CSBurton TO41

 FINAL DRAFT 

 

PFC-Emissions during 

Photovoltaic (PV) Cell 

Fabrication: A Scoping Report 

Draft Report 

April 2006 

Prepared for: 

ICF Consulting 

1725 Eye St., N. W. 

Suite 1000 

Washington, D. C. 20006 

 

Prepared by: 

C. Shepherd Burton, Ph. D. 

2047 Huckleberry Road 

San Rafael, CA 94903 

(415) 902-5504 

ICF Subcontract No. 22J00074 

ICF EPA Contract: GS-10F-0124J 

ICF Contract No. 023015 

Task Order 041 
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Table of Contents 

1. Introduction...........................................................................................................1-1

2. Solar cells—how they work, their efficiency, cost and size and the prospect for 

growth....................................................................................................................2-1

2.1. How solar cells work.................................................................................................2-1

2.2. Power conversion efficiency.....................................................................................2-2

2.3. Cost and the economic prize of solar electricity .......................................................2-2

3. PV Cell Manufacture .............................................................................................3-1

3.1. Links to semiconductor and flat panel display manufacturing..................................3-1

3.2. PV Cells fabricated with x-Si ....................................................................................3-2

3.3. PV Cells fabricated with amorphous-Si....................................................................3-3

3.4. Emerging PFC-using fabrication technologies .........................................................3-5

3.5. Potential PFC emissions from existing and emerging PFC-using technologies.......3-6

4. Global PV Industry: Installed Capacity, Growth, Regional Shares of Production 

Capacity, PFC Emissions and Equipment Suppliers.........................................4-1

4.1. PV production growth...............................................................................................4-1

4.2. An initial estimate of uncontrolled, global PFC emissions for 2004 and 2010..........4-3

4.3. PV-cell equipment manufacturers ............................................................................4-6

5. PFC Emission Control Technologies..................................................................5-1

6. References ............................................................................................................6-1

List of Figures 

Figure 1. Forecast of global PV-cell production, MWp................................................................................4-1 

Figure 2. Country shares of installed PV capacity..........................................................................................4-2 

Figure 3. Trends in regional PV production: 1995-2004................................................................................4-2 

Figure 4. Trends in regional PV-cell production, m2, 1995-2004..................................................................4-3 

List of Tables 

Table 1. Reported status of PFC-use during fabrication of some PV cells................................................3-9

Table 2. PV-cell equipment manufacturers.................................................................................................4-8 
Table of Contents 

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1. Introduction 

Similarities between the photovoltaic (PV) industry on the one hand, and the semiconductor and 

active matrix liquid crystal display (AMLCD) industry on the other, prompt concerns about the 

potential for uncontrolled atmospheric releases of high GWP greenhouse gases (GHG) during 

PV fabrication. Those similarities include use of (1) silicon and thin-film technologies (TFT), and 

(2) sustained high growth rates. 

As this report will reveal, however, the analogy of the PV industry to the semiconductor and 

LCD industries cannot be pressed too far at this time: PV-cell technology, manufacturing 

processes and the associated infrastructure across the PV-industry lack the semiconductor and 

LCD industries’ unity of technologies (e.g., CMOS1

 and TFT technologies) as well as tight 

integration of R&D and manufacturing technology planning (e.g., International Technology 

Roadmap for Semiconductors and FPD Roadmap). The result is a relatively fragmented PV 

industry compared to the tightly coordinated semiconductor and LCD industries.2

 All three 

industries are highly competitive and aggressive. 

This scoping report, after first summarizing the workings, cost, growth rate and manufacture of 

solar cells, examines actual and potential emissions of high-GWP GHG gases during PV 

fabrication. The report (1) identifies the processes that use high-GWP gases, (2) identifies 

emission factors (utilizations and/or emission/unit activity); (3) prepares preliminary (worst case) 

estimates of current emissions for US, Japan and Europe; (4) provides published estimates of 

industry growth rates; and (6) describes available emission reduction technologies. 

Information for preparing this report was obtained from searching the internet. Budget 

constraints prevented the author from contacting experts in PV manufacturing. 

 

1 CMOS technology refers to complimentary metal oxide semiconductors. CMOS is the most widely used technology for 

fabricating the transistors in today’s integrated circuits (IC). CMOS technology is in almost every electronic product from 

handheld devices to mainframe computers. CMOS’ popularity stems from its relative power demand; CMOS transistors 

consumer almost no power until switched. 

2 It is also worth noting that semiconductor and LCD-TFT technologies support and enable a seemingly ever expanding array of 

products that offer buyers a wide range of value proposition and, in turn, can support very large investments. The 

corresponding PV-technologies, however, support one product—the solar cell—whose value seems highly constrained by the 

cost of conventional means for generating electricity. 
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2. Solar cells—how they work, their 

efficiency, cost and size and the prospect 

for growth 

2.1. How solar cells work 

Solar cells exploit the photovoltaic effect exhibited by semiconductor materials. When light of an 

appropriate energy (or color) strikes an electron attached to a semiconductor atom in the crystal 

lattice, the electron is freed to move in the lattice, which creates a “hole” (a region with a net 

positive charge) that can also move. These light-generated negative (n) and positive (p) charges 

are the constituents of electricity. 

This process is described as the creation of mobile electron-hole pairs (or charge carriers). 

These charge carriers are then separated by an internal electric field formed when 

semiconductors with different electrical characteristics come into contact. The electrical field 

drives positive and negative charges in opposite directions. That movement of charge through 

an external circuit is electricity (Landsberg, 2002). 

While there are several ways to form an electric field in crystalline silicon, the most common is 

to slightly alter the structure of an atomically pre-altered form of the silicon crystal. This 

technique, known as doping, introduces an atom of another element (the dopant) into the 

atomically pre-altered silicon crystal to modify its electrical properties. This pre-altered form of 

silicon is called p-type, and will be described shortly. 

The most common dopant in photovoltaic cells is a phosphorous atom, which occupies the 

same place in the lattice that was formerly occupied by the silicon atom that was replaced. 

However, phosphorous has one more electron than silicon that is free to move. If there are 

many phosphorous atoms substituted for silicon there are many additional electrons that are 

free to move. This type of silicon is called n-type silicon because it has more (or extra) negative 

carriers (electrons) than normal silicon. The most common method of phosphorous-substitution 

is to apply the top layer of crystalline silicon with phosphorous and then heat the surface to force 

phosphorous to diffuse into the silicon crystal lattice. Other methods include gaseous diffusion, 

a liquid spray-on method and ion implantation (where high velocity phosphorous atoms are 

targeted at the crystalline silicon surface). 

N-type silicon cannot form the electric field by itself, which is why the doping process starts with 

an atomically pre-altered form of silicon. This pre-altered form is a p-type silicon. P-type silicon 

consists of silicon that has been doped with boron atoms during the manufacture of the silicon 

crystal. When boron takes the place of silicon in the lattice, an electron is missing creating an 

electron hole. In this p-type silicon, then there are many more positive charges (or holes) than 

free electrons, so there are extra positive charge carriers.3

 

 

3 It should be realized that n-type and p-type silicon are both electrically neutral: each material contains an equal number of 

negatively charged electrons and positively charged protons. 
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It is the presence of layers of n-type and p-type silicon materials that creates the electric field. 

The field is strongest where the p-type and n-type silicon are in contact—the p-n junction. The 

strength of the field (the greater the difference in semiconductor electrical properties) is 

governed by the amount of dopant in the silicon. At the junction, the extra charge carriers—

electrons in n-type and holes in p-type silicon—respond to the electric field the greatest. 

Electrons are attracted to and holes are repelled by the internal electric field. 

The p-n junctions in PV cells are constructed to maximize the flow of charge carriers across the 

junction before they can recombine, which would result in no current flow. It is the construction 

of p-n junctions, including doping and many other factors that determine the efficiency of a PV 

cell to convert solar power into electrical power.4

2.2. Power conversion efficiency 

The dominant consideration in PV manufacture is providing the highest solar-to-electricity 

conversion at the lowest manufacturing cost. 

The power conversion efficiency of a solar cell—the amount of power produced per solar power 

input—and the cost per watt produced, determines the commercial utility of solar cells. 

Efficiency is a ratio of the electric power (watts, We) output to light power input. Near the Earth’s 

equator at noon on a clear day, the solar radiation is approximately 1000 Ws/m2

 (Ws denotes the 

power from the sun in watts.). A solar cell of 1 square meter with an efficiency of 10 percent 

can, therefore, power a 100 We light bulb (=0.1 We/Ws x 1000 Ws). 

The average conversion efficiency in popular solar cells (using the semiconductor silicon) is 13 

percent, and varies depending on the semiconductor material used and method of fabrication 

(Wilcox et al., 2004). (The maximum theoretical efficiency for a semiconductor is approximately 

30 percent (Landsberg, 2002). For commercial devices, efficiencies vary between 5 and 17 

percent (Wilcox et al., 2004). 

Decreasing the cost per Wp generated in the shipped system is a driving commercial metric of 

the industry. Wp refers to peak watts produced, which occurs at mid-day. Increasing conversion 

efficiency at the smallest possible increase in manufacturing cost—so that the cost per Wp

generated is competitive with conventional sources of electricity—is one of two major R&D 

initiatives of the PV industry. The second major R&D initiative seeks the greatest reduction in 

manufacturing cost with the smallest (or no) loss in conversion efficiency. 

2.3. Cost and the economic prize of solar electricity 

The economic prize the solar industry seeks is penetration of the grid-connected electricity 

generation market5

. Tying into the grid offers decades of sustained double digit growth. But to 

compete, the cost of PV systems must drop substantially. 

 

4 In PV cells that use thin-film technology, p-n junctions are replaced with p-i-n junctions, where i refers to the intrinsic layer, 

which is located between the p and n layers of the p-n diode. More about this PV cell structure will be described later in the 

section on fabrication of thin-film PV cells.

5 The term grid-connected refers to both consumer and utility sides of the meter. 
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Currently, the average installed price for PV systems is $4/Wp, which is heavily weighted toward 

cells manufactured using silicon wafers. A typical residential system, designed to provide 

2.5kWp, would cost, on average, $10,000 and occupy approximately 19 m2

 or more of roof area 

depending on sun exposure assuming a power density of 130 Wp/m2

 (=12 Wp/ft2). A typical 

utility central plant, estimated at 5MWp, would cost $20M and would occupy a PV area of 

approximately 38,500 m2

, using the same power density for residential and commercial 

applications. 

Numerous reports extol the virtues of and opportunities for PV cells for producing electricity. 

Since the mid-1970’s, average efficiencies of commercial PV cells have more than doubled, 

from 5.8 to 13 percent, although since 1990 the rate of improvement appears to have slowed to 

approximately 0.07 percent/year (Wilcox et al., 2004). Between the mid-1980s and 2005, the 

installation price of high power band (>70 W) solar modules dropped from about $30/Wp to 

$4/Wp today (Maycock, 2005). 

Associated with these improvements in efficiency and reductions in cost, is a 60-fold increase in 

annual, global PV-module shipments, from approximately 20 MWp shipped in 1982 to 1200 MWp

projected shipments in 2005 (Maycock, 2005). Of the total projected shipments for 2005, 

approximately two-thirds are for the grid-connected market, with the remainder divided among 

consumer, communication/signal, commercial and off-grid residential and rural markets. Based 

principally on maintaining current trends in cost reductions (approximately 5 percent per year), 

global shipments for 2010 are projected to reach 4000 MWp, with approximately 75 percent of 

those shipments expected to serve the grid-connected market (Maycock, 2005). 

Notwithstanding its “green label”, an ongoing debate among energy policy makers is whether 

solar electricity is a boutique industry that is suitable in certain applications or whether it can 

become an essential part of electric generation, like natural gas, nuclear or coal. Even at 

compound annual growth rates of 30 percent since the late 1990s, solar electricity is far from 

making a significant contribution to global or US energy supply (Maycock, 2005). 

The prize for the solar industry—and the prize that attracts investors and that encourages state 

and federal policy makers to continue and to expand existing forms of policy and financial 

support for PV industry expansion— is penetration of the grid-connected electricity generation 

market. The market is huge, providing the solar industry and its investor’s decades of sustained 

high double digit growth. 

For example, PV systems shipped in 2004 made-up roughly 0.1 percent of US grid-generated 

power, after two decades of double-digit annual growth rates. The annual value of that 0.1 

percent share was roughly $700 – 800 million (Chaudhari et al, 2004). At lower installation 

costs, say in the range $1 to $1.25/Wp (a very aggressive price reduction of 75 percent below 

the current $4/Wp price), Chaudhari et al. show that, for only US roof-top applications, 

penetration rates could reach approximately 1.6 percent by 2010, valued at $13.10 billion and 

divided almost equally between residential and commercial installations. 

The principal determinant of this increased penetration is faster payback, which accelerates as 

installed prices drop (Chaudhari et al. 2004). While a 75 percent price reduction is aggressive 

(and probably unachievable with time to appreciably affect 2010 shipments), other assumptions 

made by Chaudhari et al. that govern PV demand are neither conservative nor optimistic; their 

and similar analyses have attracted inventors and investors, raising more that $120M in the US 

since 2001 (SF Chronicle, 11 July 2005). 
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3. PV Cell Manufacture 

To attain the grid-connection prize, the PV industry is pursuing reductions in production/material 

costs; improvements in PV-cell yields, efficiency (higher power densities) and lifetime; increased 

fabrication productivity/throughput; or some combination thereof. Available reports suggest the 

PV industry is pursuing many tracks, with, except for status-quo—PV cells fabricated with 

crystalline silicon—no clear favorite yet evident. 

These multiple tracks are grouped, for the organizational purposes of this report, into two more 

or less homogeneous categories: improving the cost-performance of crystalline silicon (x-Si) 

technology (currently the dominant technology) and thin-film technologies (currently an 

emerging technology) (Maycock, 2005). Crystalline Si technology accounted for approximately 

90 percent of global PV shipments in 2004 (Maycock, 2005). 

Both x-Si and thin-film technologies possess, as often cited by their advocates, synergies with 

semiconductor and FPD fabrication methods (Roca and Carabe, 2003; Wohlgemuth et al., 

2003; Soppe et al., 2003; Shah et al., 2004; Agostinelli et al., 2004; Agostinelli et al., 2005; 

Bosch et al., 2004; Janz et al., 2004; Rentsch et al., 2005a; Rentsch et al., 2005b; and 

Kenanoglu et al., 2004). Despite the advocacy there is little evidence that the case has been 

heard and the technologies adopted. 

3.1. Links to semiconductor and flat panel display 

manufacturing 

Commercial PV fabrication grew out of 1980s microelectronics technology (the era of 4 and 5 

inch wafers)6

, relying on technology for manufacturing highly purified (and costly) crystalline 

silicon wafers as well the microelectronic industry’s batch, wet chemical technology for 

fabricating p-n diodes and electrodes. This linkage produced and continues to produce an 

upward pressure on PV costs at current PV-production volumes. 

The high-purity silicon required for IC fabrication is unnecessary for PV fabrication but the PV 

industry is still too small to support breakthrough, cost-reducing alternatives. While the cost of 

high-purity crystalline Si wafers used in chip manufacturing is spread across hundreds of chips, 

just one PV cell can be produced for each wafer, assuming 100 percent yield; the result is that 

40 – 50 percent of each solar cell is the wafer cost (Wilcox et al. 2004). In addition, the cost of 

modern semiconductor-device fabrication equipment also seems beyond the economic reach of 

PV manufacturers at current PV-production volumes. Nevertheless, the link to the 

microelectronics industry continues, with the PV industry seemingly considering wide adoption 

of plasma etching and plasma enhanced chemical vapor deposition (PECVD) technology. 

That wafer cost would limit reductions in PV fabrication cost led the PV industry to seek 

alternatives, including moving to thinner wafers, to lower quality wafers as well as to using 

alternative methods for manufacturing crystalline silicon (e.g., as-grown sheets of silicon or 

 

6 Four inch (100 mm) wafers were introduced in 1975; 5-inch (125 mm) wafers were introduced in 1979. PFC-use in 

semiconductor manufacturing was commercially introduced toward the end of the 6-inch (150 mm) wafer era and the first third 

of the 8-inch (200 mm) wafer era in 1988 or so. 
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ribbons of silicon).7

 In addition, some manufacturers seem to be moving away from what are 

mostly batch processes to more in-line, integrated methods for PV-cell fabrication on x-Si as a 

way to lower overall cell cost (Phylipsen and Alsema, 1995; Wholgemuth et al., 2003; Soppe et 

al., 2004; Shah et al., 2004; Wolke et al., 2005). 

Researchers, since the 1980s, have also studied thin-film solar module concepts, i.e., solar 

panels using thin-films (such as amorphous-Si (a-Si), CdTe and Cu (In,Ga) Se2 (CIGS)) 

deposited on large, low-cost substrates (glass, stainless steel or aluminum). These researches 

extol the manufacturing synergies between thin-film solar panels and AMLCD panels, which 

utilize a-Si thin-films deposited on glass (Shah et al., 2004). Others are pursuing not only new 

kinds of (proprietary) thin-films but also new substrates (plastic) and new methods for applying 

(roll-on printing and painting) the thin-films to those substrates (Nanosolar, 2005). 

Still other researchers tout the advantages of the PV industry adopting the dry processing, highthroughput processes of microelectronic manufacturing (Agostinelli et al., 2004; Agostinelli et 

al., 2005; Rentsch et al., 2005a, 2005b and 2005c), which has only been adopted in limited 

ways in PV cell manufacture using x-Si (Phylipsen and Alsema, 1995). 

What is evident is that while increasing current global production at annual rates of 30 percent 

and while reducing average panel costs at 5 percent per year, the PV industry is pursuing many 

alternatives in search of breakthrough cost-reductions to attain the prize of grid-connection. That 

pursuit appears relatively complex and capital-starved despite evidence of relatively large 

government support. 

The remainder of this section describes the essential steps in PV cell fabrication, first using x-Si 

technology and then a-Si technology. In each case emphasis is given to the actual or potential 

use of high-GWP gases during PV cell manufacture. 

3.2. PV Cells fabricated with x-Si 

Fabricating PV cells using x-Si technology starts with p-type (boron-doped) Si wafers. To make 

the n-p junction, phosphorus is diffused into the wafer. Then the back and front aluminum 

contacts are usually deposited by screen-printing and then fired. At the end of the process, or 

just after phosphorous diffusion, a single passivation and anti-reflection coating is deposited on 

the front (incoming sunlight) side of the cell (Phylipsen and Alsema, 1995; Lossen et al., 2005). 

A typical x-Si production line follows 7 major steps: 

 

7 For example, the PV industry is a large and growing user of polycrystalline silicon (consisting of multiple small crystals rather a 

single cystral) from which monocrystalline silicon wafers are made for fabrication of semiconductor devices. The demand for 

polysilicon by solar cell manufacturers has increased to the point that shortages in 200 mm and 300 mm wafers for 

semiconductor manufacturing are projected for 2006 and possibly 2007 (LaPedus, EETimes, 2005 “Polysilicon shortages to 

cause wafer price increases”). Recent reports describe a constrained supply of polycrystalline silicon such that PV production 

in 2006 will be but 5 percent above 2005 production levels, compared to recent annual growth rates of 30 – 40 percent (Pichel 

and Yan, 2006). 
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(1) alkaline damage etch repair and texturing8

—damage due to wafer cutting is repaired and 

texturing accomplished using a solution of NaOH (or KOH) and H2SO4; 

(2) emitter (n-type) formation by phosphorous diffusion; 

(3) edge isolation to reduce current leakage (using either plasma [CF4] or wet etching) 

(4) phosphorous silicate glass (PSG, formed during n-p junction formation) etch using a solution 

of HF 

(5) silicon nitride (SiNx) deposition using PECVD (SiNx film provides passivation and antireflection properties to cell) 

(6) screen printing or metallization contacts/electrodes, and 

(7) firing of metal contacts. 

Two reports describe PFC use during x-Si PV-cell fabrication (Phylipsen and Alsema, 1995; 

Alsema et al., 1997). Production-line CF4-usage occurs during step 3. However, CF4-use is not 

universal because of reported plasma damage that lowers panel yield (Pylipsen and Alsema, 

1995). Alsema et al. (1997) reports SF6-use in cleaning PECVD chambers used to deposit SiNx, 

which provides cell passivation and improved light capture through anti-reflection. (Similarly 

formed anti-reflection films are used in the photoresist steps during IC and AMLCD fabrication.) 

It should also be noted that despite many reports describing the increased performance of PVcells that incorporate SiNx films technology, only Alsema et al. (1997) reports SF6 use in 

chamber cleaning. Among all the other reports identified and reviewed in preparing this report, a 

method of chamber cleaning was not described (e.g., Liehr, 2001; Wohgemuth et al, 2003; 

Winderbaum et al., 2003; Shah et al, 2004; and Kumar et al., 2005). However, Fthanakis (2005) 

reported that PECVD chambers are usually cleaned manually9

. Shah et al. does report that yield 

losses due to particle contamination during PV fabrication are not important unlike it is during 

AMLCD and IC fabrication (Small particles can short TFTs in AMLCDs, for example and the 

particle problem during IC manufacture is a major failure mechanism for semiconductor devices. 

However, the presence of particles in PV fabrication would seem to be limited to reducing 

optical properties, which on average might be acceptably small and, if so, not a cause of PV-cell 

failure. Thus, unless in-situ chamber cleaning offers productivity increases, it may be simply a 

cost-ineffective cleaning method.) 

3.3. PV Cells fabricated with amorphous-Si 

Amorphous-Si solar cells, first developed in 1976, offer the advantage of manufacturing entire 

arrays of cells—instead of connecting individual solar cells from silicon wafers onto panels and 

wiring them together to form systems—with a single series of steps on sheets of a low-cost 

 

8 Texturing refers to surface texturization of x-Si to attain improved conversion efficiencies. Surface textures diminish reflections 

losses and cause an oblique coupling of light into the silicon lattice. More net charge-carriers result and cell efficiency 

improves. 

9 A confidential report to the author from a PV manufacture (that uses a-Si technology) boasts of PECVD chamber designs with 

shields around the substrate that captures 99.9 percent of the fugitive film material before it reaches the chamber walls. In 

addition, the report notes that “walls (are designed) to be cold and biased so that very little (fugitive) material deposits...and 

cleaning (when needed) can be accomplished with HCl and hydrogen.” 
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substrate, such as glass, metal or plastic. Vapor deposition methods are used to fabricate 

photodiodes (p-i-n diode) from several micro-thin layers of a-Si alloys on a transparent film of tin 

oxide (called the transparent conducting electrode, TCO), which has been previously deposited 

on the substrate (e.g., glass). The TCO acts both as a conductor and a means for increasing the 

panels light absorption in the red portion of the spectrum. a-Si is one of several thin-film PVfabrication technologies, also called second-generation technologies, and the only one with the 

prospect of using PFCs because the other films do not react with F-atoms. 

The disadvantage of a-Si is reduced and unstable efficiency. Light-induced degradation of aSi:H, known as the Staebler-Wronski effect, degrades performance over time unless more 

complex film structures are used to enhance stabilized efficiency (Wilcox, et al., 2004). In a-Si 

PV cells, the p-i-n junction is employed, with a-Si:H being the i-layer, where light absorption 

occurs. Numerous stacked-cell designs of varying a-Si alloys are used that are intended to 

enhance and stabilize efficiency with light-trapping.10

The roughly 20-year old Chronar process (or some variation of it) seems in wide use for 

producing a-Si solar cells (EPV, 2005; France: National Status Report 2002, available at 

www.oja-services.nl/iea-pvps/nsr02/fra.htm). Which a-Si films (alloys) are used and how they are 

deposited account for most of the manufacturing process variability. EPV (formerly known as 

Chronar), uses “standard deposition techniques to build up” two vertically-stacked paired layers 

of p-i-n diodes (six a-Si layers total); EPV does not describe its standard deposition technique. 

Free Energy Europe and many other a-Si panel as well as equipment manufacturers use a 

plasma enhanced chemical vapor deposition (PECVD) monochamber to fabricate a single p-i-n 

a-Si diode (BP Solar, 200x, United Solar Systems Corp., 200x,, Plasma Quest Ltd, 200x, and 

Applied Film, 2005). However, they do not describe their methods of chamber cleaning. 

Free Energy describes a 7-step process: 

(1) Low pressure chemical vapor deposition of tin oxide (SnO2) on glass 

(2) Laser scribing the tin oxide multi-cell interconnect layer 

(3) a-Si alloy deposition using PECVD to produce the p-i-n junction diode 

(4) Laser scribing of the a-Si alloy layers 

(5) Rear electrode fabrication; aluminum sputtering deposition 

(6) Laser scribing the aluminum layer to form the cell’s other interconnect traces (alternatively 

the aluminum sputtering might be performed using a mask instead of making a blanket film 

and then laser scribing) 

(7) Testing and aging to stabilize efficiency; encapsulation 

What is evident in this process, compared to PV cells fabricated from x-Si, is the absence of 

etching. Just one step might use PFCs: the cleaning of the PECVD mono-chambers. However, 

chamber cleaning is not mentioned, as noted earlier. 

 

10 The term a-Si alloys refers to silicon-carbon (a-Si:C:H), silicon-nitrogen (a-Si:N:H), silicon-germanium ( a-Si:Ge:H) and silicontin (a-Si:Sn:H) alloy systems. Which alloy is chosen depends on the desired band gap (which governs the wave length for 

generating charge carriers), among other things. For example, large band-gap materials serve as a front window in p-i-n 

junctions that prevents absorption of UV light while a low band-gap material permits absorption of red- and infra-red light in 

multilayer (2 to 3-stacked) p-i-n junctions. 
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3.4. Emerging PFC-using fabrication technologies 

Recently researchers have expressed the need to move away from current practices of lowthroughput batch, wet processing towards automated in-line, high-throughput, dry processing for 

PV fabrication using x-Si (Wohlgemuth et al., 2003; Bosch et al., 2004; Shah et al. 2004). Dry 

processing is a generic term indicating little or no use of water during cell fabrication and usually 

refers to plasma technologies for etching and film deposition (Wohlgemuth et al., 2003; Shah et 

al., 2004, Agostinelli et al., 2004; Agostinelli et al., 2005; Rentsch et al., 2005a; Rentsch et al., 

2005b; and Rentsch et al., 2005 c). Dry-processing also entails less physical handling of the xSi wafers, which, as wafers are made thinner to reduce cost and improve efficiency, reduces 

breakage and, therefore, increases yields. 

However, it is important to note that dry processing may not always entail fluorine chemistries 

produced from PFCs or even the use of plasmas. For example in texturing x-Si PVs, reactive 

ion etching (RIE, a plasma etching method) may use either chlorine or SF6/O2 chemistry.11

Researchers seem to emphasize the use of SF6/O2 chemistry, apparently because of the 

hazards of using chlorine (e.g., Cl2 or BCl3). Reports indicate, however, that the only fully dry 

etching process that is in full production is Cl-based RIE chemistry at Kyocera, the second 

largest global manufacturer of PV-cells (Inomata et al., 1997). 

Laser ablation is another method for texturing x-Si under development by researchers, which 

may or may not include plasma technology (Rentsch et al., 2005c, Abbott et al., 2004). 

Texturization is accomplished by stepping and focusing the laser at regular intervals across the 

wafer, ablating Si at each step to the desired depth. While the ablation step has high throughput 

and good yield, the wafer surface must then be cleaned of residual debris (molten and 

recrystallized silicon). The surface may be cleaned via wet chemical- or plasma-etching 

(Rentsch et al., 2005c). For plasma-etching, which the Rentsch et al. preferred to wet-chemical, 

SF6/O2 chemisty was used with microwave plasma. SF6 utilzation rates were not reported 

(Rentsch et al., 2005c). 

When researchers examine fluorine-based plasma chemistry etching, they unanimously 

acknowledge the concomitant emissions of PFCs and point to work of the semiconductor 

industry and the PFC-reduction partnership to identify alternative technologies for abating PFC 

emissions. As was noted at the start of this section, the aim of these researchers is to improve 

the productivity of PV cells fabricated from x-Si, the dominant (roughly 90 percent) solar panel 

fabrication technology. 

Researchers also optimistically express that “it is reasonable to predict that dry processing will 

progressively make its way to production lines as the PV market size grows ... and that, as a 

side effect, this [growth] will contribute to provid[ing] momentum for PV thin-film technologies

(emphasis added), which are largely based on large-area PECVD processes, in that the larger 

market volume for deposition systems will reduce the initial [higher?] investment costs [of the 

PECVD systems].” (Agostinelli et al., 2005). However, the reports identified and reviewed for 

 

11 Chlorine atoms produced in a plasma react with surface atoms of Si to eventually form SiCl3, a gas under process conditions 

that can be pumped away. Similarly, fluorine atoms produced from PFCs react with surface Si atoms to produce SiF4, which is 

also a gas under process conditions (see Flamm, D. L., “Mechanisms of silicon etching in fluorine- and chlorine-containing 

plasmas”, Pure & Appl. Chem., 62 1709 (1990)). See also Kuo, Okajima and Takeichi, “Plasma processing in the fabrication 

of a-Si thin-film transistor arrays”, IBM J. Res. Develop. 43 73 (1999) who also describe the relative virtues of Cl- and PFCchemistries during Si-etching. 
CSBurton 3-6 ICF Consulting

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this report would not support, at least for thin-film technologies, such across-the-board optimism 

for, at least, a-Si PV cells (e.g., BP Solar, 2002; NREL, 2002; Photon International, 2003). 

BP Solar, a global leader in solar cell production, discontinued a-Si and cadmium telluride PVcell fabrication at plants in Virginia and California in 2002. In the summer of 2003, Dunasolar 

Photovoltaics Inc. of Hungary closed its a-Si PV production line which was preceded by 

CalSolar shutting down its California plant in late 2002. 

However, CSG Solar AG, a new German company born out of a joint venture between CSG 

Solar Pty Limited and Pacific Solar Pty Ltd of Australia, is giving new hope to the commercial 

viability of second-generation a-Si thin-film silicon technology. CSG (which stands for crystal 

silicon on glass) Solar uses a single-chamber PECVD system supplied by UNAXIS12 to deposit 

SiNx- and a-Si-alloy-films onto textured glass. The a-Si is converted to its crystalline state by 

high-temperature annealing. A remote plasma system, which generates H-atoms, is then used 

to hydrogenate the crystalline silicon, which removes numerous defects in silicon. The result, 

according to CSG Solar publications, provides commercial-quantity panels with an efficiency 

that exceeds 8 percent (Keevers et al., 2005; Bascore, 2004). CSG Solar does not describe its 

method of cleaning the single PECVD chamber. In January 2005, CSG Solar AG raised 24 

million euros to finance construction and launch its first production facility designed with an 

annual output of 25 MWp (approximately = 312,500 m2

 assuming an efficiency of 8 percent, or 

67 percent of the annual production capacity of one average generation 5 TFT-LCD panel 

manufacturing plant of which there are approximately 13 plants globally in production in 2005, 

(Burton, 2005)). Initial PV-panel production is expected in 2006 (CSG Solar AG, 2005). 

3.5. Potential PFC emissions from existing and emerging 

PFC-using technologies 

Phylipsen and Alsema appear to be the first to report PFC use during PV-panel fabrication 

(Phylipsen and Alsema, 1995). As part of a life-cycle assessment (LCA) of PVs, Alsema et al. 

report a CF4 usage rate of 0.006 – 0.007 kg/m2

 PV-cell area (or 0.01 MTCE/m2) during the 

edge-isolation step (see Section 3.2, step 3). Since no CF4 emissions were reported, it appears 

the authors assumed that all of the CF4 is consumed during cell fabrication, which is not the 

case in semiconductor etch process with CF4. A typical semiconductor etch process during 

semiconductor fabrication utilizes roughly 25 percent of the CF4, with 75 percent vented to the 

atmosphere unless abated. 

Alsema et al. (1997), as part of additional LCA work, reported SF6 use during PECVD chamber 

cleaning after PECVD deposition of a-Si films. A detailed report included an emission factor 

based on a single pilot line from PST in Putzbrunn, Germany (now known as RWE Schott Solar 

of Germany that markets ASI thin-film as well as x-Si solar panels globally) (Nieuwlaar and 

Alsema, 1997). The figure from Nieuwlaar and Alsema is 0.5 g SF6 emitted/Wp of manufactured 

panels, or 12 kg CO2 equivalent/Wp (= 0.5 g SF6 x 23,900 g CO2-equivalent/g SF6/Wp). For a-Si 

PV panels with an efficiency of 0.05 (i.e., a 1 m2

 panel will generate 50 Wp compared to 100 Wp

 

12 UNAXIS is a supplier of PECVD equipment to the flat panel display industry. UNAXIS, however, is currently divesting itself of 

its FPD business (UNAXIS, 2005) and focusing that capability on PV-manufacture. UNAXIS’ PECVD systems are cleaned with 

an in-situ SF6 plasma with a relatively low utilization that leads to large quantities of atmospheric emissions of SF6. Recent 

product descriptions of its KAI-systems for PV-cell production mention use of either SF6 or NF3 for chamber cleaning (see 

Sec. 4.3 of this report). 
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if the efficiency were 0.1), Nieuwlaar and Alsema’s figure becomes 600 kg CO2 equivalent 

emitted/m2

 of panels produced (=12 kg CO2 equivalent/Wp x 50 Wp/m2 of panels produced), 164 

kg CE emitted /m2

 of panels produced (=600 x 12/44), 0.164 MTCE/m2 of panels produced or 

0.000164 MMTCE/m2

 of panels produced. 

As noted in the previous section, recent reports describe the benefits of dry-process (plasma) 

technologies for manufacturing x-Si solar panels (Agostinelli et al, 2004; Rentsch et al., 2005a, 

b; Shah et al,. 2004). Some of the reports provide PFC emission factors, albeit in somewhat 

unfamiliar units. 

Agostinelli et al. (2004) consider PFC-plasma dry- etching and texturing processes for x-Si solar 

cells. They assume only SF6 usage and provide a factor of 11.9 MMTCO2 emitted/GWp of peak 

power production. In a footnote, the authors indicate that emissions would be 40 – 80 percent of 

this factor, suggesting that 11.9 MTCO2/GWp is the PFC gas usage, not emissions. Taking the 

high end of this range for SF6 emissions, gives an estimate of 9.52 MMTCO2 emitted/GWp, or 

0.338 MTCE/m2

, where an average efficiency of 13 percent (130 Wp/m2) has been assumed (= 

9.52 MMTCO2/GWp x 10-9 GWp/Wp x 130 Wp/m2

 x [12/44] x 106 MTCE/MMTCE). 

Rentsch et al. (2005a) describe the benefits of plasma technologies in three process steps 

during x-Si manufacture: texturing, dry-edge isolation and PSG etch. Sulfur hexafluoride is used 

in the texturing and dry-edge isolation steps, with oxygen included in the former. 

Perfluoromethane (with hydrogen) is used in the PSG etch step because the carbon provides 

the needed selectivity between PSG and Si (see also Rentsch et al., 2005b). The authors 

provide an estimate of the aggregate PFC emissions rate (both SF6 and CF4) for the three 

steps, assuming 80 percent utilization for each step. The figure, extracted from Fig. 7, is 4.6 g 

CO2E of emissions/kWh of electricity generated. Using the authors’ assumption of 850 kWh/Wp, 

the aggregate emission rate can be restated as 3.9 kg CO2/Wp, or 1.07 kgCE/Wp. Further, using 

the authors’ assumption of 15 percent cell efficiency, that aggregate emission rate becomes 161 

kgCE/m2

, which includes the influence of PFC abatement. Using the authors’ unsupported and 

questionable assumption that SF6 and CF4 abatement systems can achieve 98 and 95 percent 

destruction efficiencies, and using their graph to factor the aggregate process emissions rate 

into its SF6 and CF4 components, the abated emissions factor (161 kgCE/m2

) becomes 7.48 

MTCE/m2

 (an average abatement efficiency of 97.5 percent). 

A recent comprehensive survey of European and U. S. PV manufacturers by Fthankis, Alsema 

and Agostinelli (2005) found that 40 – 50 percent of PV manufacturers use relatively small 

quantities of PFCs during etching crystalline silicon wafers and C2F6 during chamber cleaning 

after deposition of SiNx films.13 Their survey revealed no SF6 usage by European or U. S. PV 

manufacturers. Survey results showed that for 2004, 30 MT CF4 usage for European and U. S. 

manufacturers and that CF4 accounted for 99 percent of all PFC usage in 2004, with C2F6

accounting for the remaining one percent. Fthenakis et al. (2005) report that no SF6 usage by 

European or U. S. manufacturers. Fthenakis et al (2005) also provide an aggregate emission 

factor of 0.008 MTCE/m2

 of substrate (which includes CF4 and C2F6 usage and can be 

disaggregated into CF4- and C2F6-specific factors using the mass distribution and global 

warming potentials from the IPCC Second Assessment Report). 

 

13 Fthenakis, Alsema and Agostinelli did not have information from Japanese manufacturers in their survey. As will be shown in 

Section 4 of this report (see Fig. 3), Japanese manufacturers accounted for approximately 50 percent of global PV production 

in 2004 compared to 40 percent for Europe and Japan. 
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Table 1 summarizes PFC usage during PV manufacturing as identified through this research. It 

is immediately evident from Table 1 that PFC use is limited to Si-based technologies, 

specifically etching and, in some instances, chamber cleaning processes.. Solar cells made 

from silicon accounts for more than 90 percent of 2004 production, however, furthermore, 

evidence was found for only SF6-, CF4- and C2F6-use. Although not depicted in Table 1, the 

recent survey of Fthenakis et al. suggests the CF4 dominated PFC-usage in 2004. As previously 

noted, by excluding Japanese production, the Fthenakis et al. (2005) survey included only 40 

percent of the world’s production capacity. Readers are cautioned not to assume that Fthenakis’ 

et al. survey results are representative of those in Japan. As described in section 3.4, Japanese 

manufacturers may be using Cl-based etchants rather than F-based etchants. 

That PFC-use (i.e., F-containing etchants) is associated with PV cells fabricated from Si stems 

from the chemistry of Si and fluorine. Si material can be removed via its reaction with F-atoms to 

form gaseous SiF4, which is pumped away. Importantly and not unexpectedly, PFC-use was not 

a process gas used in fabrication of CdTe and CIGS thin-film PV panels. Fluorine does not react 

with these materials. CdTe and CIGS panels, over the long-term, are considered strong (if not 

favored) competitors of a-Si thin-film technology because they provide intrinsically higher 

efficiencies than a-Si solar systems (5 percent vs. 11-14 percent for solar modules) (Wilcox et 

al., 2004). Despite the attractiveness of thin-film technologies (principally because of the lower 

material cost and the still-unrealized potential for producing large mass-connected collections of 

panels) they account for just 10 percent of global production capacity without any strong trend 

that this share is growing (Maycock, 2005). 

Table 1 also summarizes the reported emission factors, for the processes indicated, as 

identified from this research. For purposes of completeness and convenience to the reader, 

emission factors associated with emerging PV fabrication technologies are included. However, 

because both the emission factors and technologies are speculative, they will not be discussed 

further. Instead, attention is given to the “In-production” category at the top of Table 1. For this 

category, the disparateness of the emission factors is striking: two orders of magnitude, with the 

lower factors corresponding to the recent survey of Fthenakis et al. (2005) and the larger factors 

from the earlier work (vintage 1995-1997) of Alsema and colleagues. Because the work 

reported by Alsema and colleagues considered but a few European manufacturers that included 

data from pilot production rather than full production it is considered less relevant to PFC-usage 

in today’s PV production. Thus, only the emission factors from the survey of Fthenakis et al. 

(2005) will be considered when estimating global emissions. 
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Table 1. Reported status of PFC-use during fabrication of some PV cells 

PV-cell fabrication 

technology 

Process step Gas Emission rate, 

MTCE/m2 Source 

In-production 

x-Si Edge isolation CF4 0.01a Phylipsen and Alsema, 

1995 

x-Si Etching CF4 0.007 Fthanakis et al (2005) 

x-Si SiNx deposition, 

chamber cleaning C2F6 0.001 Fthanakis et al. (2005) 

 a-Si SiNx deposition, 

chamber cleaning SF6 

0.164 Alsema et al., 1997 

a-Si a-Si alloy deposition, 

chamber cleaning ? NA NA 

Limited/prospective 

production

 

x-Si Texturing SF6 0.338 Agostinelli et al. 2004 

 “ Saw damage removal SF6 5.4 Rentsch et al. 2005 

 “ Edge isolation SF6 1.4 Rentsch et al. 2005 

 “ PSG etch CF4 0.7 Rentsch et al. 2005 

a-Si a:Si alloy deposition, 

chamber cleaning 

SF6 NA Shah et al., 2004 

a-Si to x-Si film a-Si alloy deposition, 

chamber cleaning 

SF6? NA Keevers et al., 2005 

Bascore, 2004 

a Represents a chemical usage rate. As noted in the text, the authors appear to assume that all of the SF6

is utilized, which is unlikely. A rough estimate of an emission rate is 75 percent of this value, or 0.008 

MTCE/m2

, which is based on an analogy between SF6 etch rates during semiconductor device 

fabrication. 
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4. Global PV Industry: Installed Capacity, 

Growth, Regional Shares of Production 

Capacity, PFC Emissions and Equipment 

Suppliers 

The PV industry and its advocates seek a significant place in the world’s portfolio of long-term 

sources of energy. That the industry can deliver and is delivering clean, reliable, on-demand 

power in current worldwide markets is undeniable. For some time it has been a “power choice” 

for those in remote areas. Contemporary circumstances position PV-production, therefore, for 

double-digit growth with the concomitant potential for increasing atmospheric releases of highGWP gases used during PV-manufacture. 

4.1. PV production growth 

PV production can point to two decades of 20-plus percent compound average growth rates in 

PV power shipments, exceeding 30 

percent per year since 1996. Cumulative 

installed PV power grew at a compound 

average growth rate of 30 percent over the 

period 1992 to 2003 (IEA, 2004). Further, 

since 1996 actual shipments have 

exceeded forecasts by an average of 6 

percent. A recent global forecast projects 

shipments will reach 4,000 MWp in 2010, 

up 4.2-fold over actual shipments in 2004 

(Maycock, 2005). This forecast is shown in 

Figure 1.14 

At the end of 2003, approximately 1800 

MW of PV power was installed globally 

(IEA, 2004)15. Over 85 percent of this 

capacity is installed in three countries: 

Japan (859.6 MW), Germany (410.3 MW) and the U. S. (275.2 MW) (IEA, 2004). Six countries 

account for another 10 percent of the cumulative installed capacity in 2003 (The Netherlands, 

Australia, Spain, Italy, France and Switzerland, in decreasing rank order) (IEA, 2004). Figure 2 

shows the trends in global shares of cumulative capacity for the top nine countries over the 

period 1992 - 2003. 

 

14 Maycock’s forecast will be used despite recent reports (see footnote 7 of this report) that PV production will be constrained by 

shortages of polysilicon. The projected growth by 2010 can still be achieved provided the additional supply of polysilicon does

return during 2007 and demand for solar power remains, 

15 IEA tracks installed capacity from reporting countries of which the total is 20: Australia, Austria, Canada, Denmark, Finland,

France, Germany, Israel, Italy, Japan, Korea, Mexico, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, United 

Kingdom and USA.. 

Forecast of Global PV Cell Shipments, MWp

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1995

1996

19971998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

20092010

Annual shipment, MWp

Fig. 1 Forecast of global PV-cell production, MWp 
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Of most interest to estimates of PFC use and emissions are trends in regional production 

capacity. Figure 3 presents trends in production (shipped cells, not capacity, which, while 

available, could not be obtained and analyzed within the task resources) for the top regions and 

the rest-of-the-world (ROW) for the 10-year period 1995 – 2004 (Maycock, 2005). Over this 

period, global production increased fifteen-fold. Interestingly, however, Japan dramatically 

increased her share from approximately 20 to 50 percent, with Europe maintaining a share of 

approximately 25 percent and the US loosing share, from over 40 percent to approximately 10 

percent in 2004. 

Country Shares of Installed Global PV Capacity

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Share of global total, %

NLD

ITA

FRA

ESP

CHE

AUS

USA

JPN

DEU

Trend in Regional PV Production: 1995 2004

0%

20%

40%

60%

80%

100%

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Share of production, % of MWp

ROW

Europe

Japan

U.S.

Fig. 2. Country shares of installed PV capacity 

Fig. 3.Trends in regional PV production: 1995 – 2004. 
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4.2. An initial estimate of uncontrolled, global PFC 

emissions for 2004 and 2010 

Figure 4 shows total production figures expressed in units of panel area shipped for the period 

1996 to 2004 (Maycock, 2005). In converting MWp to panel area, the global average efficiency 

for each year was used, assuming that average is applicable across each region. The global 

average efficiencies were taken from Wilcox et al. (2004). That the growth in panel area over 

the 1995 – 2004 period increased 14-fold rather than the 15-fold increase in MWp (mentioned 

above) is attributable to the 

increase in efficiency of the 

1995 – 2004 period (more 

efficiency means more power 

per m2

 of cell area). 

The results in Figure 4 (for 

example for 2004) together 

with a suitable emissions 

factor may be used to 

estimate the uncontrolled PFC 

emissions provided emissions 

are directly proportional to 

area of panel produced. The 

findings reported in Chapter 3 

support this proportionality, 

and the aggregate emission 

factor provided by Fthenakis 

et al. (2005) (in Chapter 3) will be taken as the best-available emission factor of uncontrolled 

PFC emissions. 

Using the estimate of 0.008 MTCE/m2

 from the survey of Fthenakis et al. (2005), provides a 

means for estimating global PFC emissions from PV-manufacture. This emission factor is, 

however, applicable to PV-cell manufactured via crystaline-Si technology, which accounts for 95 

percent of the 2004 total production (Maycock, 2005). Using the area of production information 

in Figure 4, together with the fraction of production that employs x-Si, gives 0.07 MMTCE (=0.95 

x 9.125 x 106

 m2 x 0.0.008 MTCE/m2 x 10-6 MMTCE/MTCE). 

This global estimate for 2004 of 0.07 MMTCE, however, neglects any contribution to PFC 

emissions from PFC-use a-Si technology, which accounts for 4 percent of total PV production in 

2004 (Maycock, 2005). While, as was mentioned in Section 3.4), no recent evidence was 

identified in this review of PFC-use to remove a-Si films present on the walls of PECVD 

chambers and Fthenakis et al. report that C2F6 is not used by a major user of a-Si technology, 

an estimate is nonetheless developed for purposes of completeness. 

As a starting point for estimating global emissions from the a-Si sector of the PV industry, the 

emission factor for C2F6 provided by Fthenakis et al. for cleaning PECVD-produced films formed 

during crystalline-Si PV-manufacture seems appropriate (see Table 1, where factor is 0.001 

MTCE/m2

). If this emission factor is assumed applicable to chamber cleaning of PECVD-films 

during a-Si PV manufacture, then the corresponding PFC emissions for 2004 is 0.0004 MMTCE 

(=0.04 x 9.125 x 106

 m2 x 0.001 MTCE/m2 x 10-6 MMTCE/MTCE). The emission factor 0.001 

Trend in Regional PV-Cell Production (m2): 1995 - 2004

-

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Area of panels shipped, m2

ROW

Europe

Japan

U.S.

 Fig. 4.Trends in regional PV-cell production, m2,1995 – 2004.
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MTCE/m2

 from Fthenakis et al. may, however, implicitly reflect the proportion of C2F6 usage 

among those crystalline-Si PV manufacturers that use PFCs, which would tend to understate 

the actual emissions factor (per unit area of silicon consumed during PV manufacture that uses 

C2F6). If it is assumed that only one percent of x-Si PV manufacturers use CF4 and C2F6, the 

0.001 figure of Fthenakis et al. should be multiplied by 100, to give an emission factor of 0.1 

MTCE/m2 of x-Si consumed during chamber cleaning. 

This upwardly adjusted figure, however, needs further adjustment to account for the preliminary 

findings of this review that a relatively small fraction of PV manufacturers seem to use a-Si 

technology to clean PECVD-produced Si-films with C2F6. In fact, it should be recalled that no 

reports were found indicating that C2F6 was used in PECVD-chamber cleaning when a-Si 

technology was employed. If, however, it is assumed that as much as 20 percent of 2004 a-Si 

production capacity employed chamber cleaning with C2F6 (which this non-exhaustive review 

could not identify), the upwardly adjusted emission factor Fthenakis et al. would drop to 0.02 

MTCE/m2

. Using this value and the information in Figure 4, an estimate of C2F6 emissions from 

chamber cleaning within the a-Si PV production sector is 0.007 MTCE (=0.04 x 9.125 x 106

 x 

0.02 MTCE/m2

 x 10-6 MMTCE/MTCE), however, it is recognized that this survey is not 

exhaustive. 

An estimate of the global uncontrolled aggregate emissions from PV manufacturing in 2004 is 

0.077 MMTCE (= 0.07 + 0.007 MMTCE), where 90 percent is estimated to originate from the 

use of x-Si technology to manufacture PV cells and 10 percent from the use of a-Si technology.. 

This estimate of global PFC emissions from PV production (for 2004 levels of production) is 

small compared to the corresponding uncontrolled emissions from semiconductor and TFT-FPD 

manufacture. The estimate for PV manufacturing is but 0.5 percent of the corresponding global 

emissions from semiconductor and 5 percent of global emissions from TFT-FPD manufacture 

(Burton, 2005a, b). 

Using these emission factors for x-Si and a-Si PV-manufacturing technologies, an estimate of 

uncontrolled, global emissions for 2010 can be completed. Maycok (2005) forecasts that by 

2010, the global production PV capacity will have grown to 4,000 MWp. Wilcox (2004) projects 

that by 2010, the average efficiency of PV-cells will have increased from 13 in 2004 to 15 

percent (i.e. 150 Wp/m2 of panel area), which represents a weighted average over all x-Si and 

thin-film technologies. Forecasts of PV-production by manufacturing technology (x-Si, thin-film, 

etc) were not publicly available. It can be expected that PV-manufacturers that use thin-film 

technologies will endeavor to increase market share during the period of constrained supply of 

polysilicon. If it is assumed that Maycock’s 2010 forecast will be achieved and that thin-film 

technologies (specifically the a-Si technology) will approximately triple its share of production 

capacity by 2010 at the expense of x-Si technology, the share of a-Si capacity will grow from 4 

to 13 percent with the corresponding share of x-Si capacity dropping to 86 percent (from 95 

percent). The remaining 1 percent of production capacity is assumed to be employing thin-film 

technologies that do not use PFCs (which compared to x-Si and a-Si manufacturing 

technologies are considerably more costly albeit more efficient. Assumptions about technologyspecific improvements in efficiency are also required. Information from Wilcox (2004) suggests 
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that x-Si will increase to 160 MWp/m2

 while the efficiencies of cells made using a-Si will improve 

to 100 MWp/m2

.

16 

These figures together with the previously developed emissions factors, yields 0.3 MMTCE for 

an estimate of the global, aggregate 2010 uncontrolled PFC-emissions during PVmanufacture.17 

This estimate, which may be characterized as business-as-usual amid an industry that wishes 

to be anything but usual, may be compared with the corresponding 2010 figures for 

semiconductor and TFT-LCD manufacturing. The corresponding figures for semiconductor and 

TFT-FPD manufacturing are 28 MMTCE and 8.7 MMTCE, respectively. One can only conclude 

that at current PFC-usage rates, uncontrolled PFC emissions from PV-manufacturing by 2010 

will be small compared to the corresponding estimates for semiconductor and FPD display 

manufacturing. However, it should be noted that both semiconductor and FPD manufacturers 

have committed to achieving 2010 emissions by as much as 90-95 percent below their 

projected uncontrolled emissions, or approximately 2 to 3 MMTCE. Assuming those targets are 

achieved, the uncontrolled, aggregate emissions from PV-manufacture might then become 10 to 

15 percent of the emissions from semiconductor and FPD manufacturing. 

In concluding this section it seems worth mentioning that the PV equipment manufacturers do 

not yet seem to offer production-line dry-processing tools—the tools that would use PFCs and if 

used might emit uncontrolled PFC emissions—at sustainable business levels (e.g., UNAXIS 

recently announced it’s aim to divest itself of its PV-equipment division). If, however, PV-cell 

manufacturers concluded that dry processing could deliver on the promised lower PV-cell 

manufacturing cost and quality, it would take several years to ramp-up equipment production at 

levels to affect cell production. For example, both the semiconductor and LCD fabrication 

industries have coordinated infrastructures and experience in quickly ramping up production 

using new manufacturing processes. Using the ITRS for semiconductors as a guide, it is evident 

that it takes 5-years to go from a decision to use a new technology to putting it into production 

(and that production at that time accounts for approximately 50 percent of maximum production 

for that technology) (ITRS, 2004). 

If this technology development and adoption rate could be achieved in the PV industry, which 

seems doubtful in view of its seemingly fragmented uncoordinated infrastructure, then by 2010 

the incremental, uncontrolled, aggregate PFC emissions associated with the use of this dryprocessing technology could approach and exceed the corresponding projected emissions from 

semiconductor and FPD manufacture if the emissions factors in the lower-half of Table 1 are 

assumed. Such an estimate is not provided because of its highly speculative nature. 

 

16 Note that using these projected estimates of technology-specific PV-module efficiencies, the 2010 weighted average module 

efficiency is 150 MWp/m2 (= 0.86 x 160 MWp/m2 + 0.13 x 100 MWp/m2), the average value forecasted (fortuitously?) given by 

Wilcox (2004) for 2010. 

17 This estimate equals [0.008 MTCE/m2 x((0.86 x 4000 MWp x 106 Wp/MWp)/160 Wp/m2) + 0.02 MTCE/m2 x ((0.13 x 4000 

MWp x 106 Wp/MWp)/100 Wp/m2] x 10-6 MMTCE/MTCE where the figures are taken from the discussion in the previous 

paragraph. 
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4.3. PV-cell equipment manufacturers 

This chapter concludes with the findings of an initial review of equipment manufacturers that 

offer PV-manufacturers plasma-etch (reactive ion etch or dry-etch) systems as well as PECVD 

systems. This review seeks to identify companies that offer equipment to PV-manufacturers that 

employ x-Si and a-Si technologies and to ascertain whether those manufacturers recommend or 

require PFC-use. It should be noted, however, that, like the early history of semiconductor 

manufacturing, the PV supply chain is fragmented. Some PV-manufacturers such as BP Solar, 

Kyocera, Sharp and Energy Photovoltaics (among others) appear to design and manufacture 

most if not all of the required PV-fabrication equipment internally, others, such as the ErSol 

Group and SCHOTT Solar, produce and design manufacturing equipment as well as purchase 

equipment provided by others. 

As described in Chapter 3, while wet-etching is currently the predominant process for etching xSi substrates during PV-manufacture, the increased plant throughput promised by dry-etching 

appears to be attracting interest. As also noted in Chapter 3, however, RIE may be 

accomplished with either F- or Cl-based chemistries for PV-manufacture, with, in the case of Fbased chemistry, the fluorine provided by PFCs (SF6 or CF4, for example). So, one cannot infer 

that increased use of dry-etching technologies during PV-manufacture necessarily results in 

proportional increase in PFC-use. 

PECVD systems, it appears, are already widely used to deposit SiNx (passivation) films in PVmanufacture (using x-Si or a-Si technologies) and to deposit a-Si (and crystalline silicon on 

glass, CGS) thin-films during fabrication of the photodiode. However, PFCs are not used to 

deposit either SiNx or a-Si films. Instead, PFCs may be used to occasionally clean depositionreactor/chamber walls (and other reactor components) of either of the fugitively deposited Sifilms. While cleaning these chambers with PFCs is the standard practice in both semiconductor 

device and FPD manufacture, it has not been, apparently, the case during PV-manufacture. 

Two European equipment manufacturers appear to be leaders in offering PFC-using equipment: 

Roth & Rau, based in Germany, and UNAXIS, based in Switzerland. Roth & Rau equipment 

uses PFCs (specifically SF6 and CF4) in x-Si etching processes to achieve reported throughputs 

of 600 to 800 wafers per hour for PV-cell manufacture (http:www.roth-gau.de/). Roth & Rau also 

offer PECVD equipment, however no information was identified indicating how the chambers 

are cleaned. Roth & Rau appears often at technical conferences but evidence of equipment 

sales was not found. UNAXIS, as a European supplier of thin-film deposition equipment to the 

semiconductor and flat panel display industries, has restructured and repositioned itself to 

service the solar industry, at the same leaving the flat panel display business. UNAXIS provides 

PECVD equipment for depositing a-Si and SiNx films, which uses SF6 and NF3 for in-situ 

cleaning of the deposition chambers. UNAXIS’ equipment (particularly the KAI-1200) is a key 

component of CGS Solar’s novel PV-cells (see Basore, 2003). Recently the ErSol Group and 

SCHOTT GmbH have also placed large equipment orders for UNAXIS’ KAI-1200. (see 

www.unaxis.com). 

BP Solar (the UK) and Kyocera (of Japan) are two of the largest global PV-manufcturers using 

wet etching. BP Solar, while an early leader in the adoption of PECVD SiNx films for improving 

panel efficiency and longevity, published information about reactor cleaning was not found. 

The PV-equipment manufacturing industry in the U. S. appears to have, compared to its 

European-based competitors, a fragmented customer base. GT Solar, based in New 

Hampshire, while offering, among a large array of PV-equipment, wet and dry etch systems and 
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PECVD systems, it does not indicate the use of PFCs. Plasma Etch, based in Nevada, and 

Kurdex Thinfilm Equipment, based in California, while offering dry etch and PECVD equipment 

to the PV-industry, appear to be suppliers to small, specialty manufacturers in the aerospace, 

electronics and semiconductor industries. Energy Photovoltaics, however, while offering 

equipment, seems to provide full-service, turn-key PV-manufacturing facilities that recently 

emphasizes a-Si technology that does not use PFCs. 

Table 2 summarizes the companies identified in this brief review. Table 2 also indicates whether 

the companies specialize in x-Si or a-Si technologies. 
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Table 2. PV-cell equipment manufacturers 

*Any boxes left blank indicate that th

Company Location Website 

Crystalline (x-Si) 

or Amorphous 

(a-Si) Silicon? 

BOC Edwards The United Kingdom http://www.bocedwards-cme.co.uk/ x-Si BP Solar The United Kingdom http://www.bpsolar.co.uk a-Si Centrotherm Germany http://www.centrotherm.de/index.htm x-Si Energy Photovoltaics New Jersey (U.S.) http://www.epv.net/EPVhome.htm a-Si GT Solar Technologies New Hampshire (U.S.) http://www.gtsolar.com/index.php x-Si Kurdex Thin Film Equipment California (U.S.) http://www.kurdex.com/index.html a-Si Kyocera Japan http://www.kyocerasolar.com/ Unknown OTB Solar The Netherlands http://www.otb-solar.com/index.html a-Si Plasma Etch Nevada (U.S.) http://www.plasmaetch.com/index.html x-Si Roth & Rau Germany http://www.roth-rau.de/ x-Si UNAXIS Switzerland http://www.unaxis.com a-Si 
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5. PFC Emission Control Technologies 

In the course of preparing this scoping report many studies were identified concerning the 

environmental impacts of PV-cell fabrication. The industry appears concerned that, in relying on 

its “clean” image to advance PV technology (no CO2 emissions during the generation of 

electricity and just 2-years of equivalent CO2 emissions during PV-cell manufacture), it is 

obligated to minimize the environmental impact during PV-cell fabrication. Some authors 

mention the use or potential use of PFC emissions, while others are silent on their use. 

The seminal work of Phylipsen and Alsema is an interesting example. As discussed in Chapter 

3, these authors present SF6-usage rates, but they tacitly appear to assume that all of the SF6 is 

consumed—none is emitted. In more recent work, Alsema et al., who seem to track and to rank 

carefully the environmental impacts of alternative PV-manufacturing technologies for the 

industry, fail to even mention a potential PFC use in their recent reports. Fthenakis, who also 

publishes frequently on the health, environmental and safety concerns of PV-manufacturing also 

fails to mention PFC use. A recent comprehensive study of the environmental impacts of PVfabrication, sponsored by EPRI and California Energy Commission, also fails to make mention 

of PFC use (EPRI, 2003). 

Still others bring to the front and center PFC-use during PV fabrication as well as available 

technologies for reducing those emissions. The work of Agostinelli et al. (2004, 2005) and 

Rentsch et al. (2005a, 2005b) are examples. These authors, as previously mentioned in 

Chapter 3, rely heavily on published work by the PFC Reduction/Climate Partnership for the 

Semiconductor Industry. It seems, however, these authors may not fully appreciate that, 

because of the high flows that might be associated with PV-cell fabrication, the abatement 

technologies available to semiconductor manufacturing may not directly apply to PV-cell 

fabrication. Of importance here is the assumption by Agostinelli et al. and Rentsch et al. that the 

DREs reported by the PFC Reduction/Climate Partnership and its vendors are directly 

applicable to PV-cell fabrication. Nevertheless, these authors conclude that both plasma and 

combustion abatement are applicable. 
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6. References 

Abbott et al (2004). M. Abbott, I. Mai and J. Cotter, “Laser Texturing of Multicrytsalline Silicon 

Solar Cells”, presented at 14th International Photovoltaic Science and Engineering 

Conference, Bangkok, Thailand, 2004. 

Agostinelli et al (2004). G. Agostinelli, H. F, W. Dekkers, S. De Wolf, G. Beaucarne, ”Dry 

Etching and Texturing Processes for Crystalline silicon Solar Cells: Sustainability for Mass 

Productions”, presented at 19th European Union Photovoltaic Solar Energy Conference, 

Paris, 2004. 

Agostinelli et al (2005). G. Agostinelli, P.Choulat, H. F, W, Dekkers, S. De Wolf and G, 

Beaucame. “Advanced Dry Processes for Cystalline Silicon Solar Cells”, presented at 31st IEEE 

Photovoltaic Solar Conference, Orlando, Florida, January 3 – 7, 2005. 

Alsema et al. (1997). E. A. Alsema, A. E. Bauman, P. Hill and M. H. Patterson, “Health, Saftey 

and Environmental Issues for Thin-film Manufacturing”, 14th European Photovoltaic Solar 

Energy Conference, Barcelona, Spain, 1997. 

Applied Films (2005). “Applied Films Sells First Sputtering System for Solar Cell Production”, 

February 10. 2005. available at www.appliedfilms.com.de. 

Bosch et al (2004). R. C. M Bosch, W. T. W. Stals, A. J. M. C. Van Erven, R. L. J. R. Pennings 

and M. D. Bijker, “High-throughput PECVD Production Tool for In-line Silicon-nitride Deposition 

on Silicon Solar Cells”, presented at 19th European Photovoltaic Solar Energy Conference, 

Paris, France (2004). 

Basore (2004). Basore, P. A. ”Simplified Processing and Improved Efficiency of Cyrstalline 

Silicon on Glass Modules”, presented at 19th European Photovoltaic Solar Energy 

Conference, Paris, France (2004). 

BP Solar (2002). See Reuters, ”BP Solar drops thin film solar cells, up to 260 US jobs”, 

November, 27, 2002. 

Burton (2005a). “PFC Emissions Vintage Model for Flat Panel Manufacture: Projected 

Uncontrolled and Controlled Emissions 1995-2010”, prepared under Task Order 041, 

Subcontract 22DJ00074, December 20, 2005. 

Burton (2005b). “PEVM Update”, completed under Task Order 041, Subcontract 22DJ00074, 

October 10, 2005 

EPV (2005). Energy Photovoltaics, Inc. See www.epv.net/products/products.htm 

EPRI (2003). ”Potential Helath and Environmental Impacts Associated with the Manufacture and 

Use of Photovoltaic Cells”, Technical Report published by Electric Power Research Institute and 

California Energy Commission as part of Public Interest Energy Research Program (PIER), 

November, 2003. 

Fthenakis, Alsema and Agostinelli (2006). Private communication to Scott Bartos, US EPA, 

February 2005. 

IEA (2004). See www.oja-services-nl/iea-pvps/isr/index.htm 

ITRS (2004). International Technology Roadmap for Semiconductors ... 
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Inomata et al (2004). Y. Inomata, K. Fukui, K. Shirasawa, « Texturizing silicon surface using 

Chlorine”, Solar Energy Materials and Solar Cells, (48), p. 237, 1997. 

Janz et al (2004). S. Janz, S. Bau, F. Lutz, C. Schetter and S. Reber, „PECVD-SI as 

Intermediate Layer for Cystalline Silicon Thin-Film solar Cells on Ceramic Substrates“, 

presented at 19th European Photovoltaic Solar Energy Conference, Paris, France, June 7 – 

11, 2004. 

Keevers et al. (2005). Keevers, M. J., A. Turner, U. Schubert, P. A Basore and M. A. Green, 

“Remarkably Effective Hydrogentation of Crystalline Silicon on Glass”, Proceedings of 20th

European Solar Energy Conference Barcelona, Spain (2005) 

Kenanoglu et al. (2004). A. Kenanoglu, D. Borchert, M. Rinio, M. Abusnina, and S. Diez, 

“Deposition of a-SiNx:H solar Cells at 13.56 MHz”, presented at the 19th European 

Photovoltaic Solar Energy Conference, Paris, France, June 7 – 11, 2004. 

Kumar et al. (2005). B. Kumar, T. K. Pandia, E. Streekiran, S. Narayanan, “Benefit of DualLayer Silicon Nitride Anti-reflectin Coating”, presented at 31st IEEE Photovoltaic Solar 

Conference, Orlando, Florida, January 2005. 

Landsberg (2002). P. T. Landsberg, “Theoretical Limits of Photovoltaic Solar Energy 

Production”, presented at World Climate & Energy Event, Rio de Janeiro, Brazil, January 6-

11, 2002, 

Liehr (2001). M. Lier, “Keeping Pace with the photovoltaic market: Applied Films delivers the firt 

microwave PECVD system to Japan”, available at www.appliedfilm.com.de 

Lossen et al (2005). J. Lossen, L. Mittelstadt, S. Dauwe, K. Lauer and C. Beneking, “Making 

Use of Silicdon Wafers with Low Lifetimes by Adequate POCl3 Diffusion”, presented at 20th

European Photovoltaic Solar Energy Conference, Paris, France, June 7 – 11, 2004. 

Maycock (2005). Paul D. Maycock, “PV Market Update:2004”, PV News, Vol 23, No. 3, March 

2004. Information purchased via www.pvenergy.com 

Nanosolar (2005). See www.nanosolar.com for descriptions of its roll-on and painting processes 

for PV cell manufacture. 

Nieulwaar and Alsema (1997). E. Nieulwaar and E. A. Alsema, “Environmental Aspects of PV 

Power Systems, report on the IEA PV Task 1 Workshop, Utretch, The Netherlands, pp 25-27, 

June 1997. 

NREL (2002). ”Nationial Center for Photovoltaic Statement on BP Solar Announcement”, 

National Renewable Energy Laboratory, Golden, Colorado, November 27., 2002. 

Pacific Solar (2005) See www.pacificsolar.com

Phylipsen and Alsema, (1995). “Environmental life-cycle assessment of multicyrstalline silicon 

solar cell modules” report prepared for Netherlands Agency for Energy and the Environment, 

Report No. 95057. September, 1995. 

Pichel and Yan (2006). J. W. Pichel and M. Yang, “2005 Solar Year-end Review and 2006 Solar 

Industry Forecast”, Piper Jaffray, January 11, 2006. See also “Polysilicon Shortage Becoming 

Critical?”, Electronic News, July 11, 2005. 
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Photon International (2003).; “Putting on a brave thin-film face”, Photon International: The 

Photovoltaic Magazine, August, 2003. 

Rentsch et al (2005a). J. Rentsch, J. Jaus, Kristin Roth and Raif Preu, “Economical And 

Ecological Aspets of Plasma Processing for Industrial Cell Fabrication”, presented at 

Proceedings of 20th European Solar Energy Conference Barcelona, Spain June 6-10, 2005. 

Rentsch et al (2005b). J. Rentsch, C. Schetter, H. Schlemm, K. Roth and R. Preu, 

“Industrialization of Dry Phosophorous Glass Etching and Edge Isolation for Crystalline Silicon 

Solar Cells”, presented at 20th European Solar Energy Conference Barcelona, Spain June 6-

10, 2005. 

Rentsch et al (2005c). J. Rentsch, F, Bamberg, E.l Schniederlochner and R. Preu., „Texturing of 

Multicrystalline Silicon by Laser Ablation“, presented at 20th European Solar Energy 

Conference Barcelona, Spain June 6-10, 2005. 

Roca and Carabe (2003). F. Roca and J. Carabe, “New R&D Trends in Europe on Thin-Silicon 

Photovoltaics”, presented at 18th European Solar Energy Conference, (2003). 

Shah et al (2004). A. Shah, J. Meir, a. Buechel, U, Kroll, J. Steinhauser, F. Meillaud and H. 

Schade, „Towards Very Low-Cost Mass Production of Thin-film silicon Photovoltaic (PV) Solar 

Modules on Glass” presented at ICCG5 Conference in Saarkbrucker, Germany. July, 2004. 

Soppe et al (2004). W. J. Sopper, B. G. Duijvelaar, S. E. A Schiermeir, A. W. Weebar, A. 

Steiner and F. M. Schuurmans, “A High Throughput PECVD Reactor for Deposition of 

Passivating SiN Layers”, presented at 19th European Photovoltaic Solar Energy Conference, 

Paris, France, June 7 – 11, 2004 

United Solar Systems (2004) “Amorphouse Silicon (a-Si) Solar Technology” from United Solar 

Ovonic Corp. (2004). See www.uni-solar.com.. 

Wholgemuth et al (2003). J. Wohlgemuth, M. Narayanan, R. Clark, T. Koval, s. Roncin, M. 

Bennett, D. Dunningham, D. Amin and J. Creager, Large-scale PV Module Manufacturing using 

Ultra-thin Polycyrstalline Silicon Solar Cells”, presented at WCPEC-3, Osaka, Japan, May 2003. 

Wilcox et al (2004). A. Baumann, Y. Bhargava, Z. X. Liu, G. Nemet and J. Wilcox, “Photovoltaic 

Technology Review”’ available at http://ist-socrates.berkeley.edu/~kammen/C226/BerkeleyC226-PVTechComp.pdf 

Winderbaum et al (2003). S. Winderbaum, A. J. Leo, S. P. Shea, T. D., Koval and B. Kumar, 

“Characterization jof Industrial-scale Remote PECVD SiN Depositions”, presented at WCPEC-3,

Osaka, Japan, May 2003. 

Wolke et al (2005). W. Wolke, J. Catoi, G. Emanuel, J. Liu, M. Ruske and R. Preu, “Surface 

Passivation for Solar Cells by Large Scale Inline Sputtering of Silicon Nitride”, presented at 

Proceedings of 20th European Solar Energy Conference Barcelona, Spain June 6-10, 2005. 
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