Materials and Interface Optimization of Heterojunction Silicon (HIT) Solar Cells Using in-situ Real-Time Spectroscopic Ellipsometry

2004 ◽  
Vol 808 ◽  
Author(s):  
D.H. Levi ◽  
C.W. Teplin ◽  
E. Iwaniczko ◽  
R.K. Ahrenkiel ◽  
H.M. Branz ◽  
...  
Keyword(s):  
Solar Cells ◽  
Real Time ◽  
Spectroscopic Ellipsometry ◽  
Crystalline Silicon ◽  
Surface Recombination ◽  
Chemical Vapor ◽  
Energy Conversion Efficiency ◽  
Open Circuit ◽  
Analysis Tool

ABSTRACTWe have applied real-time spectroscopic ellipsometry (RTSE) as both an in-situ diagnostic and post-growth analysis tool for hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction with intrinsic thin-layer (HIT) solar cells grown by hot-wire chemical vapor deposition. RTSE enables precise thickness control of the 5 to 25 nm layers used in these devices, as well as monitoring crystallinity and surface roughness in real time. Utilizing RTSE feedback, but without extensive optimization, we have achieved a photovoltaic energy conversion efficiency of 14.1% on an Al-backed p-type Czochralski c-Si wafer coated with thin i and n layers on the front. Open-circuit voltages above 620 mV indicate effective passivation of the c-Si surface by the a-Si:H intrinsic layer. Lifetime measurements using resonant coupled photoconductive decay indicate that surface recombination velocities can approach 1 cm/s. RTSE and transmission electron microscopy show that the intrinsic a-Si:H i-layers grow as a mixture of amorphous and nano-crystalline silicon.

Real-time spectroscopic ellipsometry as an in-situ probe of the growth dynamics of amorphous and epitaxial crystal silicon for photovoltaic applications

2005 ◽  
Vol 862 ◽  
Author(s):  
D.H. Levi ◽  
C.W. Teplin ◽  
E. Iwaniczko ◽  
Y. Yan ◽  
T.H. Wang ◽  
...  
Keyword(s):  
Real Time ◽  
Spectroscopic Ellipsometry ◽  
Crystalline Silicon ◽  
Degree Of Crystallinity ◽  
Analysis Tool ◽  
Crystal Silicon ◽  
Tem Analysis ◽  
Photovoltaic Applications ◽  
Si Wafer

AbstractIn this paper we report on our work using in-situ real time spectroscopic ellipsometry (RTSE) to study the dynamics of hot-wire chemical vapor deposition (HWCVD) of hydrogenated amorphous silicon (a-Si:H) and epitaxial crystal silicon (epi-Si) for photovoltaic applications. We utilize RTSE as both an in-situ diagnostic and a postgrowth analysis tool for a-Si:H/crystalline silicon heterojunction (SHJ) solar cells and epi-silicon films grown by HWCVD. RTSE enables precise thickness control of the 3 to 10 nm thick layers used in the SHJ devices, as well as monitoring crystallinity and surface roughness in real time. With the assistance of in-situ RTSE feedback we have achieved a photovoltaic energy conversion efficiency of 17% on an Al-backed p-type float-zone c-Si wafer. Open-circuit voltages above 650 mV indicate excellent passivation of the c-Si surface by the a-Si:H intrinsic layer. We have used RTSE to obtain information on the degree of crystallinity and the electronic and optical properties of films as a function of deposition conditions. RTSE has indirectly indicated the persistence of a hydrogen layer at the interface between the a-Si:H layer and the crystal silicon substrate. Absorption spectra determined by RTSE have provided guidance in device optimization.We are also applying in-situ RTSE to study the dynamics of HWCVD growth of epi-Si. The goal of this work is to develop low-temperature methods for growing 2-10 μmthick layers of c-Si on c-Si seed layers on glass for solar cell applications. This study presents unique challenges for RTSE, as perfect epitaxial growth of c-Si on a c-Si wafer would produce no change at all in the RTSE spectra. We have found that by monitoring the pseudo-dielectric function in real time during growth we gain immediate feedback on the breakdown of epi-Si growth. Post-deposition analysis of the RTSE data provides quantitative information on the percent of c-Si and a-Si versus film thickness. The RTSE analysis has been confirmed by cross sectional TEM. Based on the rapid feedback provided by RTSE we have surpassed the previous HWCVD maxiumum of 200 nm of epi-Si growth, achieving a maximum thickness of 500 nm of epi-Si. TEM analysis has shown that micron-sized areas of these films achieve 1000 nm of epi-Si thickness.

Advances in the Characterization of Compositionally-graded Layers in Amorphous Semiconductor Solar Cells by Real Time Spectroellipsometry

1996 ◽  
Vol 420 ◽  
Author(s):  
R. W. Collins ◽  
Sangbo Kim ◽  
Joohyun Koh ◽  
J. S. Burnham ◽  
Lihong Jiao ◽  
...  
Keyword(s):  
Solar Cells ◽  
Real Time ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Interface Layer ◽  
Open Circuit ◽  
Amorphous Semiconductor ◽  
Deposition Parameters ◽  
Gas Flow Ratio ◽  
Graded Layers

AbstractWe have developed a real time spectroellipsometry data analysis procedure that allows us to characterize compositionally- graded amorphous semiconductor alloy thin films prepared by plasma-enhanced chemical vapor deposition (PECVD). As an example, we have applied the analysis to obtain the depth-profile of the optical gap and alloy composition with ≤15 Å resolution for a hydrogenated amorphous silicon-carbon alloy (a-Si1−xCx:H) film prepared by continuously varying the gas flow ratio z=[CH4]/{[CH4]+[SiH4]} in the PECVD process. The graded layer has been incorporated at the p/i interface of widegap a-Si1−xCx:H (x∼0.05) p-i-n solar cells, and consistent improvements in open-circuit voltage have been demonstrated. The importance of the graded-layer characterization is the ability to relate improvements in device performance directly to the physical properties of the interface layer, rather to the deposition parameters with which they were prepared.

In-situ Observation of Silicon Epitaxy Breakdown with Real-Time Spectroscopic Ellipsometry

2004 ◽  
Vol 808 ◽  
Author(s):  
Charles W. Teplin ◽  
Dean H. Levi ◽  
Qi Wang ◽  
Eugene Iwaniczko ◽  
Kim M. Jones ◽  
...  
Keyword(s):  
Real Time ◽  
Spectroscopic Ellipsometry ◽  
Chemical Vapor ◽  
In Situ Observation ◽  
Epitaxial Silicon ◽  
Silicon Epitaxy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Hydrogenated Amorphous

ABSTRACTWe use in-situ real-time spectroscopic ellipsometry to observe the breakdown of silicon epitaxy during growth by hot-wire chemical vapor deposition (HWCVD) on Si (100) substrates. Representative data is presented for the two types of epitaxy breakdown that we have observed: 1) an immediate transition to hydrogenated amorphous silicon (a-Si:H), and 2) a slower transition where a-Si:H cones nucleate and grow until they eclipse further epitaxial growth. Simple models, consistent with transmission-electron and atomic-force micrographs, describe the evolution of both types of breakdown showing that real-time spectroscopic ellipsometry is a useful tool for monitoring the growth of epitaxial silicon.

Effects of Progressive SiNx Films on the Performance of Polycrystalline Silicon Solar Cells

2013 ◽  
Vol 724-725 ◽  
pp. 151-155
Author(s):  
Peng Wang ◽  
Xian Fang Gou ◽  
Wei Tao Fan ◽  
Chen Cai Sun
Keyword(s):  
Thin Films ◽  
Solar Cells ◽  
Polycrystalline Silicon ◽  
Surface Passivation ◽  
Crystalline Silicon ◽  
Chemical Vapor ◽  
Open Circuit ◽  
Electrical Performance ◽  
Silicon Solar Cells ◽  
Chemical Vapor Deposition Method

In order to improving the conversion efficiency of polycrystalline silicon solar cells, progressive SiNx thin films were deposited on the surface via Roth&Rau plasma-enhanced chemical vapor deposition method. The effects of progressive SiNx thin films, such as surface passivation, anti-reflection, and electrical performance were systematically investigated. Compared with monolayer films, progressive SiNx thin films have better anti-reflective properties in the wavelength range of 300-500 nm, resulting in improvement of the short wavelength absorption of the crystalline silicon solar cells. Moreover, the bottom of progressive SiNx thin films with high refractive index enhances the surface passivation. Thus, higher open-circuit voltage and fill factor could be obtained by this technique.

scholarly journals Effect of the CO2/SiH4Ratio in the p-μc-SiO:H Emitter Layer on the Performance of Crystalline Silicon Heterojunction Solar Cells

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Jaran Sritharathikhun ◽  
Taweewat Krajangsang ◽  
Apichan Moollakorn ◽  
Sorapong Inthisang ◽  
Amornrat Limmanee ◽  
...  
Keyword(s):  
Solar Cells ◽  
Silicon Oxide ◽  
Crystalline Silicon ◽  
Chemical Vapor ◽  
Dark Conductivity ◽  
Open Circuit ◽  
Very High Frequency ◽  
Emitter Layer ◽  
Heterojunction Solar Cells ◽  
Vapor Deposition Technique

This paper reports the preparation of wide gap p-type hydrogenated microcrystalline silicon oxide (p-μc-SiO:H) films using a 40 MHz very high frequency plasma enhanced chemical vapor deposition technique. The reported work focused on the effects of the CO2/SiH4ratio on the properties of p-μc-SiO:H films and the effectiveness of the films as an emitter layer of crystalline silicon heterojunction (c-Si-HJ) solar cells. A p-μc-SiO:H film with a wide optical band gap (E04), 2.1 eV, can be obtained by increasing the CO2/SiH4ratio; however, the tradeoff betweenE04and dark conductivity must be considered. The CO2/SiH4ratio of the p-μc-SiO:H emitter layer also significantly affects the performance of the solar cells. Compared to the cell using p-μc-Si:H (CO2/SiH4= 0), the cell with the p-μc-SiO:H emitter layer performs more efficiently. We have achieved the highest efficiency of 18.3% with an open-circuit voltage (Voc) of 692 mV from the cell using the p-μc-SiO:H layer. The enhancement in theVocand the efficiency of the solar cells verified the potential of the p-μc-SiO:H films for use as the emitter layer in c-Si-HJ solar cells.

Development of Deposition Phase Diagrams for Thin Film Si:H and Si1-xGex:H Using Real Time Spectroscopic Ellipsometry

2005 ◽  
Vol 862 ◽  
Author(s):  
N. J. Podraza ◽  
G. M. Ferreira ◽  
C. R. Wronski ◽  
R. W. Collins
Keyword(s):  
Phase Diagram ◽  
Phase Diagrams ◽  
Real Time ◽  
Spectroscopic Ellipsometry ◽  
Silicon Germanium ◽  
Crystalline Silicon ◽  
Thick Layer ◽  
Chemical Vapor ◽  
Surface Stability ◽  
Si Substrates

AbstractThe growth of hydrogenated silicon (Si:H) and silicon-germanium alloys (Si1-xGex:H) by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) substrates has been studied by real time spectroscopic ellipsometry (RTSE). The motivation is to develop deposition phase diagrams that can provide greater insight into the optimization of amorphous Si1-xGex:H (a-Si1-xGex:H) for multijunction photovoltaics. In initial studies, the phase diagram for bottom cell a-Si1-xGex:H (Eg ˜ 1.4 eV) is found to exhibit fundamental similarities to that for Si:H when both materials are prepared under standard PECVD conditions that optimize pure a-Si:H. These similarities suggest directions for optimizing a-Si1-xGex:H by identifying conditions under which a smooth, stable surface is obtained to the largest possible bulk layer thickness. In phase diagram development for PECVD Si1-xGex:H on c-Si, it has been found that the highest surface stability and smoothest surfaces are obtained using cathodic deposition (self bias: ˜-20 V) with a H2-dilution level just below that of the amorphous-to-(mixed-phase microcrystalline) [→(a+μc)] transition for a thick layer. Due to the promising nature of these results, full phase diagrams are compared for cathodic and anodic Si1-xGex:H as well as for cathodic and anodic Si:H, all on c-Si substrates. The cathodic phase diagram for Si1-xGex:H reveals a narrow range of significant improvement in surface structural evolution near the →(a+μc) transition, and for a-Si:H reveals an extension of the ultrasmooth protocrystalline regime to a much wider range of thickness.

High-Performance Amorphous Silicon Emitter for Crystalline Silicon Solar Cells

2005 ◽  
Vol 862 ◽  
Author(s):  
T.H. Wang ◽  
E. Iwaniczko ◽  
M.R. Page ◽  
Q. Wang ◽  
D.H. Levi ◽  
...  
Keyword(s):  
Solar Cells ◽  
Amorphous Silicon ◽  
High Performance ◽  
Crystalline Silicon ◽  
Solar Spectrum ◽  
Chemical Vapor ◽  
Type A ◽  
Open Circuit ◽  
Back Surface ◽  
Crystalline Silicon Solar Cells

AbstractThin hydrogenated amorphous silicon (a-Si:H) layers deposited by hot-wire chemical vapor deposition (HWCVD) are studied for use as the emitter in silicon heterojunction (SHJ) solar cells on p-type crystalline silicon wafers. Low interface recombination velocity and high open-circuit voltage are achieved by a low substrate temperature (<150°C) intrinsic a-Si:H deposition which ensures immediate amorphous silicon deposition. This is followed by deposition of n-type a-Si:H at a higher temperature (>200°C) which improves dopant activation and other properties. A prolonged atomic H pretreatment to clean the c-Si surface is actually detrimental because it creates additional defects in the c-Si lattice. However, a brief H pretreatment is beneficial and may render the intrinsic interlayer unnecessary. The n-type a-Si:H thickness must be limited to ~5 nm to minimize current loss, because the phosphorous doped a-Si:H layer has significant absorption in the usable solar spectrum. Using the optimized a-Si:H emitter, we obtain efficiency of nearly 17% on planar float-zone (FZ) silicon and 15% on planar Czochralski (CZ) silicon substrates with aluminum back-surface-field (Al-BSF) and contacts.

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