Deposition of Device Quality μc-Si Films and Solar Cells at High Rates by HWCVD in a W Filament Regime where W/Si Formation is Minimal

2003 ◽  
Vol 762 ◽  
Author(s):  
E. Iwaniczko ◽  
A.H. Mahan ◽  
B. Yan ◽  
L.N. Gedvilas ◽  
D.L. Williamson ◽  
...  
Keyword(s):  
Solar Cells ◽  
Chamber Pressure ◽  
Silicide Formation ◽  
Hot Wire ◽  
Tungsten Filament ◽  
Tandem Solar Cells ◽  
Filament Temperature ◽  
Deposition Parameters ◽  
Si Films ◽  
Filament Surface

Abstractμc-Si has traditionally been deposited by Hot Wire CVD at a low filament temperature. At these temperatures, silicides rapidly form on the filament surface, leading in the case of a tungsten filament to both film reproducibility and filament lifetime issues. By depositing films consecutively using identical deposition parameters, these issues are chronicled for a filament temperature of ∼ 1750°C. Upon increasing the filament temperature to ∼1825-1850°C, these reproducibility and lifetime issues disappear and, by lowering both the substrate temperature and chamber pressure, device quality μc-Si is deposited at high deposition rates in a filament regime where tungsten silicide formation is minimal. Both single junction and tandem solar cells are fabricated using this material, confirming the validity of this approach.

Deposition of Device Quality μc-Si Films and Solar Cells at High Rates by HWCVD in a W Filament Regime where W/Si Formation is Minimal

2003 ◽  
Vol 762 ◽  
Author(s):  
E. Iwaniczko ◽  
A.H. Mahan ◽  
B. Yan ◽  
L.N. Gedvilas ◽  
D.L. Williamson ◽  
...  
Keyword(s):  
Solar Cells ◽  
Chamber Pressure ◽  
Silicide Formation ◽  
Hot Wire ◽  
Tungsten Filament ◽  
Tandem Solar Cells ◽  
Filament Temperature ◽  
Deposition Parameters ◽  
Si Films ◽  
Filament Surface

Abstractμc-Si has traditionally been deposited by Hot Wire CVD at a low filament temperature. At these temperatures, silicides rapidly form on the filament surface, leading in the case of a tungsten filament to both film reproducibility and filament lifetime issues. By depositing films consecutively using identical deposition parameters, these issues are chronicled for a filament temperature of ∼ 1750°C. Upon increasing the filament temperature to ∼ 1825-1850°C, these reproducibility and lifetime issues disappear and, by lowering both the substrate temperature and chamber pressure, device quality μc-Si is deposited at high deposition rates in a filament regime where tungsten silicide formation is minimal. Both single junction and tandem solar cells are fabricated using this material, confirming the validity of this approach.

Microcrystalline Silicon for Solar Cells at High Deposition Rates by Hot Wire Cvd

2002 ◽  
Vol 715 ◽  
Author(s):  
R. E. I. Schropp ◽  
Y. Xu ◽  
E. Iwaniczko ◽  
G. A. Zaharias ◽  
A. H. Mahan
Keyword(s):  
Solar Cells ◽  
Substrate Temperature ◽  
Volume Fraction ◽  
Silicon Layer ◽  
Hot Wire ◽  
Crystalline Volume Fraction ◽  
Microcrystalline Silicon ◽  
Deposition Rates ◽  
Deposition Parameters ◽  
Si Films

AbstractWe have explored which deposition parameters in Hot Wire CVD have the largest impact on the quality of microcrystalline silicon (μc-Si) made at deposition rates (Rd) < 10 Å/s for use in thin film solar cells. Among all parameters, the filament temperature (Tfil) appears to be crucial for making device quality films. Using two filaments and a filament-substrate spacing of 3.2 cm, μc-Si films, using seed layers, can be deposited at high Tfil (∼2000°C) with a crystalline volume fraction < 70-80 % at Rd's < 30 Å/s. Although the photoresponse of these layers is high (< 100), they appear not to be suitable for incorporation into solar cells, due to their porous nature. n-i-p cells fabricated on stainless steel with these i-layers suffer from large resistive effects or barriers, most likely due to the oxidation of interconnected pores in the silicon layer. The porosity is evident from FTIR measurements showing a large oxygen concentration at ∼1050 cm-1, and is correlated with the 2100 cm-1 signature of most of the Si-H stretching bonds. Using a Tfil of 1750°C, however, the films are more compact, as seen from the absence of the 2100 cm-1 SiH mode and the disappearance of the FTIR Si-O signal, while the high crystalline volume fraction (< 70-80 %) is maintained. Using this Tfil and a substrate temperature of 400°C, we obtain an efficiency of 4.9 % for cells with a Ag/ZnO back reflector, with an i-layer thickness of only ∼0.7 μm. High values for the quantum efficiency extend to very long wavelengths, with values of 33 % at 800 nm and 15 % at 900 nm, which are unequalled by a-SiGe:H alloys. Further, by varying the substrate temperature to enable deposition near the microcrystalline to amorphous transition (‘edge’) and incorporating variations in H2 dilution during deposition of the bulk, efficiencies of 6.0 % have been obtained. The Rd's of these i-layers are 8-10 Å/s, and are the highest to date obtained with HWCVD for microcrystalline layers used in cells with efficiencies of ∼6 %.

The influence of filament temperature on crystallographic properties of poly-Si films prepared by the hot-wire CVD method

2001 ◽  
Vol 395 (1-2) ◽  
pp. 188-193 ◽  
Author(s):  
Jeong Chul Lee ◽  
Ki Hwan Kang ◽  
Seok Ki Kim ◽  
Kyung Hoon Yoon ◽  
Jinsoo Song ◽  
...  
Keyword(s):  
Hot Wire ◽  
Filament Temperature ◽  
Cvd Method ◽  
Si Films

Thin Film a-Si/poly-Si Multibandgap Tandem Solar Cells With Both Absorber Layers Deposited by Hot Wire Cvd

2001 ◽  
Vol 664 ◽  
Author(s):  
R.E.I. Schropp ◽  
C.H.M. Van Der Werf ◽  
M.K. Van Veen ◽  
P.A.T.T. Van Veenendaal ◽  
R. Jimenez Zambrano ◽  
...  
Keyword(s):  
Solar Cells ◽  
Substrate Temperature ◽  
Band Gap ◽  
Steel Substrate ◽  
Light Trapping ◽  
Chemical Vapor ◽  
Hot Wire ◽  
Tandem Solar Cells ◽  
Hydrogen Dilution ◽  
P Type

ABSTRACTThe first competitive a-Si/poly-Si multibandgap tandem cells have been made in which the two intrinsic absorber layers are deposited by Hot Wire Chemical Vapor Deposition (HWCVD). These cells consist of two stacked n-i-p type solar cells on a plain stainless steel substrate using plasma deposited n- and p-type doped layers and Hot-Wire deposited intrinsic (i) layers, where the i-layer is either amorphous (band gap 1.8 eV) or polycrystalline (band gap 1.1 eV). In this tandem configuration, all doped layers are microcrystalline and the two intrinsic layers are made by decomposing mixtures of silane and hydrogen at hot filaments in the vicinity of the substrate. For the two layers we used individually optimized parameters, such as gas pressure, hydrogen dilution ratio, substrate temperature, filament temperature, and filament material. The solar cells do not comprise an enhanced back reflector, but feature a natural mechanism for light trapping, due to the texture of the (220) oriented poly-Si absorber layer and the fact that all subsequent layers are deposited conformally. The deposition rate for the throughput limiting step, the poly-Si i-layer, is ≍ 5-6 Å/s. This layer also determines the highest substrate temperature required during the preparation of these tandem cells (500 °C). The initial efficiency obtained for these tandem cells is 8.1 %. The total thickness of the silicon nip/nip structure is only 1.1 µm.

High-Growth Rate a-Si:H Deposited by Hot-Wire CVD

1994 ◽  
Vol 336 ◽  
Author(s):  
P. Brogueira ◽  
V. Chu ◽  
J.P. Conde
Keyword(s):  
Flow Rate ◽  
Chemical Vapor ◽  
High Growth ◽  
Dark Conductivity ◽  
High Growth Rate ◽  
Hot Wire ◽  
Tungsten Filament ◽  
Hydrogen Flow ◽  
Deposition Parameters ◽  
Pressure Regime

ABSTRACTWe present a study of the optoelectronic and structural properties of a-Si:H deposited by Hot-Wire chemical vapor deposition (HW-CVD) from SiH4 and H2 at “Medium” (Tfil ≃ 1500°C) and “high” (Tfil ≃ 1900 °C) filament temperatures. For each tungsten filament temperature regime, the following deposition parameters are varied: (i) pressure (p ∼ 10−2 — 0.5 Torr); (ii) substrate temperature (Tsub ∼ 180 — 270 °C); (iii) silane flow rate (FsiH4 ∼ 1 — 10 ccm) and (iv) hydrogen flow rate (FH2 ∼ 0 — 10 seem). Films deposited at Tfil ∼ 1900 °C in a low pressure regime (p ∼ 2.7 × 10−2Torr) using flows of 5 sccm for both H2 and SiH4 had high deposition rates (rd ∼ 8 Ås−1). These films showed an optical bandgap, E9Tauc ≃ 1.7 eV, a dark conductivity σd ∼ 10−8Scm−1 with an activation energy Eα,σd ≃ 0.8 eV, and photoconductivity σph ≥ 10−5Scm−1 (σph ∼ 10−5). Films deposited at Tju = 1500 °C and p ≃ 0.3 Torr, showed 1.7 < E9Tauc < 2 eV, 10−5 < σd < 10−3Scm−1, 0.2 < Eα,σ d < 0.5 eV and σph/Σd < 102. For the same Tfit and p ∼ 3 × 10−2 — 0.1 Torr, the films show 1.7 < E9Tauc < 2 eV, 10−3 < Σd < 10−1Scm−1 and σph/σd < 1. Films deposited using molybdenum and rhenium filaments at Tfil ≃ 1900 °C show E9Tauc ≃ 1.7 eV and σd ∼ σph ∼ 10−7Scm−1

Low Defect Density Microcrystalline-Si Deposited by the Hot Wire Technique

1998 ◽  
Vol 507 ◽  
Author(s):  
A. H. Mahan ◽  
M. Vanecek ◽  
A. Poruba ◽  
V. Vorlicek ◽  
R. S. Crandall ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Defect Density ◽  
Structural Data ◽  
Hot Wire ◽  
Very High Frequency ◽  
Deposition Parameters ◽  
Optical And Electronic Properties ◽  
High Filament ◽  
Si Films ◽  
Substrate Temperatures

ABSTRACTThe optical and electronic properties of a series of microcrystalline silicon (μ-Si) films, deposited by the hot wire (HW) technique, are reported. Preliminary results suggest, using moderate H2 /SiH4 dilution ratios and substrate temperatures (320°C), high filament temperatures, and no H gas purifier, that the subgap absorption for these films, measured using the constant photocurrent (CPM) method, can be as low as that obtained for films deposited by the very high frequency glow discharge (VHF-GD) technique. The film dark conductivities of the HW samples, ranging as low as 2.0 × 10−8 (ohm cm)−1, lend further credance to these low defect values. At the same time, the optical absorption in the region > 1.6 eV is higher than that previously observed for the VHF-GD deposited samples. The present results, discussed in the context of the film microcrystalline fraction, suggest that there is no unique, good quality, low defect density μ-Si material, and that different deposition techniques can be used to successfully deposit device quality gc-Si. We also present optical and structural data for films deposited at lower substrate temperatures and higher deposition rates, and suggest combinations of deposition parameters to be used that may further improve the electronic properties of these films.

Preparation of microcrystalline silicon nip solar cells and amorphous–microcrystalline nipnip tandem solar cells entirely by hot-wire CVD

2006 ◽  
Vol 501 (1-2) ◽  
pp. 268-271 ◽  
Author(s):  
Markus Kupich ◽  
Dmitry Grunsky ◽  
Prabhat Kumar ◽  
Bernd Schröder
Keyword(s):  
Solar Cells ◽  
Hot Wire ◽  
Microcrystalline Silicon ◽  
Tandem Solar Cells

Higher efficiency of n-i-p solar cells by Hot-Wire CVD at moderate temperatures

2001 ◽  
Vol 664 ◽  
Author(s):  
Marieke K. van Veen ◽  
Ruud E.I. Schropp
Keyword(s):  
Solar Cells ◽  
Fill Factor ◽  
Open Circuit Voltage ◽  
Stainless Steel Substrate ◽  
Steel Substrate ◽  
Open Circuit ◽  
Hot Wire ◽  
Tandem Solar Cells ◽  
Back Reflectors ◽  
Absorbing Layer

ABSTRACTHot-Wire deposited amorphous silicon is an excellent material for the incorporation as the absorbing layer in n-i-p solar cells. We decreased the deposition temperature from 430 °C to 250 °C, keeping device quality (opto-)electrical properties of the a-Si:H layers. This enables application of Hot-Wire deposited a-Si:H in p-i-n structures and tandem solar cells. Layers deposited at 250 °C have been applied in efficient n-i-p and n-i-p/n-i-p solar cells. The deposition rate of the intrinsic layer was about 10 Å/s. No optical enhancements, like texturing or back reflectors, were used. Single-junction cells with a fill factor of 0.72 and an open-circuit voltage of 0.89 V have been produced. On a flexible stainless steel substrate, an initial efficiency of 7.2 % was recorded. Tandem cells also show a high fill factor (0.71) and open-circuit voltage (1.70 V), resulting in an initial efficiency of 8.5 %.

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