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Department of Mechanical Engineering

Fort Collins, Colorado 50523

970.491.6559

04-21-06

Ken Zweibel, MS 3212

National Center for Photovoltaics

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, Co. 80401

Dear Mr. Zweibel:

This is the first quarterly report of phase II of our research under the
current Thin Film Partnership Program (Subcontract No. XXL-5-44205-02 to
Colorado State University). A brief summary and details of our work are
given below. This report is in fulfillment of deliverable D.2.1 of the
subcontract statement of work (SOW).

# Summary

During this quarter, we have progressed on the tasks outlined in our SOW
for Phase II. A fixture for automated cooling of the substrate in vacuum
has been designed, fabricated, installed and tested. This is needed for
optimum processing of the back contact. Large area devices in the form
of strips (\~0.5 cm X 8 cm.) have been fabricated and tested at NREL.
Efficiency of 10.9% has been measured. The air-to-vacuum-to-air seals in
the pilot system have a glass filled teflon liner. These liners have
experienced wear and this results in scraping of the glass substrates in
the seal. Improved liners have been designed and fabricated and are
being installed in the system. Based on our current progress, no
difficulties are anticipated in successfully completing the future
targets outlined in the SOW.

A prototype production system to process 16.5x16.5 inch substrates
continues to be advanced. This activity is supported by another program
from DOE-EERE and cost shared by National Starch and Chemicals (NSC). We
are also in discussion with a reputed company to form a strategic
partnership to manufacture large volumes of CdTe PV based on our
technology. Numerous documents have been submitted to this group for
evaluating our technology. These discussions have advanced
significantly.

**[Detailed Description of the Results:]{.underline}**

[1. Cooling Substrates in Vacuum.]{.underline}

The pilot system for processing 3.6 x 3.1 inch substrates has been
modified to more closely simulate the back contact processing suitable
for actual industrial manufacturing. With the old configuration of the
pilot system, the Cu back contact process head is located immediately
after the CdCl~2~ treatment heads. If the substrate enters the copper
process at too high a temperature, the resulting devices have a high
series resistance. To avoid this, a pause to cool the substrate was
introduced in the old configuration of the pilot system. After a nominal
3 hour wait, the substrate motion direction is reversed and the now cool
samples are exposed to a vapor flux of the Cu compound followed by
annealing. This completed the formation of the Cu containing back
contact in the old configuration. The old configuration is not suitable
for large volume manufacturing.

To simulate the Cu back contact process for actual production the pilot
system has been lengthened to allow fabrication of devices without the
pause and change in substrate motion (\"all forward\" process). The
modified pilot system would also allow processing of devices in a manner
which emulates a continuous production system. An automated system for
cooling substrates in vacuum has been designed, fabricated, installed
and tested. The cooling fixture was tested with automated substrate
movement. The substrates were heated to 200 C and after 4 minutes of
radiation cooling were cooled with the fixture to 26 C in two minutes.
The results indicate that an adequate cooling rate can be obtained to
maintain a cycle time of 2 minutes. The measurements of substrate
temperatures were performed with infrared sensors. The modified pilot
system will enable precise definition of conditions for all the
semiconductor processing steps (including the back contact) needed to
fabricate high efficiency, stable CdTe devices. This process definition
will be implemented in the 2 MW/yr. production prototype system for 16.5
x 16.5 inch substrates. The principle of the cooling process has been
described in our earlier reports.

[2. Modification of the Seals:]{.underline}

The pilot system for processing 3.1 X 3.6 inch substrates has a
differentially pumped air-to-vacuum-to-air seal that has a glass filled
teflon liner for supporting the belt. This system has been operational
since 1997. This system has been used to process nearly 10,000
substrates. The wear in the liner is causing the substrate to contact
the seal and this leads to pinholes. In addition, the adhesive bond
between the teflon liner and the aluminum support plate has also
degraded. A new teflon liner with improved attachment to the aluminum
support plate has been designed and is currently being fabricated and
will be tested .

[3. Large Area Devices:]{.underline}

Many large area devices in the form of narrow strips of \~0.7 cm. wide
and 4 sq. cm. total area were processed to study the performance of
these devices. The widths are representative of cells in modules.
Devices were tested at NREL and the efficiency of 10.88% was measured
and efficiency of 11.1% was also measured independently at IEC. These
measurements indicate that module efficiency of 10% based on active area
is feasible with our technology. The 10% module efficiency was utilized
in the cost calculations developed for our technology. These
calculations were sent to you earlier and summarized in the AVA Tech.
recent team presentation.

[4. Higher Efficiency]{.underline}

We have demonstrated NREL verified efficiencies of 12.44% on unmodified
Pilkington Tech15 glass. In order to obtain higher efficiencies, low
iron sodalime (white glass) glass plates have been obtained and cut to
size suitable for our pilot system. Fifty substrates have been sent to
Sierratherm for APCVD (atmospheric pressure CVD) coating with TO:F. The
coated substrates have been received and have been given to Professor
Sites\' group for optical studies. Coated samples have also been
received from Solaronix. Deposition experiments with these substrates
will be performed soon. The APCVD process is suitable for low cost high
volume processing. After the current batch of samples, the use of
barrier layer deposited by APCVD and other methods will be investigated.
Discussions have been held with Pillkington and PPG and they have
indicated that they may produce white glass with \"TEC\" type tin oxide
coating in the future.

[5. Collaborative Studies and Other Activities:]{.underline}

During this quarter, the following collaborative activities were
conducted:

1)  19 cells were provided to Alan Davies (Prof. Sites\' group) and
    these cells were stress tested and it was shown that at optimum
    processing, good stability can be obtained. Thsi was presented at
    the CdTe Team Meeting.

2)  Many interactions with Larry Olsen of PNNL regarding the application
    of CdTe devices for another application have occurred.

3)  Graduate student Tushar Shimpi graduated with a MS degree and Jim
    Sites served on his committee.

4)  Two presentations were given at the CdTe Team meeting.

5)  Twenty slides on our research were provided to Ramesh Dhere of NREL
    for his tutorial at the IEEE PV Conference.

6)  Marc Landry and Ramesh Dhere (both of NREL) and visitors from Ziyax
    Corp. were given a tour of our laboratory and possibilities of
    collaboration were discussed. Other visitors include: Steve Johnson,
    researchers from PPG, etc.

If you have any questions, please do not hesitate to call the laboratory
at (970)-491-8411. Thank you.

Sincerely,

W.S. Sampath

Associate Professor

Colorado State University

CC: C. Lopez