CIGS Solar Cells: How and Why is their Cost Falling?

MT5009 ANALYZING HI-TECHNOLOGY OPPORTUNITIES

CIGS Solar Cells

Zhang Xuan (a0068215)Rajendiran Aravind Raj (a0065709)

Wu Yiming (a0068957)

21/04/2011

Outline

Motivation

Solar energy is the most abundant energy and free of cost

MotivationHuman

energy

consumption in

1 year

: 1.11

x 1014 KWh

Solar

energy

supply in 1 hour

: 1.78 x101

4 KWh• Solar energy is a safer, environmental friendly resource to solve energy

crisis, and environmental problems• Solar cell is a commercially available and reliable technology with a

significant potential for long-term growth in nearly all world regions

• Solar cell is projected to provide 5% of global electricity consumption in 2030, rising to 11% in 2050

Motivation

Silicon material price decreased

Source: IEA solar PV roadmap

Outline

Crystalline silicon (c-Si) 85-90% market share

• Cells are typically made using a crystalline silicon wafer (ingots can be

monocrystalline or multicrystalline)

Basic Operation• Silicon crystals are laminated into n-type and p-type layers, stacked on top of each

other. Light striking the crystals induces the “photovoltaic effect,” which generates

electricity

Technology Paradigm of Solar Cells

Methods to improve• New silicon materials and processing• Cell contacts, emitter and passivation• Improve device structure and develop new device

with novel concept• Wafer equivalent technologies• Productivity and cost optimization

Limitation for paradigm• The theoretical limit for a crystalline silicon solar cell is ~ 29%.• The thickness of silicon wafer is hard to reduce

Thin films 10-15% market share

Made by depositing one or more thin layers (thin film) of photovoltaic materials on a substrate. Photovoltaic material convert sun energy to electricity.

Technology Paradigm of Solar Cells

Limitation of paradigm• Light trapping efficiency

• Band gap & grain size

• Low-lifetime of thin film, sensitive to moisture

• Thermo-physical properties of layers and substrates

Methods to improve• Improve quality of substrates and transparent conductive oxides• Cell structure improvement• High rate deposition in large area• Defects and nanostructure improvement

a-Si and uc-Si CdTe CIS or CIGS Dye-sensitized solar cell

Concentrating PVCPV systems use optics to concentrate a large amount of sunlight onto a

small area of solar photovoltaic materials to generate electricity.

High cost with super high efficiency (can reach 50%)

Technology Paradigm of Solar Cells

Methods to improve• Semiconductor properties• Solar tracking system• Optic concentration

Novel technologiesDevelop active layers which best match the solar spectrum or which modify the incoming solar

spectrum. Both approaches build on progress in nanotechnology and nano-materials.

Structures of the active layer - quantum wells, quantum wires and quantum dots.

Key issues - collection of excited charge carriers (hot carrier cells) and the formation of intermediate band gaps.

Ultra-high efficiency with full spectrum utilization

Methods to improve• Characterization and modeling of especially nano-structured materials and devices • Processing

Different PV technologies market share

Different PV technologies market share

CIGS Technology: •Copper indium gallium (di)selenide (CuInxGa(1-x)Se2)

•I-III-VI2 compound semiconductor material 

CIGS Thin Film Solar Cell

• Direct band gap material• Multicrystalline nature • Band gap can be varied from 1.0 eV to 1.7 eV • Light absorber (Active Layer) material for TFSC

Outline

•Short energy pay back time and less energy consuming process(1/3 of silicon)•Adaptability - transferable know how from existing industry• LCD industry technology

•Lightweight and light bulk, Can be manufactured on flexible substrate• lead to niche market applications. E.g. BIPV

•Less environmental footprint for recycling for CIGS• Green technology compared with silicon solar cell

CIGS Value Proposition Performance• Highest energy conversion efficiency among all thin-film solar

cells (≈ 19% in small area cells, ≈ 13% in large area modules)• Highest light absorbance (105 /cm) of all thin films• No intrinsic degradation, excellent durability especially

outdoor especially strong sunlight and high temperature (30 years)

Cost advantage• Simple module structure/manufacturing process and cheap

installation• Less raw material utilization fabricated on cheap substrate• Integrated manufacturing: from raw materials to end

products• Higher efficiency reduces area of PV modules

CIGS –Working Principle

P Type

N Type

Light shining on the solar cell produces both a current and a voltage to generate electric power.

Generation of light-generated carriers

Collection of the light-generated carriers to generate a electric current

Generation of a large voltage across the solar cell

Dissipation of power in the loadCIGS Solar cell

By adjusting ratio of CIGS mixture , the broad energy band distribution can be achieved. CIGS absorb light of different wavelengths in solar spectrum. It has wide solar spectrum response and is capable of fully utilizing incident light compared to it competitors .

% I can absorb more light than other thin films – CIGS %

Courtesy : AUO Solar

Why CIGS has high efficiency than other thin films?

Outline

Does the CIGS has reached maximum efficiency ?

CIGS absorber layer quantum efficiency might have reached saturation, but improvements can be done in cell structure and materials used for fabrication to increase efficiency. End user is concerned about cost also.

Improvements in components

• Buffer layer CdS can be modified using ZnS, InS, ZnSe etc (Voc,Isc)• An anti reflective layer is used to reduce front surface reflection loss( Pin)• Contacts can be made thinner /transparent to allow more sunlight to reach

the cell and low resistivity materials can be considered. (21 % without contacts)

CIGSSe Technology Tandem Cell Structure

Source : Univ. of Johannesburg Source : NREL

Improvements in components

Improvements in modules CIGS

Substrate Cell

Module

* Laser scribing * Monolithic fabrication * More transparent , less absorption glass for lamination* Ink based printing technology on flexible substrates* BOS improvements

Controversies between research and industrial results !

Improvements in Systems

• Needs duplication of equipments used for research in larger scale• Uniform & quality deposition of thin films over large area • Role of contaminants and some unexplained stories too….

Courtesy: Global Solar

Latest CIGS Update

Industry Research

Efficiency : 20.3 %Area : 0.5 sq.cmsCentre for Solar Energy and Hydrogen Research ZSW

Efficiency : 15.7 %Area : 1 sq.mMiaSolé

Outline

Cost & Efficiency Analysis

Cost: CIGS < c-Si? Manufacturing Steps

Cell Module

Si – Wafer Solar Cell CIGS Solar Cell

Substrate Substrate

Cell Module

The monolithic integration of thin-film PV can lead to significant manufacturing cost reduction compared to c-Si technology.

Cost Comparisons for thin film Solar Panels

Cost Summary (per sq. meter) 20 MW Plant 2 GW Plant Net Gain

Coated Glass $ 23.62 $ 4.62 5 x

Operating Expenses $ 4.00 $ 1.50 2.5 x

Materials and depreciation

a-Si $ 2.33 + $ 13.35 $ 0.31 + $ 2.67 5x

CdTe $ 3.46 + $ 10.00 $ 2.33 + $ 13.35 7.5x

CIGS $ 13.96 + $ 13.35 $ 9.31 + $ 2.67 7.5x

Assembly, Packaging & Interconnect $41.71 $ 10.50 4x

Overall process yield 60 % 93 % 1.55x

Cost: a-Si vs. CIGS & CdTe

a-Si has the lowest manufacturing costs/watt, but its low conversion efficiencies, <10%, require a greater investment in the BOS components, the supporting infrastructure that includes mounting structures, inverters and electrical wiring. 

By contrast, CIGS and CdTe have demonstrated efficiencies approaching and exceeding a-Si.

a-Si

CIGS

CdTe

Cost: CIGS > CdTe

• CIGS and CdTe cells share common characteristics and device structural elements.

• In principle, the cost/area should be similar, thus, efficiency becomes a crucial factor for cost/watt.

• However, production processes in terms of throughput and yield can differ significantly and may offset the advantage of higher performance.

• Its production is not easy as four different materials are used.

• This is the reason why CdTe has low cost advantage over CIGS.

Low Cost Processing of CIGS [1]• Conventional best-performing CIGS deposition processes: • co-evaporation

• by sputtering of the metals, followed by selenization with H2Se.

• These two processes suffer from relatively slow throughput, poor material utilization, and relatively high vacuum.

• One such example is a process that uses nano-components to make printable precursors that are crystallized into CIGS.

• Need for Low-Cost, High-Throughput Processes.• A lower-cost process should feature high deposition rates, high material utilization, and

simpler equipment capable of processing very large substrates.

Used by Global Solar and Wurth Solar

Reference: M. Kaelin, Low cost processing of CIGS thin film solar cells, solar energy, 2004

Non-vacuum absorber formation techniques

Low Cost Processing of CIGS [2]

Pros Cons

Use low cost equipment Lack of a high purity vacuum environment – need careful choice of precursor materials and additives to avoid undesired contamination.Enable fast processing speed

Quality improved, material is annealed at a higher temperature

Often poor quality, includes impurity phases and may be amorphous or microcrystalline due to the low deposition T (<400 °C)

Reference: M. Kaelin, Low cost processing of CIGS thin film solar cells, solar energy, 2004

Low Cost Processing of CIGS [3]

• Chemical spay pyrolysisOne of the best-investigated non-vacuum deposition processes, but few results were

reported.• Pros: Very suited for uniform large area coating.• Cons: Impurity phases, Traces from reaction by-products, Small grain-size obtained.

• Paste coatingTypically includes screen printing, doctor-blade coating and curtain coating.• A fast process can be applied to continuous roll-to-roll deposition.• Very efficient use of material, exhibits high packing densities.• Does not require expensive vacuum equipment, manufacturing cost per square meter is

significantly lower compared to vacuum deposited absorber layers.

Reference: M. Kaelin, Low cost processing of CIGS thin film solar cells, solar energy, 2004

The Electrodeposition Process

• SoloPower has developed a low cost electro-deposition process to manufacture CIGS solar cells and modules

• A conversion efficiency approaching 14% has been confirmed at NREL

• Modules have been manufactured demonstrating process flow

electrolyteanode

VV

Reference: Rommel Noufi, Thin Film CIGS Photovoltaics, SoloPower, Inc.

The Electrodeposition Process

• Hardware is low cost

• Can be high throughput once the hardware is tuned to the specifics of the process

• Near 100% material utilization

• Pre-formed expensive materials are not required, e.g. sputtering targets, nano-particles

• Crystallographically oriented CIGS films with good morphology and density have been demonstrated

• Thickness and composition control of the deposited films are integral part of the process

• Readily scalable

Reference: Rommel Noufi, Thin Film CIGS Photovoltaics, SoloPower, Inc.

ISET’s Ink-based Fabrication of CIGS

• International Solar Electric Technology• Currently developed a novel ink printing method for fabricating CIGS thin-

film solar cells.• Significantly lower manufacturing costs than all current solar cell

technologies.

• Combines the following advantages to achieve low costs• Exceptional utilization of materials• Low capital equipment expenses• Application over various area formats due to versatility printing• Excellent compositional uniformity established within ink formation,

resulting in high production yields• Adaptability to flexible substrates• Efficiency reaching above 14%, with large potential for performance

improvements.• Robust module architecture that reduces assembly costs and minimizes

field service failures.Reference: Competitiveness of Ink-Based Thin-Film Photovoltaics, Advantages of ISET’s Printed CIGS over other Current Photovoltaic Technologies

ISET’s Monolithically Integrated CIGS Modules

Reference: Competitiveness of Ink-Based Thin-Film Photovoltaics, Advantages of ISET’s Printed CIGS over other Current Photovoltaic Technologies

ISET’s Ink-based Fabrication of CIGS

Ink-Based CIGS Production Process Sequence – very simple

bare glass

metalized glass

ink-coated substrate

final CIGS module

Reference: Competitiveness of Ink-Based Thin-Film Photovoltaics, Advantages of ISET’s Printed CIGS over other Current Photovoltaic Technologies

ISET’s Printed CIGS vs. High-Vacuum CIGS

High-Vacuum CIGS ISET’s Printed CIGSSteep capital investment required for deposition chambers.

Active materials in ISET’s ink are precisely supplied, materials utilization greater than 95%.

Scale-up of costly vacuum equipment to large-area format requires correspondingly high capital expenditure.

ISET takes advantage of economical printing technologies that are well established for high-volume production.

Expensive In, Ga are deposited on the walls of the chambers, costly to recycle.

Low capital expense facilitates sequential production volume expansions.

Poor utilization of metals at high-volumes diminishes economy-of-scale benefits.

Extremely low manufacturing costs allow for market-competitiveness at each stage of production capacity development.

High cost of production prevents cost-competitiveness.

Reference: Competitiveness of Ink-Based Thin-Film Photovoltaics, Advantages of ISET’s Printed CIGS over other Current Photovoltaic Technologies

ISET’s Monolithically Integrated CIGS Modules

Reference: Competitiveness of Ink-Based Thin-Film Photovoltaics, Advantages of ISET’s Printed CIGS over other Current Photovoltaic Technologies

Outline

Direct opportunities - applications• Solar power plants (lightweight, light bulk and flexibility

enables to install in more harsh places)• Power supplies for satellites and space vehicles (high

efficiency and radiation hardness)• Decentralized power supply - Building Integrated PV, foldable

or rollable panels (flexible substrate and light bulk)• transparent substrates apply to large areas like windows • thin substrate can be painted onto aircraft wings

• Power supply for portable purposes (lightweight and high efficiency)

• Consumer products such as watches, toys and calculators • Power supply for emergency and remote areas (durability and

high efficiency)• solar powered water pumping & water treatment system• remote lighting system & PV powered electric fencing• telecommunications and remote monitoring Systems• PV powered storage batteries, vehicles and traffic control signal• vaccine and blood storage refrigerators for remote areas

Future opportunities

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CIGS solar cell value chain

opportunities lie in each segment of the chain

Entrepreneurial Opportunities

Material and chemical supplier

For CIGS solar cell manufacturing, process control starts with the material: the target.If process starts with inadequate material, process will yield inadequate results.

• CIGS absorber layer materials - elemental copper, indium, gallium, selenium• Individual components that make up the CIGS layer - inks, nanoparticles• Suspension solvents and additives such as resins and wetting agents• Other materials - transparent conductive oxides (TCOs), molybdenum and zinc oxide used for the contacts• New materials substitutes used in non-vacuum deposition of the electrode layers

Flexible substrate - Cheaper, Flexible and Larger

• Encapsulation Materials – make multiple alternating layers

of polymer and ceramic films• Ultrathin, Flexible Glass and Glass‐like Composites• Polyimide Films – dominated by polymer substrates

Entrepreneurial Opportunities

Material and chemical supplier

For CIGS solar cell manufacturing, process control starts with the material: the target.If process starts with inadequate material, process will yield inadequate results.

• CIGS absorber layer materials - elemental copper, indium, gallium, selenium• Individual components that make up the CIGS layer - inks, nanoparticles• Suspension solvents and additives such as resins and wetting agents• Other materials - transparent conductive oxides (TCOs), molybdenum and zinc oxide used for the contacts• New materials substitutes used in non-vacuum deposition of the electrode layers

Flexible substrate - Cheaper, Flexible and Larger

• Encapsulation Materials – make multiple alternating layers

of polymer and ceramic films• Ultrathin, Flexible Glass and Glass‐like Composites• Polyimide Films – dominated by polymer substrates

Entrepreneurial Opportunities

Entrepreneurial OpportunitiesOpportunities for Solar Panel Firms and Service Firm• Installation and maintenance of solar panels and solar energy

products - hardware engineers, turnkey system integrators and trainers

• Outside firms like roof and building firms come in as BIPV installer

• Training people for the solar energy industry

• Trading of solar panels and a range of solar energy products