410 IEEE TRANSACTIONS ON ELECTRON DEVICES. VOL. 37. NO. 2. FEBRUARY 1990 CuInSe2 Cells and Modules KIM W. MITCHELL, MEMBER, IEEE,CHRIS EBERSPACHER, JAMES H. ERMER, KAREN L. PAULS, AND DAVE N. PIER, MEMBER, IEEE Abstract-Recent CulnSez (CIS) photovoltaic technology advances include the demonstration of 14.1-percent active area efficient test cells and the fabrication of monolithic integrated modules with power out- puts of 112 W/mZ on 940 cm2 and 91.4 W/m2 on 3900 cm'. Packaged modules are stable outdoors. Studies indicate a recombination con- trolled junction mechanism and imply a wide CIS compositional range over which high-efficiencyjunctions are possible. Processing improve- ments already demonstrated on test cells and 940 cm2 modules will yield 52-W, 3900-cm2 CIS modules. I. INTRODUCTION uInSe2 (CIS) is a promising material for high-power, C low-cost photovoltaics (PV), both as a stand-alone single junction and as the narrow-bandgap component of a tandem junction [1]-[3]. Fig. 1 compares the photon currents generated in CIS, CdTe, thin-film sili- con : hydrogen alloys (TFS), and crystalline silicon cal- culated from the optical absorption coefficients and as- suming no reflection losses [4]-[7]. The photon current increases as a function of optical path length (i.e., ab- sorber layer thickness), and .Ima, is the maximum avail- able photon current density for the material. For CIS, 90 percent of the photons are absorbed in a thickness of less than 1 pm, so that a CIS film thickness of only 1-3 pm is sufficient for thin-film PV applications. 11. CIS CELL RESULTS The highest active-area CIS cell efficiency to date is 14.1 percent for a 3.5-cm2 ZnO/thin CdS/CIS/ Mo/glass cell [8]. Based on a 3.8-cm2 total cell area, the efficiency translates to 13.0 percent. The basic structure of this cell is shown in Fig. 2. Light enters through a 1- 3-pm-thick ZnO layer that acts as a transparent front con- ducting electrode and as a partial antireflection (AR) coat- ing [9], [lo]. The surface texture of the ZnO layer s!~- presses optical reflection losses. A thin (less than 500 A ) CdS layer between the ZnO and the CIS forms the elec- tronic junction with minimal optical absorption [ 101-[12]. The 2-3-pm-thick CIS layer is the photoactive absorber layer. A MO back contact completes the electrical con- nection to the cell. The supporting substrate is typically soda-lime glass. As shown in Fig. 3, the 14.1-percent ac- tive area efficient CIS cell has a 41.0-mA/cm2 J,,, 508- mV V,,,, and 0.677 fill factor (FF) measured under 100- Manuscript received July 21, 1989; revised September 15, 1989. This work was supported in part by the Solar Energy Research Institute under Contract ZB-7-06003-3. The authors are with ARC0 Solar, Inc., Camarillo, CA 93010. IEEE Log Number 8932666. 0 0.5 1 1.5 2 Optical Path Length (pm) ASTM air mass 1.5, 100 mWlcm2 global spectrum Fig. 1. Photon current versus optical path length. Top Metallization Grid 7 1.5 prn' ZnO .1_ I Thin High - Resistivity 1 CdS i MO Fig. 2. CIS solar cell cross section. Area: 3.5 cm2 Jsc: 41.0 mAlcm2 Eft 14.1% 5 1 VOC: 508 mV 5 ,o FF 0.677 0 0.1 0.2 0.3 0.4 0.5 Voltage 0 (100 mWlcm2 SERl AM 1.5 Global Spectrum, 25%) Fig. 3. 14.1-percent ZnO/thin CdS/CIS solar cell I-V curve. mW /cm2 ASTM air mass (AM) 1.5 global spectrum [ 131. Reducing front ZnO resistance using improved grid de- sign would increase the fill factor to 0.715 and the effi- ciency to 14.9 percent. Although small amounts of Ga (see Section IV) were present in this device, as shown below, the spectral response indicates the quantum effi- ciency is identical to a device not containing Ga. 0018-9383/90/0200-0410$01 .OO 0 1990 IEEE I T
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410 IEEE TRANSACTIONS ON ELECTRON DEVICES. VOL. 37. NO. 2. FEBRUARY 1990
CuInSe2 Cells and Modules KIM W. MITCHELL, MEMBER, IEEE, CHRIS EBERSPACHER, JAMES H. ERMER, KAREN L. PAULS,
AND DAVE N. PIER, MEMBER, IEEE
Abstract-Recent CulnSez (CIS) photovoltaic technology advances include the demonstration of 14.1-percent active area efficient test cells and the fabrication of monolithic integrated modules with power out- puts of 112 W/mZ on 940 cm2 and 91.4 W/m2 on 3900 cm'. Packaged modules are stable outdoors. Studies indicate a recombination con- trolled junction mechanism and imply a wide CIS compositional range over which high-efficiency junctions are possible. Processing improve- ments already demonstrated on test cells and 940 cm2 modules will yield 52-W, 3900-cm2 CIS modules.
I. INTRODUCTION uInSe2 (CIS) is a promising material for high-power, C low-cost photovoltaics (PV), both as a stand-alone
single junction and as the narrow-bandgap component of a tandem junction [1]-[3]. Fig. 1 compares the photon currents generated in CIS, CdTe, thin-film sili- con : hydrogen alloys (TFS), and crystalline silicon cal- culated from the optical absorption coefficients and as- suming no reflection losses [4]-[7]. The photon current increases as a function of optical path length (i.e., ab- sorber layer thickness), and .Ima, is the maximum avail- able photon current density for the material. For CIS, 90 percent of the photons are absorbed in a thickness of less than 1 pm, so that a CIS film thickness of only 1-3 pm is sufficient for thin-film PV applications.
11. CIS CELL RESULTS The highest active-area CIS cell efficiency to date is
14.1 percent for a 3.5-cm2 ZnO/thin CdS/CIS/ Mo/glass cell [8]. Based on a 3.8-cm2 total cell area, the efficiency translates to 13.0 percent. The basic structure of this cell is shown in Fig. 2. Light enters through a 1- 3-pm-thick ZnO layer that acts as a transparent front con- ducting electrode and as a partial antireflection (AR) coat- ing [9], [lo]. The surface texture of the ZnO layer s!~- presses optical reflection losses. A thin (less than 500 A ) CdS layer between the ZnO and the CIS forms the elec- tronic junction with minimal optical absorption [ 101-[12]. The 2-3-pm-thick CIS layer is the photoactive absorber layer. A MO back contact completes the electrical con- nection to the cell. The supporting substrate is typically soda-lime glass. As shown in Fig. 3, the 14.1-percent ac- tive area efficient CIS cell has a 41.0-mA/cm2 J,,, 508- mV V,,,, and 0.677 fill factor (FF) measured under 100-
Manuscript received July 21, 1989; revised September 15, 1989. This work was supported in part by the Solar Energy Research Institute under Contract ZB-7-06003-3.
The authors are with ARC0 Solar, Inc., Camarillo, CA 93010. IEEE Log Number 8932666.
0 0.5 1 1.5 2 Optical Path Length (pm)
ASTM air mass 1.5, 100 mWlcm2 global spectrum
Fig. 1. Photon current versus optical path length.
Top Metallization Grid
7 1.5 prn ' ZnO .1_ I Thin High
- Resistivity 1 CdS
i M O
Fig. 2. CIS solar cell cross section.
Area: 3.5 cm2 Jsc: 41.0 mAlcm2
Eft 14.1% 5 1 VOC: 508 mV 5 ,o F F 0.677
0 0.1 0.2 0.3 0.4 0.5 Voltage 0
(100 mWlcm2 SERl AM 1.5 Global Spectrum, 25%)
Fig. 3. 14.1-percent ZnO/thin CdS/CIS solar cell I-V curve.
mW /cm2 ASTM air mass (AM) 1.5 global spectrum [ 131. Reducing front ZnO resistance using improved grid de- sign would increase the fill factor to 0.715 and the effi- ciency to 14.9 percent. Although small amounts of Ga (see Section IV) were present in this device, as shown below, the spectral response indicates the quantum effi- ciency is identical to a device not containing Ga.
0018-9383/90/0200-0410$01 .OO 0 1990 IEEE
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MITCHELL et al . : CuInSe, CELLS AND MODULES
0.9 ~
0.8 -
~ 0.7 ~
0
f o.6 - E 0.5 ~
E 2 0.4 ~
3 0.3 -
1
41 I
o.2 0.1 I \
, -- 0.3 0.5 0.7 0.9 1.1 1.3
0 A-. Wavelength (pm)
Fig. 4 . Quantum efficiency of 14.1-percent efficient CIS cell.
Fig. 6. Dark I-V behavior for 12.4-percent CIS cell
TABLE I TEMPERATURE-DEPENDENT LIGHT I-c.‘ DATA FOR 12.4-PERCENT CIS CELL
299 276 255 232 210 188 166 144 122 100
40.8 40.9 41.1 41.1 41.4 41.1 40.7 40.6 41.0 38.7
455 499 540 581 621 659 69 1 7 18 738 742
64.9 67.2 68.9 69.9 69.9 68.8 66.1 60.3 47.9 25.3
12.0 13.7 15.3 16.7 18.0 18.6 18.6 17.6 14.5 7.3
t~~~ and efficiency data based on 3.17 c.2 active area.
For the 14.1-percent CIS cell, the spectral response (Fig. 4) is described by
QE = (1 - R ) * exp [ - Q ! Z ~ O * tznoI
* exp [ - Q!CdS * lCdS1
* [ 1 - exp ( - %IS * W c d
[1 + %IS * LCIS)I] (1)
where R is the front reflection loss, Q! is the optical ab- sorption coefficient [4], t is the thickness of the respective layers, W is the depletion width, and L is the minority- carrier diffusion length. Typical values of Wand L are 0.4 and 0.5 pm, respectively. ZnO plasma absorption, evi- dent at wavelengths longer than 900 nm, reduces J,, by about 1 mA/cm2, depending on the ZnO electron con- centration and carrier mobility [ 121.
111. CIS JUNCTION ANALYSIS
Development of high-efficiency CIS cells and modules requires an understanding of the mechanisms that control junction behavior. This section summarizes the results from an analysis of ZnO/thin CdS/CIS cells presented elsewhere [ 141. The room-temperature dark I- V curve for a 12.2-percent efficient cell with a 40.6-mA/cm2 J,,, 455- mV V,,, and 0.661 fill factor, shown in Fig. 5 , implies a reverse saturation current Jo of 7.2 x lo-’ A/cm2 and a 1.67 diode factor, using a linear regression curve fitting routine. The superposition of the J,,-V,, data on the dark I-V curve indicate similar junction behavior in the light and in the dark. The J,, is proportional to light intensity, as measured from 0.64 to 100 mW/cm2. For the specific geometry of the 12.2-percent cell, series resistance, pri- marily from the front ZnO, accounts for much of the dif- ference between the measured fill factor and the calcu- lated ideal fill factor of 0.708 [14].
The dark I-V temperature dependence for a similar 12.4-percent CIS cell is shown in Fig. 6, spanning a tem- perature range from 100 to 300 K. The CIS current den-
T
412 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 37, NO. 2. FEBRUARY 1990
13 - 12 - 1 1 - 10 - 9 -
3 8 -
- i x
7 -
6 -
5 -
4 -
S -
l4 -1 1 Q +
0
Q 0 + O O * + + O Q
8 + 0 + o +
0 0 +
sity J is described as a function of the junction voltage 5 (where 5 = Vu - JR,, Vu is the applied voltage, and R, is the series resistance) by a recombination controlled cur- rent above 200 K given by
J = Jo[exp ( q y / n k T ) - 11 (2)
in parallel with a 5-kCl-cm2 shunt resistance with a less than 1 -Cl-cm2 series resistance. The calculated 0.494-eV Jo activation energy E, agrees with the interpretation for recombination of E, equal to one-half of the junction built- in voltage (0.99 eV) [ 5 ] . Below 200 K, two parallel tun- neling mechanisms with a rapidly increasing series resis- tance at lower temperatures define the junction behavior
Decreasing temperature typically increases V,,, fill fac- tor, and efficiency due to a lower Jo unless compensated by high series resistance. At 166 K, the efficiency of the 12.4-percent CIS cell increases to 19.4 percent with a 675- mV V,,, 39.7-mA/cm2 J,,, and 0.723 fill factor. Table I summarizes the temperature dependence of the PV param- eters for the 12.4-percent cell. The J,, is constant at 40.8 mA/cm2 from 299 to 122 K when corrected for fluctua- tions in light intensity. The lower J,, at 100 K is related to a suppressed Z-V caused by the onset of high series resistance. V,, data above 165 K extrapolate to a 0 K value of 0.99 V with a slope of - 1.78 mV/K. At temperatures below 165 K, a reduced slope in V,, versus temperature is a consequence of the change in the CIS junction mech- anism.
The complexity of thin-film CIS devices requires fur- ther analysis in order to provide an exact physical inter- pretation of the junction mechanisms. Compositional and
~ 4 1 .
doping variations in the CIS, trapping states at the inter- face and in the bulk, localized growth defects, nonuni- formities in the junction, grain surfaces, stress-induced defects, the nature of the thin CdS interfacial layer, the ZnO transparent conductive layer, and the Mo/CIS back contact all must be considered.
Efficiency gains for CIS and other chalcopyrite alloys will be derived primarily from improved V,, and fill factor due to increased understanding and control of material and device quality.
IV. COMPOSITIONAL EFFECTS ON CIS CELL PERFORMANCE
The variation of CIS cell performance with composition has been investigated by varying the metals ratio in the CIS absorber film. For example, gallium has been added in low concentrations to explore the influence of small concentrations of dopants and alloys. Substituting gallium for 15 at% or less of the indium content of a stoichio- metric CuInSe2 film does not significantly alter the junc- tion photocurrent density, indicating that the optical bandgap is not significantly increased. Cell efficiency var- ies slowly with composition, exhibiting a broad plateau between Cu/(In + Ga) ratios of 0.9-1.0 (Fig. 7). The variation of cell efficiency with composition is driven pri- marily by variations in V,, and the fill factor (Fig. 8). V,, plateaus over a ratio of 0.88-1 .O. The fill factor decreases slowly for ratios above 0.95. J,, is relatively independent of composition. Overall, these results imply a wide com- positional range over which high-efficiency junctions are possible.
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MITCHELL er al.: CuInSe, CELLS AND MODULES
O M - 0.44 - 0 . u - 0.42 -
413
0 + * 0 + + + O 0
+ e +
8
0.32 - 0.3 -
O a -
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0
0
I I I I I
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0
0 +
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0.5 -
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E 25 -
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5 -
so 1 0 0
o l I I I-
1 1 " I '
I
1.1 1.2 0.8 0.9
h/(h+Qo) 0 M A + M E e Lotc
Fig. 8. CIS cell (a) Vo,, (b) fill factor, and (c) J,, as functions of metals ratio.
V. CIS MODULE DEVELOPMENT cm2 ( 128.1 x 30.5 cm), 53-cell CIS module is illustrated in Fig. 9. The module interconnect region is shown in the expanded cross section. The cell spacing is 0.557 cm. The MO isolation scribe, 18 pm wide, is cut with a 1.06-pm- wavelength Nd: YAG laser. The ZnO/Mo interconnect
The development of CIS modules has advanced signif- icantly [2], [SI, [ l l ] , [12], [15]-[18]. A detailed discus- sion is presented elsewhere [18]. The layout for a 3916-
I
414 IEEE TRANSACTIONS ON ELECTRON DEVICES. VOL. 37, NO. 2. FEBRUARY 1990
32.2 cm ~ 30.6crn
e G L A S S
Fig. 9. Layout for CIS 53-cell 3900-cm2 module.
No Series Resistance-
Sheet Resistance
4 ohms/sq - - - 5 ohms/sq
10 ohrns/sq
, I I , I
380 400 420 440 460 480 500
I /
380 400 420 440 460 480 500
VOc per cell (mV)
Fig. 10. Modeled CIS (a) module power and (b) fill factor.
is made through a 61-pm-wide via created in the CIS. This via is made using either laser or mechanical scribing techniques. The nominal contact resistance is in the range
of 0.2-0.5 mQ-cm2. The ZnO/ZnO isolation scribe is also performed by either mechanical or laser scribing.
The modeled power output and fill factor dependencies
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MITCHELL et al.: CuInSe, CELLS AND MODULES
Voc: 25.5 V
200 Power: 10.5W c3 0.639
Aperture Eft: 11.2% Active Area Eft: 11.7%
415
of a 50-cell 845-cm2 aperture area CIS module on cell V,, and ZnO sheet resistance are shown in Fig. 10. The pro- jected increases in module power with improvements in cell V,,, J,,, and ZnO sheet resistance are:
1) 0.27 W per 10-mV increase in cell V,,; 2) 0.15 to 0.20 W per mA/cm2 increase in cell J,,; 3) 0.09 W per Q / 0 decrease in ZnO sheet resistance. Translating these results to the larger 3900-cm2 module
1) 1.25 W per 10-mV increase in cell Vac; 2) 0.70 to 0.93 W per mA/cm2 increase in cell J,,; 3) 0.42 W per Q / O decrease in ZnO sheet resistance. ZnO sheet resistances are 4-5 Q / O for 3-pm-thick
films. The analysis assumes identical performance from all cells, a 40-mA/cm2 J,,, a 0 .3 -Q/0 MO sheet resis- tance, a 1-mQ-cm2 interconnect contact resistance, and a 1.8 junction diode factor, based on measured data. Cell V,, improvements are especially leveraging to module performance gains.
For CIS modules, performance is dependent on the uni- formities of CIS junction quality and ZnO front electrode sheet resistance. The ZnO thickness and sheet resistance, targeted at 2-3 pm and 5-7 Q/!I respectively, vary typ- ically less than +15 percent across a 4140-cm2 module. The uniformity of CIS junction performance is mapped by measuring the variation of photovoltage V,, across the module. The individual cell V,,'s vary only +4 percent across a finished 3900-cm2 module. Excellent longitudi- nal junction uniformity is also demonstrated in Fig. 11, which maps individual cell V,,'S for five module segments cut from this module.
A 55-cell, 30 X 30 cm CIS module has achieved 10.5 W, which equates to 11.2-percent aperture and 11.7-per- cent active area efficiencies, respectively, based on 938- cm2 aperture and 897-cm2 active areas. As shown in Fig. 12, the module has a 641-mA I,, (39.3-mA/cm2 J,,), a 25.5-V Vo, (464 mV per cell), and a 0.639 fill factor. Interconnects 254 pm wide result in a 95-percent active module area [8].
The highest CIS module power to date is 35.8 W, mea- sured on a 3916-cm2, 53-cell monolithic module. The re- spective aperture and active area efficiencies are 9.1 and 9.8 percent. As shown in Fig. 13, the module has a 2.54-A I,, (37.0-mA/cm2 J, , ) , a 23.5 V,, (443 mV per cell), and a 0.598 fill factor. Table I1 compares the per- formance of the best 3900- and 900-cm2 modules fabri- cated to date. For the larger module, lower cell V,, and fill factor result from a lower junction quality, lower ZnO uniformity, and pattern-induced shunting on the larger areas. At present the interconnect widths on 3900-cm2 modules are wider than on the 900-cm2 modules, resulting in approximately 3-percent lower active area and Z,,. Re- solving these issues will yield 43.6 W on 3900-cm2 mod- ule areas. As indicated in Table 11, implementing the pro- cess used to fabricate the 14.1-percent CIS cell will produce 51.9-W, 3900-cm2 modules with 13.3-percent aperture efficiencies.
illustrated in Fig. 9 gives
'y
Fig. 11. 3900-cmZ CIS module segmented VOc per cell map.
Thin-film CIS modules are at present packaged for en- vironmental durability using techniques developed for packaging TFS products [15]. Electrical ribbons are sol- dered to the module bus pads. A cover glass sheet is lam- inated to the module plate using thermally cured ethylene vinyl acetate (EVA) to form a “glass/glass” laminate. Optical reflection from the cover glass reduces I,, by 3-4 percent, but V,, and the fill factor remain essentially un- changed through the lamination process (Table 111).
VI. CIS MODULE STABILITY Initial outdoor exposure testing of CIS laminated mod-
ules shows promising stability, as illustrated in Fig. 14. Two CIS modules, placed separately under open-circuit and resistive loads at the Solar Energy Research Institute outdoor PV test site, showed little change over the six- month initial period of testing [38]. Although CIS thin- film module packaging requires further development, sta- ble CIS junctions are implied.
ACKNOWLEDGMENT The progress reported in this paper is the product of the
contributions and teamwork of the CIS group of ARCO Solar.
REFERENCES [ I ] K. W. Mitchell, in Proc. Ist Int. PV Science Eng. Conf. (Kobe, Ja-
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[5] K. W. Mitchell, Evaluation of the CdSKdTe Heterojunction Solar
[6] K. L. Eskenas and K. W. Mitchell, in Proc. 18th IEEE PV Spec.
[7] W. R. Runyan, Silicon Semiconductor Technology. New York:
[8] K. Mitchell, C . Eberspacher, J . Ermer, and D. Pier, in Proc. 20th
[9] R. R. Potter, C. E. Eberspacher, and L. B. Fabick, in Proc. 19th
[lo] U. V. Choudary, Y. Shing, R. Potter, J. Ermer, and V. Kapur, United
[ 1 I ] K. Mitchell et a l . , in Proc. 3rd Int. Photovoltaic Science Eng. Conf.
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[I41 K. W. Mitchell and H. I. Liu, in Proc. 20th IEEE PV Spec. Conf.,
[I51 C. Eberspacher, B. Felder, R. R. Potter, and R. D. Wieting, in Proc.
[16] R. Mickelsen, B . J . Stanbeny, J . E. Avery, and W . S . Chen, in Proc.
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*
Kim W. Mitchell (S’74-M’76) received the B.S. degree with honors in applied physics from the California Institute of Technology, Pasadena, and the M.S. and Ph.D. degrees in materials science from Stanford University, Stanford, CA.
At Sandia Laboratories, he served as Technical Manager for Sandia’s high-concentration PV R&D programs and developed analyses of the perfor- mance of photodiodes for analog and digital com- munication in ionizing radiation environments. Then at the Solar Enerev Research Institute. he ”,
managed the emerging materials and high-efficiency concentrator subtasks and pursued in-house research on thin-film materials including CuInSez and CdTe. In 1982, he joined ARCO Solar, where he is currently Principal Scientist and Senior Science Advisor in R&D. As manager of Research and Analysis, he directs a group addressing high-efficiency CuInSe, single- and tandem-junction cell and module development, new promising PV mate- rials and devices, and advanced measuring techniques. He received the first SERI Patent Award and has published extensively.
Dr. Mitchell is a member of the American Physical Society and the American Vacuum Society.
*
Chris Eberspacher received the B.S. degree in physics from the University of Texas and the Ph.D. degree in applied physics from Stanford University, Stanford, CA.
He joined ARCO Solar in 1983 as a Senior Re- search Scientist in the thin-film CdTe research group and is currently Director, CIS Research and Development. He is an author of several technical publications in the field of solid-state devices and photovoltaics.
MITCHELL et al.: CuInSe, CELLS AND MODULES 417
James H. Ermer received the B.S. degree in chemical engineering from California State Uni- versity, Northridge.
He is a Senior Research Engineer at ARCO So- lar where he manages research on thin-film CuInSe2 (CIS) materials and patterning processes necessary for monolithic modules. He has been active in CIS research since joining ARCO Solar in 1980. During this time, he has been extensively involved both in the design and development of advanced processing equipment and in the re-
search and development of thin-film CIS materials processing. His patents span a wide range of thin-film CIS deposition techniques and device struc- tures. He has written several technical publications in the field of thin-film deposition and photovoltaics.
Mr. Ermer is a member of the American Vacuum Society, the American Society of Vacuum Coaters, and the American Institute of Chemical En- gineers.
* Karen L. Pads received the B.S. degree in ma- terials science and engineering from Cornell Uni- versity, Ithaca, NY, in 1984.
She first worked as a Research Engineer at Raytheon Research Laboratories in Massachu- setts. She joined ARCO Solar in 1986 as a mem- ber of the Advanced Research Group focusing on the growth of CIS and performance of CIS de- vices. She has since made significant contribu- tions to the improvements in CIS device and mod- ule technology. She is currently a Research
Engineer and directs the Polycrystalline Materials Deposition Laboratory involved with research and process development of CIS and related film deposition. She is a coauthor of several technical publications related to CIS research and module development.
Dave N. Pier (S’84-M’85) received the B.A. de- gree in physics from Carleton College, North- field, MN, the B.S. degree in electrical engineer- ing from Columbia University, New York, NY, and the M.S. degree in materials science from Stanford University, Stanford, CA.
He held positions at the Litton Industries Guid- ance and Control Systems Division and at the Rockwell International Science Center. He joined ARCO Solar’s Device Measurement group in 1984 as part of ARCO’s summer student employment
program. After finishing his-master’s program, he returned to ARCO Solar in the Advanced Measurements group. He is currently a Senior Research Engineer and manages a group responsible for transparent conductor thin- film processing and research.
