Thin film amorphous silicon solar cells have several advantages over crystalline silicon cells, including lower material costs, lighter weight, and the ability to be deposited on flexible substrates. Amorphous silicon is deposited using plasma-enhanced chemical vapor deposition with silane gas. The cells suffer from light-induced degradation over time due to increasing defect densities, but this can be mitigated through hydrogen dilution during deposition or alloying with elements like fluorine or germanium. Large-scale production uses roll-to-roll manufacturing processes to cut costs. Current research aims to improve deposition rates and cell efficiencies.
CIGS solar cells are one of the leading thin film solar cells to be made commercially viable. There are a lot of ways in manufacturing it and we have specialized a two stage process which gives advantages over material growth during commercial manufacture. An advancement of the two stage process is done to increase the throughput and maximize profits. A lab scale emulation of the commercial process is done to study device performance as a result of the advanced process. Factors such as reproducibility and elemental optimization were a concern and the reason behind these concerns were researched. This thesis serves as an experimental test bed to study device performance before up-scaling the growth recipe for pilot production.
introduction,advantage and disadvantage of solar energy,Generation of solar cell: 1st 2nd 3rd generation solar cell , I-V characteristics, working,application, efficiency data and advantage solar cell.
CIGS solar cells are one of the leading thin film solar cells to be made commercially viable. There are a lot of ways in manufacturing it and we have specialized a two stage process which gives advantages over material growth during commercial manufacture. An advancement of the two stage process is done to increase the throughput and maximize profits. A lab scale emulation of the commercial process is done to study device performance as a result of the advanced process. Factors such as reproducibility and elemental optimization were a concern and the reason behind these concerns were researched. This thesis serves as an experimental test bed to study device performance before up-scaling the growth recipe for pilot production.
introduction,advantage and disadvantage of solar energy,Generation of solar cell: 1st 2nd 3rd generation solar cell , I-V characteristics, working,application, efficiency data and advantage solar cell.
This ppt gives you the basic introduction, talks about it's inception, the basic physics behind it and mainly the fabrication process and after that it discusses the uses and future prospects of it.
Q: What is photovoltaics (solar electricity) or "PV"?
A: What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar
electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from
the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta
(1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as
light-electricity. And that's just what photovoltaic materials and devices do; they convert light energy to
electricity, as Edmond Becquerel and others discovered in the 18th Century.
Q: How can we get electricity from the sun?
A: When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they
release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric
effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It
is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to
electricity.
Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy,
corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they
may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate
electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the
PV cell (which is actually a semiconductor).
With its newfound energy, the electron escapes from its normal position in an atom of the
semiconductor material and becomes part of the current in an electrical circuit. By leaving its position,
the electron causes a hole to form. Special electrical properties of the PV cell—a built-in electric
field—provide the voltage needed to drive the current through an external load (such as a light bulb).
Q: What are the components of a photovoltaic (PV) system?
A: A PV system is made up of different components. These include PV modules (groups of PV cells),
which are commonly called PV panels; one or more batteries; a charge regulator or controller for a
stand-alone system; an inverter for a utility-grid-connected system and when alternating current (ac)
rather than direct current (dc) is required; wiring; and mounting hardware or a framework.
Q: How long do photovoltaic (PV) systems last?
A: A PV system that is designed, installed, and maintained well will operate for more than 20 years. The
basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than
30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it
installed and maintained properly. Experience has shown that most problems occur because of poor or
sloppy system installation.
A solar cell is an electrical device that converts the energy of light directly into electricity
The first practical photovoltaic cell was publicly demonstrated on April 25, 1954 at Bell Laboratories.
From 2002 we can see the modern solar cell.
In this work, I am showing a faithful atomistic process of estimating the oxygen migration energetics within BSCF, oxygen migration energy exhibit a strong dependence on different local atomic structures of this doped perovskites. In addition, DFT calculations exhibit the reason of cubic phase stability of this doped perovskite in variable oxygen concentration.
The most common type of solar cells are Photovoltaic Cells (PV cells)
Converts sunlight directly into electricity
Cells are made of a semiconductor material (eg. silicon)
Light strikes the PV cell, and a certain portion is absorbed
The light energy (in the form of photons) knocks electrons loose, allowing them to flow freely, forming a current
Metal contacts on the top and bottom of PV cell draws off the current to use externally as power
This ppt gives you the basic introduction, talks about it's inception, the basic physics behind it and mainly the fabrication process and after that it discusses the uses and future prospects of it.
Q: What is photovoltaics (solar electricity) or "PV"?
A: What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar
electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from
the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta
(1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as
light-electricity. And that's just what photovoltaic materials and devices do; they convert light energy to
electricity, as Edmond Becquerel and others discovered in the 18th Century.
Q: How can we get electricity from the sun?
A: When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they
release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric
effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It
is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to
electricity.
Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy,
corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they
may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate
electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the
PV cell (which is actually a semiconductor).
With its newfound energy, the electron escapes from its normal position in an atom of the
semiconductor material and becomes part of the current in an electrical circuit. By leaving its position,
the electron causes a hole to form. Special electrical properties of the PV cell—a built-in electric
field—provide the voltage needed to drive the current through an external load (such as a light bulb).
Q: What are the components of a photovoltaic (PV) system?
A: A PV system is made up of different components. These include PV modules (groups of PV cells),
which are commonly called PV panels; one or more batteries; a charge regulator or controller for a
stand-alone system; an inverter for a utility-grid-connected system and when alternating current (ac)
rather than direct current (dc) is required; wiring; and mounting hardware or a framework.
Q: How long do photovoltaic (PV) systems last?
A: A PV system that is designed, installed, and maintained well will operate for more than 20 years. The
basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than
30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it
installed and maintained properly. Experience has shown that most problems occur because of poor or
sloppy system installation.
A solar cell is an electrical device that converts the energy of light directly into electricity
The first practical photovoltaic cell was publicly demonstrated on April 25, 1954 at Bell Laboratories.
From 2002 we can see the modern solar cell.
In this work, I am showing a faithful atomistic process of estimating the oxygen migration energetics within BSCF, oxygen migration energy exhibit a strong dependence on different local atomic structures of this doped perovskites. In addition, DFT calculations exhibit the reason of cubic phase stability of this doped perovskite in variable oxygen concentration.
The most common type of solar cells are Photovoltaic Cells (PV cells)
Converts sunlight directly into electricity
Cells are made of a semiconductor material (eg. silicon)
Light strikes the PV cell, and a certain portion is absorbed
The light energy (in the form of photons) knocks electrons loose, allowing them to flow freely, forming a current
Metal contacts on the top and bottom of PV cell draws off the current to use externally as power
Solar Power 2020: India On A National Solar MissionHIMADRI BANERJI
India can now make 700 megawatts of photovoltaic modules each year, according to the plan. The aim would be to make 20,000 megawatts of solar cells annually by 2017 and to establish expertise in solar thermal technologies.
Total costs would be 85,000 and 105,000 crores ($18.5 billion to $22.8 billion) over a 30-year period. To help finance the project, the plan foresees a significant tax on gasoline and diesel — fuels the government currently subsidizes.
Overview of advantages and fabrication of solar cells made from silicon nanowires. IT includes few slides of conventional solar cells and benefits of using silicon nanowire.
Introduction about semiconductors and their integration with nanomaterialAbhay Rajput
1)What is Semiconductor?
2)Use of Semiconductor in different sectors.
3)Manufacturing Process
4)Types
5)Semiconductor Nanomaterial process
6)Properties
Building Integrated Photovoltaic Solar Glazing, Current & Emerging TechnologiesGavin Harper
Presentation at the Low Carbon Research Institute Conference, Cardiff, SWALEC Stadium, 18th November 2014 on Building Integrated Photovoltaics Solar Glazing:Current & Emerging Technologies
Best presentation on Germanium based Photovoltaic cell. Photovoltaic cell is also known as Solar cell.
Germanium-based photovoltaic cells use germanium as the semiconductor material to convert sunlight into electricity. Germanium has a wider spectral sensitivity than silicon, allowing it to absorb a broader range of light wavelengths, including infrared. This enables germanium-based cells to generate electricity more efficiently under various environmental conditions. They exhibit higher conversion efficiencies, particularly in low-light or low-temperature scenarios, thanks to germanium's high carrier mobility. These cells find applications in thermophotovoltaic systems for energy harvesting from waste heat. Germanium-based cells can also be integrated into tandem or multi-junction solar cell structures, increasing overall efficiency by capturing a wider spectrum of light. Ongoing research focuses on improving performance, reducing costs, and enhancing material durability. Challenges include the availability and cost of germanium, but these cells show promise for specialized applications such as space-based solar power systems, portable electronics, and wearable devices. Advancements in crystal growth techniques and material engineering contribute to their progress. By addressing these challenges and furthering research, germanium-based photovoltaic cells have the potential to play a significant role in solar energy conversion.
Dipole-directed self-assembly can be used to create robust one-dimensional nanostructures
on silicon. It also provides new insights into interactions between molecules and this important
technological material.
International Journal of Computational Engineering Research(IJCER) is an intentional online Journal in English monthly publishing journal. This Journal publish original research work that contributes significantly to further the scientific knowledge in engineering and Technology.
A window on the future of solar glazingGavin Harper
This presentation looks at some of the advances in glazing incorporating Solar Photovoltaic devices in order to generate electricity. It looks at a range of technologies including Organic Solar Concentrators, Luminescent Solar Concentrators, Pythagoras Solar's unique glazing system, Dye sensitised solar cells and Honeycomb Thin Film Devices.
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Macroeconomics- Movie Location
This will be used as part of your Personal Professional Portfolio once graded.
Objective:
Prepare a presentation or a paper using research, basic comparative analysis, data organization and application of economic information. You will make an informed assessment of an economic climate outside of the United States to accomplish an entertainment industry objective.
1. The Birnie Group solar class
and website were created with
much-appreciated support
from the NSF CRCD Program
under grants 0203504 and
0509886. Continuing Support
from the McLaren Endowment
is also greatly appreciated! Amorphous Silicon Solar Cells
Slides from Graduate Student Presentation by Robert Ochs
in 2004 ‐ mainly Summarizing the chapter entitled
“Amorphous Silicon‐based Solar Cells” by X. Deng and E. A.
Schiff (2002), in Handbook of Photovoltaic Science and
Engineering, edited by A. Luque and S. Hegedus
Slides on these other topics might also be of interest (most collected during teaching years 2004 and 2005):
http://www.rci.rutgers.edu/~dbirnie/solarclass/BandGapandDopingLecture.pdf Band Gap Engineering of Semiconductor Properties
http://www.rci.rutgers.edu/~dbirnie/solarclass/MultijunctionLecture.pdf Multi‐Junction Solar Device Design
http://www.rci.rutgers.edu/~dbirnie/solarclass/MBEgrowth.pdf Molecular Beam Epitaxy
http://www.rci.rutgers.edu/~dbirnie/solarclass/TransparentConductors.pdf Transparent Conductors for Solar
http://www.rci.rutgers.edu/~dbirnie/solarclass/ARCoatings.pdf Anti‐Reflection Coatings for Solar
http://www.rci.rutgers.edu/~dbirnie/solarclass/OrganicPV.pdf Organic PV
http://www.rci.rutgers.edu/~dbirnie/solarclass/DSSC.pdf Dye Sensitized Solar Cells
http://www.rci.rutgers.edu/~dbirnie/solarclass/MotorPrimerGaTech.pdf Working with Simple DC Motors for Student Solar Projects
http://www.rci.rutgers.edu/~dbirnie/solarclass/2005ProjectResultsindex.htm Examples of Previous Years’ Student Solar Projects
Note: in some cases it may be possible to design custom courses that expand on the above materials (send me email!)
Journal Publications of Some Recent Research: (best viewed through department home index: http://mse.rutgers.edu/dunbar_p_birnie_iii)
Other Birnie Group Research:
Sol-Gel Coating Quality and Defects Analysis (mostly Spin Coating): http://www.coatings.rutgers.edu
Solar Research at Rutgers: Broader Overview http://www.solar.rutgers.edu
Solar and Electric Vehicles System Projects (early stage emphasis) http://www.rave.rutgers.edu
Professor Dunbar P. Birnie, III (dunbar.birnie@rutgers.edu)
Department of Materials Science and Engineering
http://mse.rutgers.edu/faculty/dunbar_p_birnie
2. Thin Film Amorphous Silicon
Thin Film Amorphous Silicon Solar Cells
Solar Cells
14:150:491
Solar Cell Design and Processing
3. Thin Film Amorphous Silicon Solar Cells
Outline
• What is amorphous silicon?
• Atomic structure of a-Si:H
• Light induced degradation Effects
• Deposition methods
• Large-scale manufacturing
• Current state of a-Si
4. Thin Film Amorphous Silicon Solar Cells
Amorphous Silicon
• The term “amorphous” commonly applied
to non-crystalline materials prepared by
deposition from gases.
• Non-crystalline:
– Chemical bonding of atoms nearly unchanged
from crystals
– Small, disorderly variation in the angles
between the bonds eliminates regular lattice
structure
5. Thin Film Amorphous Silicon Solar Cells
Hydrogenated Amorphous
Silicon
• In early studies of amorphous silicon, it was
determined that plasma-deposited amorphous
silicon contained a significant percentage of
hydrogen atoms bonded into the amorphous
silicon structure.
• These atoms were discovered to be essential to the
improvement of the electronic properties of the
material.
• Amorphous silicon is generally known as
“hydrogenated amorphous silicon”, or a-Si:H.
6. Thin Film Amorphous Silicon Solar Cells
Advantages of a-Si:H over c-Si
• Technology is relatively simple and inexpensive
for a-Si:H
• For a given layer thickness, a-Si:H absorbs
much more energy than c-Si (about 2.5 times)
• Much less material required for a-Si:H films,
lighter weight and less expensive
• Can be deposited on a wide range of substrates,
including flexible, curved, and roll-away types
• Overall efficiency of around 10%, still lower
than crystalline silicon but improving
8. Thin Film Amorphous Silicon Solar Cells
Atomic Structure
• Same basic structure shared by crystalline and
amorphous silicon
• For amorphous silicon, several percent of silicon
atoms make covalent bonds with only 3
neighboring silicon atoms, the remaining electron
bonds with a hydrogen atom
• 2 principal configurations for hydrogen:
– Dilute: a particular hydrogen atom is about 1 nm away
from any other hydrogen atom
– Clustered: there are two or more hydrogen atoms in
close proximity
– The density of hydrogen atoms depends on how the
material is made
9. Thin Film Amorphous Silicon Solar Cells
Chemical Bonding Defects
• Affect the electronic properties of the
material
• The D-center, or dangling silicon bond, is
the most influential defect on electronic
properties
• The defect density has been shown to
increase, then stabilize, with increasing
illumination time, or “light soaking”
10. Thin Film Amorphous Silicon Solar Cells
Staebler-Wronski
Effect
• There is a significant decline in the
efficiency of a-Si:H solar cells
during first few hundred hours of
illumination
• A-Si:H modules reach steady-state
after about 1,000 hours of steady
illumination
• Seasonal variations in conversion
efficiency were noticed. For a
specific module studied:
– Up to 20 deg. C., there is an
increase in efficiency with
temperature
– c-Si has the opposite, where
there is a decrease in efficiency
with temperature
From Deng, et al. 2002.
11. Thin Film Amorphous Silicon Solar Cells
Defect Density and the Staebler
Wronski Effect
• Researchers believe that the increase in defect density with
light soaking is the principal cause for the Staebler
Wronski effect
• Defect density is the dangling bond, which occurs when
hydrogen does not bond to the fourth silicon bond
• Since defect density increases with illumination, it is
believed that illumination provides the energy required to
push hydrogen away from the fourth silicon bond, creating
a dangling bond
• Also, since it has been found that the density of hydrogen
in the film is determined by how the film is made, it may
be possible to reduce the Staebler Wronski effect with
manufacturing techniques
12. Thin Film Amorphous Silicon Solar Cells
Staebler Wronski (cont.)
• Performance degrades during illumination because
defect density (dangling bonds) increases, which
will capture electrons created by photons
• Researchers have found ways to reduce the effect
by incorporating fluorine in the gas mixture during
production
• Fluorine bonds tighter to silicon than hydrogen,
and is less mobile in the a-Si network
• Fluorinated a-Si cells show much better stability
under light soaking
• Further research into the deposition process will
further improve the fluorinated a-Si cell
13. Thin Film Amorphous Silicon Solar Cells
Degradation of
power with
illumination time
Increase of
defect
density with
illumination
time
From Deng, et al. 2002.
14. Thin Film Amorphous Silicon Solar Cells
Energy Bands
• Perfect crystals, EG=EC-EV
• Amorphous semiconductors
have exponential distributions
of conduction and valence
bands
• There is no single procedure for
locating the band edges
• The bandgap can be
approximated by analyzing
measurements of the optical
absorption coefficient α(hν)
α(hν)=(A/ hν)(hν-ET)2
From Deng, et al. 2002.
15. Thin Film Amorphous Silicon Solar Cells
Doping a-Si:H
• Doping with phosphorous in c-Si raises the fermi energy
level by adding an extra electron
• In a-Si:H, P atoms bond only to 3 silicon neighbors,
leaving 2 electrons paired in “s” atomic orbitals which do
not participate in bonding. This is a chemically
advantageous
• It was found that occasionally, P can bond in a-Si:H as it
does in c-Si, where four electrons are shared with 4
neighboring Si atoms, but a negatively charged dangling
bond is also created
• Therefore, doping in a-Si:H is inefficient
– Most dopant atoms do not contribute a free electron and
do not raise the fermi energy level
– For each dopant that does contribute an electron, there
is a balancing Si dangling bond to receive it
16. Thin Film Amorphous Silicon Solar Cells
Alloying with Additional
Elements
• Alloying with elements, such as Ge, can be
accomplished during film production
• The resulting alloys have wide ranges of
bandgaps
• This can be very useful for creating
multijunction pin cells, where the narrow
bandgap of a-SiGe allows for increased
absorption of lower energy photons
17. Thin Film Amorphous Silicon Solar Cells
Multijunction Cells
• Cell stacking suited for amorphous cells
– No need for lattice matching, as in c-Si
– Bandgaps can be readily adjusted by alloying
• Multijunction a-Si based cells have higher
solar conversion efficiency than single
junction cells
• Most commercially produced a-Si based
cells are multijunction type
18. Thin Film Amorphous Silicon Solar Cells
Spectrum Splitting
• Top junction has higher bandgap than bottom
junction, top junction absorbs higher energy
photons, and passes by the lower energy photons
for the bottom junction to absorb
• Semiconductors with wide ranges of bandgaps can
be created by alloying
• By stacking any amount of cells by decreasing
bandgap, much of the incoming light can be
absorbed and converted
19. Thin Film Amorphous Silicon Solar Cells
Deposition of Amorphous Silicon
• Silane-based (SiH4 gas) glow discharge
induced by RF voltages, or plasma
enhanced chemical vapor deposition
– 13.56 MHz excitation
– VHF
– Remote MW
• Hot-wire catalytic deposition
20. Thin Film Amorphous Silicon Solar Cells
RF PECVD
1. Silicon containing gas, SiH4 and
H2 flows into a vacuum
chamber
2. RF power applied across two
electrode plates
3. A plasma will occur at a given
RF voltage for a specific range
of gas pressures
4. Plasma excites and decomposes
the gas and generates radicals
and ions
5. Thin hydrogenated silicon films
grow on heated substrates
mounted on the electrodes
From Deng, et al. 2002.
21. Thin Film Amorphous Silicon Solar Cells
• Gas pressure Deposition Conditions
– Higher for preparing microcrystalline films
– Lower for uniform deposition
• RF Power
– Higher power for higher deposition rate
– Above 100 mW/cm2, rapid reactions create silicon polyhydride
powder that contaminates the growing Si film
• Substrate temperature
– Lower T, more H incorporated in the film, increases the bandgap
of a-Si:H
• Below 150 deg. C., makes the powder formation worse
– Higher T, less hydrogen is incorporated and the bandgap is slightly
reduced
• Above 350 deg. C., the quality of the material degrades due to
loss of hydrogen and increasing defect density (dangling
bonds)
• Electrode spacing
– Smaller spacing for uniform deposition
– Larger spacing makes maintaining plasma easier
22. Thin Film Amorphous Silicon Solar Cells
Hydrogen Dilution
• Dilution accomplished by mixing in
hydrogen with the silane gas mixture
• Strong dilution has been found to reduce the
defect density and improve the stability of
the material against light-soaking effects
• If dilution is increased significantly, the thin
silicon films will become microcrystalline
23. Thin Film Amorphous Silicon Solar Cells
VHF Glow Discharge Deposition
• It has been determined that the deposition rate of
a-Si films increases linearly with plasma
excitation frequency
• High quality a-Si films have been created at rates
exceeding 1nm/s without making contaminating
polyhydride powder
• Challenges for large scale production include
adapting the technique to larger electrode sizes
24. Thin Film Amorphous Silicon Solar Cells
Indirect Microwave Deposition
• When microwave plasma is in direct contact
with substrate, the deposited films have
very poor optoelectronic properties
• By exciting a carrier gas such as He or Ar,
the carrier gas then excites the silane gas
• This method shows promise for very high
deposition rate, 50 A/s, in the future
25. Thin Film Amorphous Silicon Solar Cells
Hot-Wire Glow Discharge Deposition
• Silane gas is catalytically excited or decomposed
into radicals/ions by a superheated metal filament
(1800-2000 deg. C.)
• Silicon radicals diffuse inside the chamber and
deposit onto the heated substrate
• It has been found that HWCVD deposited a-Si
films show lower H content and improved light
stability when compared with RF PECVD films
• Challenges
– HW can deposit at a very high rate (150-300 A/s)
– Uniformity of HW films still poorer than RF films
– Filament material needs to be improved to reduce
maintenance time
– HW solar cells perform poorer than RF produced cells
26. Thin Film Amorphous Silicon Solar Cells
Large-Scale Production
• Continuous “roll to roll” manufacturing processes
developed by Energy Conversion Devices, Inc.
• A “roll” of flexible substrate (stainless steel) is
unrolled and fed into the manufacturing process,
and rolled back up at the end
• Four continuous processes:
– Substrate washing
– Sputter deposition of back-reflector
– a-Si semiconductor deposition
– ITO top electrode deposition
• Large roll can be cut into different sizes to meet
application needs
27. Thin Film Amorphous Silicon Solar Cells
Pros/Cons of Roll-to-Roll
• Advantages:
– Product is lightweight and flexible
– Product can be cut to different sizes after manufacture
– High production yield can be maintained
• Disadvantages:
– Labor intensive
– The four steps are currently not integrated into one
machine; each step requires drastically different
working pressures
– Cutting process is labor intensive
28. Thin Film Amorphous Silicon Solar Cells
Current State of a-Si
• a-Si cells have been made with 15.2% initial
efficiency and 13% stable efficiency
• Rapid deposition processes are being refined so
that high rate, high quality can be achieved
• Research into light degradation remedies will
provide for cells with efficiencies comparable with
c-Si cells
• New applications for a-Si cells are being sought
such as building-integrated PV, space power,
consumer electronics, grid integration, and large
scale power generation