# Presentation: 657818

## Technology in Support of Thin Film CdTe PV Module Manufacturing

- Peter Meyers, Anke Abken, Eugene Bykov, Douglas Dauson, Roger Green, Upali Jayamaha, Rick Powell, Syed Zafar

**First Solar, LLC**
**Perrysburg, OH 43551**
**NREL Subcontract RDJ-2-30630-20**

## First Solar Overview

- _Background_
- Founded in January 1999 to commercialize an advanced technology process for producing cost effective solar modules.
- _Operations_
- First Solar has approximately 250 associates:
- Manufacturing and Process Development – Perrysburg, Ohio USA
- Product Sales and Service – Mainz, Germany
- Corporate Offices and Product Marketing – Phoenix, Arizona
- Strategic Planning Office Europe – Berlin, Germany
- _Projects_
- Over 100 projects in operation around the world.
- _Investment_
- Over $140 million USD has been invested in First Solar since its founding.

## Strategic objective

- Address the opportunities in the  solar industry in the near term to reach “critical mass”
- Create a large, sustainable market for solar electricity by greatly reducing the cost of solar electricity – become “subsidy independent”
- Reduce dependence on scarce natural resources and curtail greenhouse gas emissions to improve our environment

- Reduce the cost of solar electricity to a level that is economically attractive to electricity consumers

## Standard Product

- Advanced CdTe thin film design produces high energy across a wide range of climatic conditions with excellent low light response and temperature coefficient
- Proven to perform as predicted with a high Performance Ratio (PR)
- Frameless laminate is robust, cost effective and recyclable
- Independently tested by leading US and European institutes and certified for reliability and safety
- TÜV Safety Class II
- Certified to IEC 61646
- CE Mark
- UL 1703

- For more details see - www.firstsolar.com

## Successful Solar Projects

- 1.25 MW
- Dimbach, Germany
- Project Developer: Blitzstrom

## Successful Solar Projects

- 170 kW
- Mainbernheim, Germany
- Beck Energy

- 190 kW
- Memmingen, Germany
- Project Developer: Solarstrom AG

## .. and a personal favorite

- Al and Mary Compaan home in Sylvania, Ohio*
- 4.3 kW of grid-connected thin film CdTe PV modules
- Al commutes with a 1982 GMC S-15 pickup convertedto a battery-powered electric; since the batteries arecharged from the house electricity, the truck is alsosolar-powered!

- *For more info see – http://home.earthlink.net/~alcompaan/

## 20 MW/yr and growing fast

- March 2005	Decision finalized to expand the Perrysburg facility by adding
- 		two parallel 25 MW/yr production lines
- May 2005 	Broke ground on the new 50 MW/yr production facility
- August 2006 	Both lines at full capacity levels
- 2007	Annual Production Capacity at 75 MW
- Future	Plans are being considered for manufacturing expansion in Europe

- Groundbreaking for new production facility, May 2005

## Power Performance

- TEP Array 3 – Tucson Electric Power - Springerville, Arizona
- Longest running, commercial array (commissioned May 2003)
- After initial 3% drop, array has maintained a stabilized degradation rate of approximately -0.5%/year, after adjusting for seasonal variation.

## Cost Reduction Roadmap Defined

- First Solar has developed a detailed cost reduction roadmap for reducing total system cost by partnering with others in the supply chain.

## First Solar’s Thin Film Technology - Best PV to Improve the Environment

- CdTe is sourced from zinc mining waste, which is unavoidably present in the environment
- “Up-Cycling” mining waste and making use of existing cadmium waste into a safer, more environmentally productive use
- A closed loop manufacturing process prevents the release of cadmium into the environment
- Encapsulated in a First Solar module, the cadmium cannot be released into the environment - even by breakage or fire
- CdTe modules are reclaimed at end of life
- An effective recycling process extracts cadmium from spent modules and production waste for use in new products.
- Cadmium can be tracked anywhere in the world

- _Bringing Cadmium into Controlled Closed-Cycle-Use_

## Pre Funded Reclamation & Recycling Program

- First Solar reclaims and processes manufacturing scrap and spent modules at the end of their useful life, through a pre-funded program.
- For every module it sells, First Solar sets aside funds to cover anticipated costs for module return and recycling at the module’s end-of-life.
- End-of-life assumptions are reviewed and funds are reinvested periodically to assure full coverage of anticipated module return and processing costs.

## CdTe May be the Most Environmentally Sound Technology for Solar Power Generation 

- Years of energy production required to repay energy consumed in manufacturing.
- Multi-crystalline silicon shows ‘worst case’ and ‘best allocation’ scenarios.
- Typical installations compared to PVACCEPT demonstration objects

- Data from PVACCEPT European Commission study under the 5th Framework Program. February, 2005

- Energy Payback Time (EPBT)

- mc-Si: 	7.8 yrs (worst case average)
- mc-Si: 	3.1 yrs (best allocation average)
- CIS:    	2.8 yrs (average)
- CdTe:  	1.1 yrs

## Technology Development supportsongoing production scale-up

- First Solar uses highly automated assembly lines to convert glass plates into finished solar modules.
- Production lines all produce a common module product, enabling economies of scale to be achieved in raw materials and operating procedures.
- Replication of production lines results in increased module production.

**Notes:**
CdTe is a direct bandgap semiconductor, which enables it to convert solar energy into electricity more efficiently (i.e., more watts per kg of material) than the indirect bandgap semiconductor materials used historically.The energy bandgap of CdTe, at 1.45ev, enables it to convert more energy from the solar spectrum than the lower energy bandgap materials (1.20ev) used historically. As a result, CdTe is capable of converting solar energy into electricity at an efficiency rate comparable to historical technologies with about 1% of the semiconductor material requirement.CdTe will generally produce more electricity under real world conditions than solar modules with comparable powered ratings.Solar cells become less efficient at converting solar energy into electricity as their cell temperatures increase. However, the efficiency of CdTe is less susceptible to cell temperature increases, enabling CdTe solar modules to generate relatively more electricity under high ambient (and therefore high cell) temperatures. CdTe also absorbs low and diffuse light and more efficiently converts it to electricity under cloudy weather and dawn and dusk conditions where conventional cells operate less efficiently. As a result, CdTe will generally produce more electricity under real world conditions than conventional solar module with similar power ratings.CdTe permits simple device structures and processes, leading to low cost production.  The robustness of CdTe enables relatively simple device structures and production processes. High performance modules are achieved with single junction, polycrystalline devices. Automated high throughput production processes have been employed successfully with CdTe, without the need for expensive clean rooms or other expensive specialty equipment.
Abundant raw CdTe material to support high volume production and demand.CdTe is made by transforming cadmium and tellurium into a stable, inert semiconductor. Both elemental materials are produced as byproducts of mining processes (primarily zinc mining and copper refining) and present in abundant quantities to support multi-GWs of annual production 

These attributes have lead the National Renewable Energy Laboratory in Golden, Colorado to recognize CdTe’s potential for achieving the lowest production costs among current thin film technologies. (Photon International, November 2004, page 50). CdTe module costs well below $1.00/Wp have been predicted by NREL and others. 

## AFCW (Advanced Front Contact Window)

- Expectation is that a high resistivity “buffer” layer will enable use of thinner CdS and therefore higher Jsc
- Best cells (without buffer layer) show peak in Efficiency vs. Jsc at ~23 mA/cm2
- Modules peak at lower overall Jsc due to sensitivity to thin spots in CdS
- Results to date with buffer layer modules do not show shift in peak efficiency vs. Jsc
- Highest efficiency buffer layer module - 9.71%.

## VTD - Vapor Transport Deposition

- The key enabler for low-cost, high-throughput manufacture is rapid
- deposition of high-quality semiconductor films:

**  ****Gen I semiconductor   **
**  ****deposition system **

**Vapor Transport Distributor****(artist’s conception for R&D 100 award)**

- Semiconductor film deposition time is less than 15 sec
- Patented vapor transport process
- Deposition throughput is 1.5m2/min
- High quality of semiconductor films made possible by high temperature deposition, which is made possible on low-cost substrates by patented center support of glass during deposition.

## VTD-2 Even a great design can be improved

- VTD-2 Advanced distributor developed during this program is a fundamentally new design developed around a completely new operating principle (patents applied for)
- Films more uniform across a plate, more uniform plate-to-plate with a run, and more uniform run-to-run
- Simplified control
- Improved material utilization by reducing overspray
- Expect that VTD-2 will become the new “standard” distributor

-  Improved powder feed
- Powder “pulses” in input feed result in variations in film thickness – sensitive primarily for CdS films
- Advanced feeders eliminate powder pulses
- Patent applied for

## Distributor Computer Simulation – lower tier subcontract to Colorado School of Mines*

- CSM researchers developed detailed computer simulation of distributor operation
- Provided valuable insight into distributor operation
- Validated computer simulation through demonstration of good agreement with experimental results

*** ****	**Robert Kee, Jean Pierre Delplanque and Mark Pavol, “Direct integration of solid-precursor powders into chemical vapor deposition systems”,  lower tier subcontract under NREL RDJ-2-30630-20, awarded to Colorado School of Mines.

- Developed a set of uniformity metrics expected to influence film characteristics and thereby device performance
- Performed a Taguchi style designed experiment to evaluate the effect of changing experimental parameters that would otherwise be prohibitively costly or time consuming to evaluate

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## 3LM- 3rd Level metrics*

- Small changes in performance area a large concern
- Key to limiting process variation is measurement and control of key work-in-progress (WIP) physical, electrical, optical or chemical properties
- Each process step has an “ideal function” – challenge is:
- Identify key metric
- Confirm relevance
- Affects product performance
- Controlled by process
- Quantify acceptable process latitude
- 6 Sigma methodology
- Implement into production
- Statistical Process Control (SPC)

- *1st level=Module Power; 2nd level=I-V parameters, e.g. Jsc, Voc, FF; 3rd level=physical, chemical, electrical and optical properties

## 3LM- Reflectometer for CdS thickness 

- Dependence of reflection spectrum is a well-established theory, but practical implementation is problematic
- Key breakthrough was development of empirical model to interpret experimental spectra that was robust against process variation
- Model and instrumentation underwent rigorous statistical analysis before being certified for production

- SPC chart

**Syed Zafar monitors CdS reflectometer as it maps CdS thickness of production CdS/CdTe plate**

## ALT – Accelerated Life Test

- ALT objective is development of an Accelerated Life Test that enables timely monitoring of production line performance and process optimization
- Focus on “stress” of illumination, electrical bias and temperature; Elevated temperature is the primary accelerating factor
- Working Model
- Illumination and electrical bias affect the electron and hole quasi-Fermi levels and therefore the local electrochemical steady state energy
- Premise is that changes in performance are caused by defect mutation, ion migration and diffusion
- There is no one mode of changed device performance  as electrical properties of main junction, bulk film and back contact can be indepenently affected
- Steady state performance depends on stress history

## ALT – cont.

- Good reproducibility within controlled sample populations has been achieved
- Correlation of results is lower with more varied population and test device structures
- Degradation of EVA at elevated temperature introduces limitations to application of ALT to laminated modules
- Development of an effective ALT remains an important goal of the CdTe PV community

- Distribution of Relative Stabilized Stressed Efficiency for Various Stress Tests and Populations
-   Sister Plates, Std. LS      2.5%
-   Strips, single Plate, ALT  1.0%

## EH&S Environmental, Health and Safety

- Working to improve an unblemished record
- Dust-producing processes modified and automated to reduce exposure of personnel to Cd-containing dust
- Removal of ‘wrap-around” deposition onto “sunnyside”
- Former process – operators hand-polish of sunnyside
- Current process – in-line chemical stripping
- “Edge-delete” – removal of all films 1.5 cm border around module to provide moisture barrier and ensure electrical isolation
- Former process – operators grit-blast in glove boxes
- Current process – in-line grit blasting with effective collection of grit and dust
- Hazardous waste from disposal of off-spec modules eliminated
- Former process – plates/modules crushed, Cd-containing wastes separated from glass and other solids and processed into “cakes” disposed of as Hazardous Waste
- Current process – modules are shredded and sent to Cu smelter where Cd is recovered and recycled

## Summary

- With plants under construction to increase capacity to 75 MW/yr by 2007, First Solar is one of the fastest growing companies in the PV industry
- Proactive EH&S program, pre-funded module reclamation & recycling program, and low energy payback time make First Solar CdTe PV one of the “greenest” PV technologies
- Programs are in place to reduce costs and thereby enable further market growth
- Technology development advances
- Progress toward efficiency improvement through AFCW
- Improved performance, film uniformity, and material utilization through VTD distributor and advanced powder feed (five patents applied for)
- Improved process control through WIP 3LM metrics
- Improved EH&S procedures
- Progress toward improved ALT