inconsistent with solar cell performance.

DEVELOPMENT OF HIGHLY STABLE HYDROGENATED AMORPHOUS SILICON FILMS FOR APPLICATION IN SOLAR CELLS

2006 ◽  
Vol 20 (14) ◽  
pp. 2035-2047 ◽  
Author(s):  
Q. S. LEI ◽  
Z. M. WU ◽  
J. P. XI ◽  
X. H. GENG ◽  
Y. ZHAO ◽  
...  
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
High Stability ◽  
Hydrogenated Amorphous Silicon ◽  
Light Illumination ◽  
Plasma Power ◽  
Dilution Ratio ◽  
Hydrogen Dilution ◽  
The Stability ◽  
Hydrogenated Amorphous

Highly stable hydrogenated amorphous silicon (a- Si:H ) films were developed by very high frequency plasma enhanced chemical vapor deposition (VHF PECVD). Their electrical and structural properties were studied. The films were applied as i-layers for p-i-n solar cells. The stability of intrinsic films as well as solar cells was studied. Results suggest that a- Si:H films prepared at high hydrogen dilution ratio (R) and low plasma power (PW) have low hydrogen content (CH) and small microstructure factor (RH) and show high stability against light illumination. The device with i-layer prepared at PW=5 W and R=10 shows a high stability with degradation in fill factor and efficiency of 3.23% and 11.64%, respectively, over 1000 hours illumination. However, the device with i-layer prepared at higher plasma power (PW=25 W ) and lower hydrogen dilution ratio (R=5) was much less stable. The stability of the devices is directly related to the stability of the intrinsic materials.

Influence of catalyzer area and design on the growth of intrinsic hot-wire CVD thin-film silicon for photovoltaic applications

2004 ◽  
Vol 808 ◽  
Author(s):  
Markus Kupich ◽  
Dmitry Grunsky ◽  
Bernd Hofferberth ◽  
Bernd Schröder
Keyword(s):  
Solar Cells ◽  
High Efficiency ◽  
Hot Wire ◽  
Deposition Rates ◽  
Hydrogen Dilution ◽  
Process Gas ◽  
High Efficiency Solar Cells ◽  
Absorber Material ◽  
Conversion Efficiencies ◽  
Steel Substrates

ABSTRACTRecently, hot-wire deposited microcrystalline silicon has attracted increasing attention. The use of hot-wire deposited intrinsic μc-Si:H for high efficiency solar cells was demonstrated by Klein et al. [1]. Integration of high-quality intrinsic μc-Si:H into all-hot-wire nip solar cells, prepared close to the transition to amorphous growth using a tantalum catalyzer, resulted in initial and stable efficiencies of 5.4 % on simple stainless steel substrates [2]. However, the deposition rates for the absorber material in both cases remained low, at values around 1 Å/s.In the present study we report on the dependence of deposition rate and material quality on the design and area of the tantalum catalyzer. It was found that different filament geometries require considerable changes in certain deposition conditions to optimize material properties. So, for example, enlarging the catalyzer surface made it necessary to decrease the hydrogen dilution of the process gas, in order to obtain the desired microcrystalline material close to the phase transition. These changes might be understood in terms of alterations of the gas decomposition relations on the catalyzer surface. For these modified conditions, deposition rates in the range of 2.5-10 Å/s could be achieved for μc-Si:H due to the fact that a higher silane fraction of the process gas could be used. For different wire geometries, the optimized intrinsic layers were incorporated into solar cells. Using a catalyzer with modified geometry and enlarged surface area, conversion efficiencies of ν = 4.4 % could be achieved for all-μc-Si:H, all-HWCVD solar cells at a rate of about 3 Å/s.

Annealing Kinetics of Amorphous Silicon Alloy Solar Cells Made at Various Deposition Rates

2001 ◽  
Vol 664 ◽  
Author(s):  
Baojie Yana ◽  
Jeffrey Yanga ◽  
Kenneth Lord ◽  
Subhendu Guha
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Amorphous Silicon ◽  
High Frequency ◽  
Room Temperature ◽  
Defect Density ◽  
Very High Frequency ◽  
Solar Cell Performance ◽  
Kinetics Of ◽  
Very High

ABSTRACTA systematic study has been made of the annealing kinetics of amorphous silicon (a-Si) alloy solar cells. The cells were deposited at various rates using H2 dilution with radio frequency (RF) and modified very high frequency (MVHF) glow discharge. In order to minimize the effect of annealing during light soaking, the solar cells were degraded under 30 suns at room temperature to quickly reach their saturated states. The samples were then annealed at an elevated temperature. The J-V characteristics were recorded as a function of annealing time. The correlation of solar cell performance and defect density in the intrinsic layer was obtained by computer simulation. Finally, the annealing activation energy distribution (Ea) was deduced by fitting the experimental data to a theoretical model. The results show that the RF low rate solar cell with high H2 dilution has the lowest Ea and the narrowest distribution, while the RF cell with no H2 dilution has the highest Ea and the broadest distribution. The MVHF cell made at 8Å/s withhigh H2 dilution shows a lower Ea and a narrower distribution than the RF cell made at 3 Å/s, despite the higher rate. We conclude that different annealing kinetics plays an important role in determining the stabilized performance of a-Si alloy solar cells.

scholarly journals Silicon Heterojunction Solar Cells with p-Type Silicon Carbon Window Layer

Crystals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 402 ◽  
Author(s):  
Chia-Hsun Hsu ◽  
Xiao-Ying Zhang ◽  
Ming Jie Zhao ◽  
Hai-Jun Lin ◽  
Wen-Zhang Zhu ◽  
...  
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
Band Gap ◽  
Flow Rate ◽  
Computer Aided Design ◽  
Hydrogenated Amorphous Silicon ◽  
Wavelength Region ◽  
Window Layer ◽  
Solar Cell Performance ◽  
Hydrogenated Amorphous

Boron-doped hydrogenated amorphous silicon carbide (a-SiC:H) thin films are deposited using high frequency 27.12 MHz plasma enhanced chemical vapor deposition system as a window layer of silicon heterojunction (SHJ) solar cells. The CH4 gas flow rate is varied to deposit various a-SiC:H films, and the optical and electrical properties are investigated. The experimental results show that at the CH4 flow rate of 40 sccm the a-SiC:H has a high band gap of 2.1 eV and reduced absorption coefficients in the whole wavelength region, but the electrical conductivity deteriorates. The technology computer aided design simulation for SHJ devices reveal the band discontinuity at i/p interface when the a-SiC:H films are used. For fabricated SHJ solar cell performance, the highest conversion efficiency of 22.14%, which is 0.33% abs higher than that of conventional hydrogenated amorphous silicon window layer, can be obtained when the intermediate band gap (2 eV) a-SiC:H window layer is used.

Evaluation of Ar-Diluted Silane PECVD for Thin Film Si:H Based Solar Cells

2004 ◽  
Vol 808 ◽  
Author(s):  
J. A. Anna Selvan ◽  
Yuan-Min Li ◽  
Liwei Li ◽  
Alan E. Delahoy
Keyword(s):  
Solar Cells ◽  
Spectral Response ◽  
Nanocrystalline Silicon ◽  
Thin Layers ◽  
Dilution Method ◽  
Critical Question ◽  
Long Wavelength ◽  
Hydrogen Dilution ◽  
Porous Microstructure ◽  
The Stability

ABSTRACTDilution by Ar of silane plasma has been reported to increase the stability of a-Si:H films. A critical question is whether Ar diluted i-layers offer higher stabilized solar cell efficiencies than the conventional hydrogen dilution method. We have fabricated a-Si:H p-i-n solar cells with RF-PECVD i-layers by Ar dilution of silane. Ar dilution ratio (ADR, Ar/SiH4), RF power,pressure, and i-layer thickness were varied. At low ADR < 20, such solar cells show comparable initial efficiencies and stability as those devices having H2-diluted i-layers of similar thickness. For cells made with ADR > 20, the initial efficiency decreases dramatically with further increase in Ar dilution, and light soaking causes only mild changes in efficiencies. The stabilized efficiencies of cells made with high ADR are inferior to the cells produced with low ADR or cells prepared by H2 dilution. Further, Voc of solar cells made with high ADR (> 50) decreases substantially in ambient, indicating a porous microstructure susceptible to oxidation. While thermal annealing improves the Voc, a full recovery of Voc is made by accelerated light soaking.The combination of high power and high ADR can lead to nanocrystalline silicon (nc-Si:H) growth, although nucleation is much more difficult to attain by the Ar dilution method compared to hydrogen dilution. We have succeeded in fabricating p-i-n solar cells with nc-Si:H i-layers prepared by the Ar dilution approach. The double dilution by Ar and hydrogen of silane (Ar+H2+SiH4) can result in nc-Si:H i-layers with enhanced long wavelength spectral response compared to devices incorporating nc-Si:H i-layers grown by H2 dilution only. The nc-Si:H solar cells with Ar+H2 diluted i-layers exhibit no light-induced degradation.Using energetic Ar-rich plasma, in a process much simpler than the traditional nc-Si:H technique, doped a-Si:H thin layers can be prepared to form excellent tunnel junctions for multi-junction solar cells. We demonstrate such a novel, non-contaminating tunnel junction in tandem a-Si/a-Si and a-Si/nc-Si solar cells entirely fabricated in a single-chamber RF-PECVD system.

scholarly journals Hot wire deposited hydrogenated amorphous silicon solar cells

1996 ◽  
Author(s):  
A. H. Mahan ◽  
B. P. Nelson ◽  
E. Iwaniczko ◽  
Q. Wang ◽  
E. C. Molenbroek ◽  
...  
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
Hydrogenated Amorphous Silicon ◽  
Silicon Solar Cells ◽  
Hot Wire ◽  
Hydrogenated Amorphous
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