Maximum thickness to chord ratio (%)

Note: Always found at 0.3 along chord.

Used to find torque.

Assumed to be halfway along blade length.

c_p = 0.593.

It is the ratio of maximum extractable mechanical work to the total power contained in the wind.

It is achieved when the wind velocity after extraction is 1/3rd of the speed before extraction.

The ratio of the tangential speed at the blade tip to the wind velocity.

λ = v_tip/ω = (l+r)ω/v

Where l is length of blade, r is radius of hub.

Drag - In the direction of flow

Lift - At a right angle to the direction of flow

Multiply by rotor power coefficient c_PR.

Angle of attack varies with rotor radius to maintain optimal value for lift coefficient. 

Called blade twist, and is defined as the angle between local airfoil chord and at 70% rotor radius/blade tip.

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What is this?

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What is this?

1) Strength - To withstand the highest wind speeds that may occur

2) Stiffness - For vibrations and critical deflections

3) Fatigue Life - To guarantee full service life (10 to 20 years).

1) Aerodynamic - Aerodynamic loads with uniform wind speed, and centrifugal forces. Generate time-independent, steady-state loads and non-periodic loads caused by turbulence.

2) Gravitational - Due to weight of blades. Larger the turbine, the bigger the loads.

3) Inertial - Inertial forces due to weight of rotor blades cause periodic and non-steady loads.

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Define a, b, c.

a) Continuous and aligned

b) Discontinuous and aligned

c) Discontinuous and randomly aligned

All fibre-reinforced composites.

1) Assume a chunk of the material with certain mass, i.e. 100grams. Use mass factor to find volume of that chunk:

V_c = V_m + V_f = (m_m/ρ_m) + (m_f/ρ_f)

2) Calculate density of chunk using mass and volume:

ρ_c = (m_c/V_c)

Functional - Materials designed to interact with or respond to their environment.

Structural - Primarily used to carry loads and resist mechanical forces. Also for weight reduction and increased temp. capability

- Method of mechanical energy storage.

- Dual-function motor/generator

- Made of lightweight fiber for greater efficiency (85%-95%)

- Short discharge time

Solid cylinder spins at high speed. Electricity is stored as drive motion, turns into a generator to recharge.

Advantages:

- Compact and lightweight

- High cycle life

- Fast response time

Disadvantages:

- Not economical

- Limited discharge time

- Stored in underground cavern, valves opened at peak times.

- Release through turbine when power is needed, turns into electricity

- 40 to 70% efficiency

Advantages:

- Fast startup

- Long lifetime and low maintenance

- Minimal environmental impact

Disadvantages:

- Low efficiency

- Compressing air requires electricity

- Geological structures needed

Advantages:

- Most effective with high capacity of energy (>1GW)

- Long service life and low maintenance

Minimal environmental impact

Disadvantages:

- Geographical dependence

- High capital cost and running cost

- Soil erosion, land inundation

Advantages:

- Low construction cost

-Applicable for heating and cooling (mainly cooling)

- Short payback period

- Minimal environmental impact

Disadvantages:

- Low capacity

- Geographical dependence

- High maintenance cost

P_G = E_G/t_D

where t_D is discharge time.

Advantages:

- No greenhouse gas emissions

- Not much political dependence

- Long operating time

- Lightweight & Compact

Disadvantages:

- H₂ is highly flammable making storage hard, but can use metal hydrides or ammonia as carriers.

- Expensive to produce H₂

- Platinum catalyst -> high capital cost

- Creep 

- Fatigue

- Thermo-mechanical fatigue (can be low temp or high temp)

In a high temperature environment:

- Oxidation > Spalling/dry oxidation

- Hot corrosion - can occur when moisture is present.

Aluminium is lightweight but has low temperature capability. It can be used in outer shell components and nacelle structures.

Can be used for parts of inlet fans.

Have high strength-to-weight ratio but only mid temperature capabilities.

Used in:

-Fan blades and fan disc

- Compressor stages (low to mid pressure)

Used in bearings and shafts.

Good strength and toughness

Used for high-pressure turbine blades, and combustion chambers. Around exhaust.

Excellent temperature capabilities, resistance to creep, fatigue and oxidation.

Used in fan cases and nacelles due to high strength-to-weight ratio. 

Not for high temperature areas.

γ - Matrix

γ' - Precipitates

'Glide and climb'

Have to move towards precipitates then 'climb' around them.

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Grain boundary sliding - Relative movement of grains along their boundaries. This doesn't involve dislocation motion within grains.

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- Vacuum process, reduces oxide contamination. Improved cleanliness.

- Led to considerable improvements in blade properties

- Controlled cooling (directional solidification) allows for micro-structural control.

- Cooling channels can be cast into the blade -> Force through cooling gas

- Blades heat-treated

- Early blades had chromium and carbon additions to produce chromium carbide. Reduced grain boundary sliding, however these aren't necessary in single crystal blades.

- Al, Ti, Ta and Nb were added in 1980s to improve performance.

- Rhenium and Ruthenium recently been added to improve temperature properties, expensive but working on reducing costs. Can use as alloy coatings, thermal barrier coatings (TBCs). Greatly improve temperature capabilities.

- Forced flow of large volumes of cooling air through them

- Requires the implementation of complicated cooling channels

Done at the casting stage:

- Silica rods implemented into the investment casting mould.

- Nickel alloy is cast around them

- Silica chemically etched away once the blade is cooled

- Blade can be machined and holes drilled from the surface to connect internal cooling passages.

- Can be single pass or multi-pass

1) Convection cooling - from internal blade forced airflows.

2) Impingement cooling - from internal airflows directed towards inside blade surfaces.

3) Film cooling - from cold air flowing across blade surface from cooling holes.

4) Transpiration cooling - from cold air flowing through porous regions (not widely used in gas turbines).

- High melting point (ceramic materials).

-Low thermal conductivity, leads to temperature gradient and safer operating temperature

- Typically 300μm of yttria stabilised zirconia is deposited as the thermal barrier.

- Allows about 100°C decrease under steady state conditions.

- To ensure adherence with the nickel super-alloy substrate, a bond coat is needed.

- Typically 100μm of MCrAlY where M is Co or Ni or a mixture.

2 main TBC Coating Process variants?

1) Plasma Spraying

2) EB-PVD

How does plasma spraying work?

- Powder melted in a plasma torch and ejected against the surface of the component where it cools and solidifies (splats) to form a coating

- Major boundaries run parallel to surface

- Thermal conductivity starts low but increases during service.

- Not applied to moving parts, poor thermo-mechanical fatigue

Electron beam physical vapour deposition.

- Solid zirconia is heated by an electron beam until it vapourises.

- The main boundaries run perpendicular to the component surface

- The thermal conductivity is low and remains so in service

-Coatings are resistant to thermo-mechanical fatigue, considering implementation on moving objects.

[image]

Plasma Sprayed TBCs

- Good phonon conduction through splats.

- Inter-splat boundaries disrupt this due to air gaps and reduced porosity.

- Conductivity increases in service due to sintering at high temps.

EB-PVD

- Single column from surface to interface.

- Plasma bombardment during growth causes defects which disrupt phonon modes.

- Stable at service temps

- Adhesion

- Minimising of thermal expansion mismatch stresses (creep relaxation)

- Oxidation protection (gas through porosity in coatings)

– Typically nickel aluminde modified with chromium or

platinum

– Produced by packing the blades in a pack of aluminium

powder and an activator and heating the pack in a retort

– Aluminium is transported to the surface of the blades

where it diffuses inward, creating the aluminide from the

blade material

- To incorporate Pt in the diffusion layer the blade is coated

with this elements first by electroplating

- The Pt slows down diffusion in the alumina scale and

increases bond coat life

1) Thermo-mechanical fatigue cracking

2) Erosion

3) Fluxing of yttria stabiliser (silica deposits)

4) Bond coat failure (either oxidation or creep)

R=ρL/A

R = Resistance

ρ = Resistivity

L = Length

A = Cross-sectional area

Conductance - Inverse of resistance. Ease that electrical current passes. SI unit is Siemens (1S = 1/Ω)

Conductivity (σ) - Inverse of resistivity, how much a material allows current). σ = 1/ρ

Two probes apply a current and measure the voltage between them. Done to derive resistance. Contact and internal resistance unfortunately added to sample resistance.

Underestimates conductivity, and overestimates resistance.

Four-point probe uses four probes to apply current and measure voltage. Compensates for the effects of contact resistance and internal resistance of the system.

Used for films and coatings

How is sheet resistance calculated?

2 equations and units?

Measure of lateral resistance across a thin, square sheet of metal. Resistance of opposite sides of square. Found using a 4-point probe. Independent of size!

Units: Ω/sq

Equation: R_S = ρ/t, R_S = 4.532V/I

Where ρ is resistivity and t is thickness.

Ratio of maximum charge (Q) that can be stored in a capacitor to the applied voltage (V) across its plates, SI unit is Farad.

C = Q/V, 1F = 1C/1V

Insulators, no current flows through when a voltage is applied but they become polarised.

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The better the dielectric the better the capacitance.

Oxidation: Reaction at electrode in which electrons are generated (something loses electrons)

Reduction: Reaction at electrode in which electrons are consumed (something gains electrons)

Reduction current: Flow of electrons from electrode to solution, negative potential.

Oxidation current: Flow of electrons from solution to electrode, positive potential.

Think of it as the reaction happening in the electrolyte.

Galvanic reactions are spontaneous, meaning positive cell voltage.

Electrolytic reactions are non-spontaneous, meaning negative cell voltage.

Voltametric techniques use potential of an electrode as the controlled variable, current is observed variable. Used potentiostat. 

Galvanostatic techniques have current as controlled variable, voltage is observed. Uses galvanostat.

Working electrode's potential is controlled with respect to reference electrode, whilst measuring current flow between working & counter electrodes.

Plot a cyclic voltammogram (current vs potential curve).

Symbol: s

Rate at which potential is varied during a cyclic voltammogram.

Faster scan rate leads to higher currents.

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What are each of these CVs examples of?

1) Potential Sweep

2) Ideal Capacitive Behaviour

3) Redox - Presence of anodic and cathodic peaks

4) Neg. potential - Hydrogen evolution reaction (at cathode), Pos. potential - Oxygen evolution reaction (at anode)

[image]

What are each of these?

1) Current Sweep

2) Ideal Capacitive

3) Typical capacitive (Ohmic drop caused by switching from charge to discharge).

4) Redox

1) Material intensity - Quantities of materials in kg per rated kW of generating capacity, to construct it.

2) Capital intensity - How much does it cost

3) Land intensity (m²/kW_^nom)

4) Construction energy intensity - how much needed for production.

5 - Construction carbon intensity (kg/kW_nom)

- The fraction of time that a power system operates at its rated or nominal power.

- Downtime for maintenance or fuel replacement. Unavailability of primary energy source.

Photovoltaic power (only 8-12%)

Requires daytime, clear skies, inclination of the panel to incoming radiation.

Worst - Biomass

Best - Fuel Cell, Oil & Gas, Nuclear, Geothermal

It is the efficiency of conversion of the primary energy source into electrical power.

For example PV is only 20%, as only 20% of incident radiation is converted to electricity.

Concentrated light is converted into thermal power by heating the working fluid.

This fluid transfers heat to water in heat exchanger, producing steam, which is then converted by a turbine into mechanical energy.

- They become permanently hard when heat is applied, even after subsequent heating (instead will char, burn or decompose).

- Strong primary bonds

- 59% of Co in DRC.

- 67% of graphite from China

- 91% of Li from Australia, Chile and Argentina

- Current Li reserves only enough for until 2030 if market growth continues as expected.

- Demand for graphite expected to grow tenfold by 2030, with a market deficit.

1) Short-circuiting - Mechanical abuse can damage the separator causing a short-circuit. This causes rapid discharge and heat generation.

2) Overcharging - Can lead to excessive deposition of Li ions in the anode, and release of oxygen which can react with flammable electrolyte.

3) Electrolyte Breakdown - Organic molecules in the electrolyte can break down during charging, forming CO₂. This can cause pressure build up and bursting.

- Safer.

- Offer higher energy AND power density.

- Higher current density and charging time.

- Prevention of dendrite formation of Li.

- No need for additional separator.

- Faraday in 1830s discovered conduction property of certain heated solids

- In 1960s, ionic transport in β-alumina discovered.

- In 1973, first discovered in a solid polymer

- In 1985, ZEBRA battery developed in SA, rechargeable molten salt battery.

Two main groups: 

Inorganic and organic solid polymers.

Advs:

- Sodium is 6th most abundant element, comapred to lithium reserves dropping.

- Sodium carbonate only $200 per ton whilst Lithium carbonate $6500 per ton.

- More cycles.

Disadvs:

- Li has higher magnitude standard electrode potential (vs. SHE), means higher voltage (up to >1.0V) and energy density.

- Ions are bigger meaning slower kinetics (slower charging) and more strain.

Hard carbon most commonly used, graphite is not effective as an insertion host. It is non-graphitisable, non-crystalline and amorphous.

[image]

Positive electrode - Sulphur

Negative electrode- Lithium

Pros:

- Sulphur is very abundant (5th most itw).

- High theoretical capacity

- Lightweight

Cons:

- Poor cycle life

- Reported capacities a lot lower than theoretical

- Low cell voltage and energy density

- Polysulfide Shuffle

- Sulphur requires conductive additives

- Li-S batteries rely on reduction of elemental sulphur into lithium polysulphides, then into Li₂S_x.

- The lithium polysulphides (LiPS) are soluble in liquid electrolyte, and migrate to lithium anode.

- When polysulfides reduced at anode, Lithium and electrons are consumed unintentionally.

Loss of active material :( Self-discharge :( Cycle life bad cause of it :(

- Helmholtz suggested the formation of an Electrical Double Layer at the interface between the electrode and electrolyte. 

- A layer of electronic charge at electrode surface and a single layer of counter-ions in electrolyte.

- In Helmholtz model, the EDL acts like a parallel plate capacitor.

- Does not account for interaction between the electrode and solvent (i.e. mixing and adsorption).

Gouy-Chapman model accounts for ion mobility in electrolyte, due to:

- Concentration gradient

- Electric field

Resulting in formation of diffuse layer.

Combination of Helmholtz model an Gouy-Chapman model:

1) Inner region of thickness, x, termed Stern layer.

2) Outer diffuse layer.

(1/C_S) = (1/C_H) + (1/C_GC)

[image]

- Supercapacitors store and deliver short bursts of energy, discharge much much faster but suitable for frequent stops.

- Quick charging system at designated stops (may be overhead or ground-based).

- Can also use regenerative braking, the kinetic energy from braking is converted back into electrical energy, increasing efficiency.

What is EDLC? 

Requirements and qualities

Electrical double-layer capacitance 

Capacitance generated from the electrostatic store of charge in the EDL.

- Requires high specific surface area (such as activated carbon).

- Very fast charge and discharge, works for millions of cycles. Works at low temps.

What are the two main types of pseudocapacitance? 

How does it differ from EDLC?

Surface redox and Intercalation.

Unlike EDLCs the charge-storage is not purely electrostatic.

Storage via Faradaic charge transfer. 

In conducting polymers and metal oxides.

Ions from the electrolyte partake in chemical reactions on the electrode surface (w/ transfer of electron).

These reactions store energy.

Despite this the system acts like a capacitor, if electricity is reversed the reaction goes backwards with quick energy release.

1) High costs

2) Limited capacitance and low electrical conductivity

3) Short cycle life

4) Limited to aqueous electrolytes with narrow potential window

[image]

What behaviours are shown by each colour Nyquist plot?

Green - Electrical double layer capacity

Blue - Pseudocapacitance

Red - Battery behaviour

Equivalent Series Resistance

It is the internal resistance inside a capacitor that causes energy loss and affects performance.

Occurs in batteries, and to a smaller extent pseudocapacitors.

It is caused by Charge Transfer Resistance (R_CT). Greater the radius the greater the value of R_CT.

It quantifies the resistance encountered by ions as they move across the electrode-electrolyte interface during charging/discharging.

Charge transfer rate or time constant (τ) can be estimated from peak frequency of the semicircle:

τ = 1/(2π*f_max)

- During charge (electrolytic) -> anode positive, cathode negative.

During discharge (galvanism) -> anode negative, cathode positive.

- Anode is often carbon-based (when intercalation is primary ion transfer process) e.g. graphite, due to its ability for intercalation, its stability and condutivity.

- Used as an additive at the cathode to provide a conduction path, plays no role in cell chemistry. Improves ionic and electrical conductivity.

The difference of electrical potential between two

terminals of a device when disconnected from any circuit

The number of charge and discharge

cycles a battery can complete before losing

performance.

Layer of copper, layer of cloth soaked with salt water, layer of zinc. This pattern can be repeated and stacked on top of each other. 

Individual cell is 0.76V

- Lead anode

- Lead dioxide cathode

- Sulfuric acid electrolyte (voltage dependent on concentration).

- Zinc anode. 

- Manganese dioxide cathode (with carbon rod) in porous pot.

- Porous pot is dipped in glass jar of ammonium chloride.

Gassner's cell was the first dry battery, using paste of ammonium chloride and gypsum electrolyte.

- Used zinc shell rather than a rod.

- More portable than the wet cell, and orientation didn't matter.

-Corrosion of zinc casing led to leaking of acidic electrolyte, meaning low shelf life.

- Hydrogen generated produces an internal

pressure, leading to rupture of case and leakage of solution.

1) Current collector - brass pin in the middle of cell.

2) Protective cap

3) Anode - Mixture of zinc powder and electrolyte (potassium hydroxide)

4) Separator - prevents migration of solid particles

5) Cathode - High purity manganese dioxide mixture + carbon conductor

6) Steel Can - Confines active materials and acts as the cathode's collecto

Pros:

- Good cycle life

- No electrolyte consumption

- Rechargeable

- Works at low temps

- Fast charge/discharge rates

Cons: 

- High self-discharge

- Low voltage (about 1.2V)

- Expensive

- Cadmium toxic & disposal hard

Nickel-metal Hydride (NiMH)

Longer life and less environmental damage.

SEI is a layer of lithium carbonate that forms in Li-ion cells on the negative electrode (graphite) due to reaction with the electrolyte.

It forms over the first few charging cycles and prevents further electrolyte breakdown whilst still letting lithium ions through.

- Pseudocapacitive electrode materials in supercapacitors

- Light harvesting materials in solar cells

- Semiconductor material in thin film transistors

- Electromagnetic material in LEDs

- Sensors and actuators

- Biosensing

- Drug delivery

- Tissue engineering

PANi can be used instead of carbon black as a conductive additive. Can also be used as a cathode material.

- They have promising psuedocapacitive capabilities, can be used in EDLC materials to enhance storage performance (but expensive, swelling and shrinking an issue and life cycle bad)

Chemical Vapour Deposition (CVD)

Gaseous Carbon passed through transition metal catalysts at high temp in a furnace. Creates high-quality CNT structures.

Single-Walled Carbon Nanotubes - 0.4-3nm diameter, length a few cm. $1000 per gram. (HUGE aspect ratio, more hazardous)

Multi-Walled Carbon Nanotubes - 2-100nm diameter, length in micron-scale. $200 per gram

They offer:

- Enhanced electrode/electrolyte contact due to high specific surface area

- High conductivity

- Hollow structure means more connection sites

- Lightweight

- Theoretical capacity 3x more than graphite (1000mAh/g achieved)

- More efficient intercalaction.

- Micromechanical cleavage, creates high-quality, large flakes

- Chemical vapour deposition (CVD), growth on substrates

- Liquid Phase Exfoliation (LPE), sonication of graphite in solvent with matching solubility or in water with surfactant, followed by centrifugation.

- Graphene Oxide (GO), Oxidation of graphite, followed by centrifugation and reduction

$50-$200 per kg

Mechanical exfoliation is highest price and quality (for research and prototyping).

Liquid phase exfoliation is cheapest and lowest quality, used for coatings, composites, inks etc.

- Flexible displays

- Energy storage devices

- Field-effect transistors

- PVs

- Sensors

- Polymer reinforcement

- Li-ion battery anode (capacity up to 1040mAh/g)

- Silicon anode has hugely impressive theoretical capacity (3600mAh/g)

-But the main issue is volume change, 3.2x increase when binded to lithium ions (lithiation), graphene can reduce this growth.

- Start with multi-layer graphene, add Si coating and add additional carbon coating via deposition.

[image]

- Use porous structures

- Prevent agglomeration using CNT as spacers, to bridge graphene sheets and increase conductivity.

- Graphene can buffer volume change of CP

- Graphene can provide a substrate for CP growth

- Can grow PANi nanowires on graphene oxide.

1st Gen have 20% efficiency, 4th Gen up to 60% efficiency.

Not necessarily better at absorbing particular wavelengths, but instead better at absorbing more wavelengths.

Based on crystalline silicon technologies:

Both monocrystalline and polycrystalline.

Also Gallium Arsenide (GaAs)

- Amorphous silicon (a-Si) and microcrystalline silicon (c-Si) thin film solar cells.

- Cadmium Telluride and Cadmium Sulfide (CdTe/CdS)

- Copper Indium Gallium Selenide (CIGS) solar cells.

Technologies based on newer compounds:

-Nanocrystalline films

-Active quantum dots

- Tandem or stacked multilayers of inorganics based on III-IV materials (GaAs/GaInP)

- Organic and dyed-sensitised solar cells

- Known as "Inorganics-in-Organics"

- Low cost of polymer thin films with stability of novel organic nanostructures such as nanoparticles and metal oxides.

Examples: CNT and graphene

Thermodynamic limit: 67-87%

Single band gap limit: 31-41%

- Abundant in the Earth's crust

- Stable and non-toxic

- Si technologies are well developed and so Si PVCs can be easily adapted into integration with these electronics

m-Si -> 24.4%

p-Si -> 19.9%

Grain boundaries and defects means worse material quality and more impurities.:

p-Si therefore has worse voltage and current

- Effect of recombination is higher in p-Si cells, leading to lower voltage.

- Incomplete carrier collection leads to lower current

28.8%

- Band gap is 1.43eV, close to ideal value for single-junction PVCs

- High absorptivity, only a few microns thick can absorb the usable sunlight spectrum corresponding to its band gap (crystalline cells would need to be 100 microns+)

- Allows versatile cell design, can combine with other III-V materials

- Resistant to radiation degradation

- Low temperature coefficients, less effected by operating temp.

- Cheaper than other Si solar cells

- Reduced amount of materials needed

- High absorption coefficient

- Can directly integrate into a higher voltage module, meaning reduced production stages vs. 1GEN

- Can use vacuum or non-vacuum processes

- Lower efficiency, best efficiency achieved is 20.3% for CIGS

- Light-induced degradation in first stages of outdoor use, higher degradation in outdoor uses (can generate current in the glass). Also environmental degradation

- Availability of some manufacturing materials not abundant.

- The lack of crystalline structure means a shorter life cycle, due to the formation of hole-electron recombination centres.

- Doping harder without crystalline structure, requires hydrogren.

- Efficiency only 10.2%, 12.7% for multi-junction

- Raw materials abundant and non-toxic

- Can use large area deposition techniques.

- High adsorption coefficient means only need to be a couple of microns thick

- Low-temperature processes can be used

1) Sheet, stainless steel foil -> cleaned

2) Insulating layer printed

3) Active a-Si:H layer deposited on reflector

4) Transparent conductive oxide (TCO) layer deposited

Laser cuts made to interconnect layers

5) Module encapsulation with metal grid

1) Substrate such as a metal or ceramic used to support the rest of the cell

2) Back contact covers it

3) CIGS layer grown via co-evaporation process

4) A buffer layer formed of a TCO on top of this

5) Anti-reflective coating on top to improve efficiency.

1) Direct reaction of Cd and Te at high temp in sealed quartz tube

2) Exposure of Cd solution to H₂Te under inert atmosphere

3) Addition of Cd in metal telluride solution

1) CdS layer is vapour deposited on TCO film

2) CdTe layer deposited on CdS layer

3) Laser cut through 3 layers to introduce module insulator

4) Additional cuts made to laser to add rear contact

5) Cell is encapsulated, wires connected, rear glass placed.

- Aiming for high efficiencies whilst using the thin layer deposition techniques of 2GEN PVCs and/or newer architectures and materials

- Non-toxic and very abundant materials, allowing for large-scale implementation

- Nanostructured and organic materials implemented to aim for 60% efficiency.

- Capture wider range of solar spectrum, charge collection optimisation.

- Work in low-light conditions (cloudy or indirect sunlight)

- Cells are mechanically robust

- Higher efficiencies at higher temperatures

- Low-cost

- Light-weight (glassless collector)

- The liquid electrolyte has temperature stability issues

- Contain volatile organic compounds that are toxic

1) Transparent anode manufactured with a glass sheet, treated with TCO

2) Mesoporous oxide (TiO₂) deposited on anode for better conduction

3) Monolayer of charge transfer dye bonded to mesoporous oxide layer, enhance absorption.

4) Electrolyte in organic solvent, improve light regeneration

5) Cathode coated with catalyst as cathode. Facilitate electron collection.

Benefits of quantum dot PVCs?

Efficiency?

- Good power-to-weight ratio

- High efficiency

- Mass and area savings and flexibility, can be small

- Low power consumption

- Versatile

- Can be used in complete buildings (i.e. windows)

11% efficiency, 17% with doping

The absorber material is water soluble and so is prone to degradation in a moist environment.

- OPVCs use organic materials rather than semiconductors.

- Like with PVCs, light excites electrons into a higher energy state but:

They rely on exciton diffusion and dissociation. 

- The donor material absorbs photons, creating excitons. An electric field separates these into electron-hole pairs. The acceptor acquires the electrons from the dissociated EHPs.

Polymer Solar Cells

Made of Indium Tin Oxide (ITO) conductive glass covered by a polymeric hole transporting layer, an active layer, an electron transport layer and a low work function metal electrode like Al.

Sandwich connection of organic materials between two metallic conductors (typically Al and ITO).

Organic layer with highest electron affinity and ionising potential values is the acceptor, the other is the donor.

- PVSC excitons do not need to have a long lifetime. The absorption of photons practically results in the generation of free charge carriers

- Energy losses due to exciton generation, their movement and dissociation are avoided.  

- Compose of multiple p-n junctions made of different semiconductor materials

- Each produces current in response to different wavelengths of light, increasing conversion efficiency.

- Maximises photon use.

[image]

Combining the low cost and flexibility of polymer thin-films with the good stability of nanomaterials.

Means cheaper manufacturing than solution-processable devices, but with the improved charge dissociation and transport of nanoparticles.

G is almost transparent and so only absorbs 2.3% of radiation, meaning difficulty capturing photons. 

Must be doped first.

Real (Z') and Imaginary (Z'') parts of impedance Z(ω). 

Provides insight into the mechanism, mass transfer and kinetics.

Shows phase shift (φ) and the magnitude of impedance (|Z|) with respect to an applied frequency (f).

Shows frequency-dependent behaviour of sensors, filters, transistors etc.

Impedance when diffusion effects completely dominate

electrochemical reaction mechanism; current is 45° out of phase with potential; real and imaginary components of impedance vector are equal at all frequencies midway between a resistor (0° phase shift) and a capacitor (90° phase shift).

A model for a diffusion-controlled Faradaic reaction on a planar electrode; series combination of equivalent series resistance (ESR, R_S) with double layer capacitance (C_DL) in parallel with charge transfer resistance (R_CT) and Warburg impedance (W) in series.

[image]