Chapter 4. Quantum Dot Solar Cells

Introduction to Chemical Convergence for Energy & Environment

Chapter 4. Quantum Dot Solar Cells

Spring Semester, 2011

Kookheon Char

What Are Quantum Dots, Rods, or Wells?

 Semiconductor nanostructures (nanocrystals) in several nanometer range (approx. 1,000 ~ 10,000 atoms)

 Unique physical & chemical properties:

- Large surface-to-volume ratio - Tunable bandgap

- Quantum behavior in electronic properties . .

.

Unique Optical & Electrical Properties

Tunable Band Gap

Quantum

Confinement Effect (QCE)

Wide Absorption Range

VIS

IR

UV

A. J. Rogach et al., Adv. Func. Mater. (2002)

Multiple Exciton Generation (MEG)

Unique Transport Phenomena

Preparation Process: Wet vs Dry

Vacuum Deposition & Conventional Lithography (i.e., MOCVD, MBE, Photolithography, …)

InAs Quantum Dots

on GaAs Substrate GaAs/AlGaAs Quantum Wells Molecular Beam Epitaxy (MBE) Device

Wet Chemistry (Solution-Based Synthesis)

InAs Quantum Rods CdSe Quantum Dots

S. Kan et al., Nat. Mater. 2, 155. (2003) A. P. Alivisatos, Science 271, 933. (1996)

http://iop.ncl.ac.uk/research/dot.php B. Park, Nano Device, Lecture Note (2008)

QD Applications

Gao et al., Nature Biotech. (2004)

Light Emitting Diodes

Bio-Markers Solar Cells

Passive-Type Device (PL Device) Active-Type Device (EL Device)

Combined with Conventional PV Cells (w/ DSSC, OPV, Schottky type, …)

Bio-imaging

(IR emitter, low

photobleaching)

Part I:

Physical Aspects of Quantum Structures

From Atom to Bulk Materials

P⁺

Electron wave function

Cross-section of probability density

1s 2s 2p 3s 3p

Energy States of Atomic Orbital (AO)

Atom Molecule

Energy States of Benzene Molecules (Molecular Orbital, MO)

Bulk

Valence & Conduction Band

Formation of Diamond

Size Dependent Properties

 Size Dependent Physical Properties

 Optical Properties

- scattering, plasmonic effect, …

 Electronic Properties

- bandgap, electronic transition, carrier transport, …

 Melting Point (T

~ 1/r)

 Heat Capacity (C

> C

)

 Magnetic properties - Fe, Co, Ni, Fe

O

, …

 Reactivity

- Surface selective adsorption, reaction

Milk Gold Colloid Solution

Melting Point Depression

D(E )

Energy

D(E )

Energy

D(E )

Energy

Density of State (DOS) depending on dimensionality

dot rod well

 Effect of Ratio of Interfacial Volume to Particle Volume

2r

Sphere, r Aspect ratio = 1

δ = t / r 2r

l

Rod (Prolate), 2r < l Aspect ratio = l / 2r > 1

δ = t / r 2r

h

Plate (Oblate), 2r > h Aspect ratio = h / 2r < 1

δ = 2t / h

The ratio of interfacial volume to the particle volume (V_interface/ V_particle) as a function of the particle aspect ratio and δ (ratio of the thickness of the interface to the smallest dimension of particle) For the same volume fractionof NPs:

mean particle – particle separation ~ r total internal interfacial area ~ 1 / r number density of constituents ~ 1 / r

V

/ V

↑ as aspect ratio → 1

& δ → ∞

Reduced object size increases interfacial area dramatically !!

Calculated interfacial area per volume of particles (in nm^-1)

E. L. Thomas, Adv. Mater. 17, 1331. (2005)

Increased Surface to Volume Ratio (I)

 Example: Iron Nanocrystals

Nanoscale Materials in Chemistry, Wiley (2001)

Increased Surface-to-Volume Ratio (II)

Spherical Iron Nanocrystals

J. Phys. Chem. (1996)

Melting Point Depression

CdS NPs

T_b: bulk melting temperature

T_m: melting temperature for a particle of radius R L: molar latent heat

γ: surface tension ρ: density

Relationship between

lattice parameter (a) and surface tension of solid

(κ = 1.56 X 10^-11 m²N^-1)

γ

– γ

: 0.42 N m

From the a – γ relation

γ

for bare nanocrystal : 2.50 N m

γ for bulk crystal : 0.750 N m

Increased Surface Tension

Melting Point Depression

Low Dimensional System: between Molecule & Bulk State

A. P. Alivisatos, Science, 271, 933 (1996)

 Change in Density of State (DOS) Corresponding to the Number of Atoms

Metals (i.e., Au NPs)

Semiconductors (i.e., Si NPs)

 E

centered in a band

 Infinitesimal energy spacing around the Fermi level

 Not drastic change in optical & electronic properties

 E

centered in a bandgap

 Drastic change in band edge as a function of size

 Large Variation of Optical & Electronic Properties in Size

Density of States Corresponding to Dimensionality

Density-of-State Shape Nano-Objects

0D

1D

2D

20 nm 5 nm

50 nm

D(E )

Energy

D(E )

Energy

D(E )

Energy

Quantum Dot

Quantum Rod

Quantum Well

Simple Description: Electron Gas in a Solid

 Ideal 3-D Electron Gas

Schrodinger equation for a free (V = 0) electron in 3-dimentional space

Periodic boundary condition for a cubic solid w/ side L

K. Barnham et al., “Low-Dimensional Semiconductor Structures”, Cambridge University Press (2001)

Solution:

Ideal 3-D Electron Gas (I)

For a cubic solid w/ side L, the allowed quantum states are evenly distributed in k- space with one state taking the volume, (2 π/L)

Number of states in a volume element d Ω

Volume for states with energy E ~ E+dE

Volume for states with energy E ~ E+dE

Ideal 3-D Electron Gas (II)

Two electrons (up spin, down spin) can be accommodated in each state

Density of State (DOS) per unit volume

Bulk Semiconductors

Ideal 2-D Electron Gas Ideal 1-D Electron Gas Ideal 0-D Electron Gas

Real Electron Gas in the Finite Dimension

Effective Mass Approximation

 Ignoring periodic potential by atoms in lattice…

 Limited at the conduction band minima &

the valence band maxima

E-k Diagram of Bulk Silicon (Bloch Theorem)

Φ

(r) ~ Φ(r)u(r)

Ideal Square Well (I)

Infinite square well:

Schrodinger equation for z-direction

Ideal Square Well (II)

Lowest energy of the system

Higher quantized energy levels

Density of States (DOS)

DOS of bulk

DOS of Quantum Wells

Students: Please try to calculate 1-D & 0-D systems!

Unique Properties of Quantum Structures

Quantum Dot as a Simple Model…

1.5 nm

<001>-oriented CdSe QD synthesized by Wet Chemistry

C. B. Murray et al., Annu. Rev. Mater. Sci. 30, 545 (2000)

increase in E

RT 10 K

Quantum Confinement Effect

Characteristic Length L

< Bohr Exciton Radius >

Controllable Bandgap by Tuning in Size

R e m

m R Bulk h

E QD E

h e g

g

0 2 2

2

4 8 . 1 1

1 ) 8

( )

( ^ _ ^ 

 



 





Optical Transition in Quantum Dot (I)

O. I. Micic et al., J. Phys. Chem. B 101, 4904. (1997)

 Absorption Characteristics:

- Electronic transition from ground state to discrete valence states

- Discrete near-edge states & continuous far-edge states  transition probability - Large extinction coefficient

CdSe QDs Size Dependent Electronic Transition of CdSe QDs

ε X 10

cm

M

@ 1

ex cit on pea k

Size (nm)

Molar Extinction Coefficient

Optical Transition in Quantum Dot (II)

Al. L. Efros et al., Annu. Rev. Mater. Sci. 30, 475. (2000)

 Emission Characteristics:

- Hot carriers are thermalized to the band-edge state.

- Large stokes shift (exciton-phonon interaction, carrier-carrier interactions, band- edge exciton fine structure due to anisotropy, …)

- Broadening caused by size inhomogeneity, exciton-phonon interactions, surface traps

Thermal Relaxation (coupled with phonons)

Excitation

hv' hv

Non-degenerated band edge state

Optically active state

Stokes Shift

Optical Transition from Surface State

hv hv’’

Photon w/ low energy Non-Radiative Process

Surface Passivation

hv hv'

Band-Edge Transition

emission from surface states

Undesired Electronic Transition

Transport Phenomena in Quantum Dot Solids

Interaction btw. Quantum Dots

Similar electronic structure compared w/ atom

Weak Coupling (hΓ << k

T) Hopping (Coulomb Blockade)

Strong Coupling (hΓ >> k

T) Conduction (thru Miniband)

Miniband Formation

Artificial Atom

Coulomb Blockade σ (conductivity) ↑

as β (coupling btw. QDs) ↑ & Δα (Disorder) ↓

Dynamics of Carriers in Quantum Dots

Hot Carrier Extraction Solar Cells

Carrier Multiplication

(Multiple Exciton Generation: MEG) Solar Cells

Thermalization of Carriers thru Phonon Emission

Efficiency drop from the thermodynamic limit to

1 electron / 1 photon limitation (Schokley – Queisser Limit)

~ ps

Discrete DOS in CB ( Phonon Bottleneck)

Energy Transfer of e

to Hole States

vs. Multiple Excitons by

Large Energy (hv > n E

)

Part II:

Synthesis of Quantum Structures

Based on Wet Chemistry

TEM Images of Various Nanocrystals Synthesized by Wet Chemistry

CdSe/CdS NRs CdSe/CdS Tetrapods

CdPt₃-Au Dumbbells

CdS-Au₂S Rods Au-CdSe-Au Rods

PbSe Nanowires Iron Oxide hollow

spheres PbSe Cubes CdTe Tetrapods Au/PbS Core/Shell

Candidate Materials for Semiconductor Nanocrystals

Bandgap (E

) of Various Semiconductor Materials

Vis. Range (for LED)

Solar Spectrum

(for solar cells)

Requirements for Efficient Light Harvesting Materials

 Size & Shape

 1.1 eV < E

< 3 eV

 rods, tetrapods, dendritic shape

 Surface Treatment

 Efficiency & Stability

 Wide Absorption Range (VIS ~ IR) Facilitated Charge Transfer

 Exciton Dissociation & Extraction

IR VIS

 Band Position

 Type II bandgap

 Decrease in R

& Oxidation

Conventional Synthetic Route

 Pyrolysis Method to Prepare High Quality CdSe QDs

Me

Cd in TOP

 Nearly monodisperse in size

 Well-resolved optical transition at RT

 Wurzite, Zinc blende, or Rock salt crystals Hot injection

at high temp +

TOPSe, TOPTe

TMS

Se. TMS

Te

or TOPO

Φ

~ 10 % at RT

~ 100 % at low T

C. B. Murray et al., J. Am. Chem. Soc. (1993)

Wurzite crystal structure

11.5 nm

TOP: tri-n-octylphosphine

TOPO: tri-n-octylphosphine oxide

Surface Passivation

 Surface-State Passivation by Inorganic Shells

X. Peng et al., J. Am. Chem. Soc. (1997)

Core/Shell

Core

B. O. Dabbousi et al., J. Phys. Chem. B (1997)

CdSe/CdS QDs CdSe/ZnS QDs

470 480 520 560 594 620 nm

Epitaxial Growth of ZnS or CdS Shells with Several Monolayer Thickness (1 ~ 2 monolayers)

 Single-Step Synthesis for Cd

Zn

Se

S

Quantum Dots (Red/Green)

Synthesis of Highly Luminescent RGB Quantum Dots

 Low QY and photostability

 From violet (410 nm) to blue (460 nm)

 Narrow emission (fwhm < 30 nm)

 High QY (up to 80 %)

 Improved photostability

Cd_1-xZn_xSe_1-yS_y

Cd(OA)₂ Zn(OA)₂ TOPSe TOPS

core core

core

core

core

core

Cd

Zn

Se

S

CdSe

ZnS

K. Char et al., Chem. Mater. (2008)

K. Char et al., Chem. Mater. (2008) abruptinterface

diffuseinterface

 Infusion-Assisted Synthesis for Cd

Zn

S@ZnS Quantum Dots (Blue)

CIE Indices of RGB QDs

Wavelength (nm)

350 400 450 500 550 600 650 700

Intensity (a. u.)

Core/Shell Structured RGB QDs

> 70 % > 70 % > 70 %

 Straightforward and efficient synthesis

 Wide absorption & high exctinction coefficients

 Narrow spectral bandwidth (FWHM < 35 nm)

 High QY (> 70 %) & photostability

 Scale-up capability (in gram scale)

G

B

R

3 g

RGB Quantum Dots for Light-Emitting Materials

Synthesis of Monodisperse Nanoparticles (I)

 “Burst” Nucleation and Slow Growth

LaMer Plot to separate nucleation and growth…

J. Park et al., Angew. Chem. Int. Ed. 46, 4630 (2007)

State I: Supersaturated but no precipitation

State II: Burst nucleation Large energetic barrier

Enough supersaturation

to overcome nucleation barrier

State III: Growth stage

Size focusing / defocusing

surface (  > 0) & volume (  G

< 0) component

Dissolution Growth

High S (supersaturation) for small critical radius

Please try to derive the critical radius

Thermodynamically & kinetically controlled growth

Synthesis of Monodisperse Nanoparticles (II)

 Surface Energy

Solvent (coordinating or non-coordinating) Surfactants (Surface binding)

 Temperature

 Supersaturation

Numerical Simulation on the Growth Behavior corresponding to:

Surface Energy Temperature Supersaturation

 Hot-Injection Method

Stabilization of Nanocrystals in Medium

 NO-NO Interactions

 Van der Waals interactions

 Related to Dimensionality, Relative Orientation, and Distance

Crossed Cylinders Parallel Cylinders Spheres



 





 ₂

1 2

1 1

~ R R

R R W D

2 / 1

2 1

2 1 2 /

~ 3 



 





R R

R R D W L





~ 1 RR W D

Three kinds of stabilizations are possible…

 Massive Aggregations possible!!

Steric Stabilization

w/ noninterpenetrating polymers (organic layers) adsorbed on

NP surfaces

Depletion Stabilization

w/ free polymer medium Electrostatic Stabilization w/ Coulombic repulsive force

δ⁺ δ⁺

δ⁺ δ⁺

δ⁺ δ⁺

δ⁺ δ⁺ δ⁺

δ⁺ - -

-

- - - - -

- - - - - - - -

-- -

- - -

- -

-

- -

+ +

+ +

+

+

+

Oligomeric / Polymeric Surfactants w/ amine, carboxylic acid, phosphonic acid, thiol functionalities

Shape Control of Colloidal Nanocrystals

 Main Factors for Shape Control

 Surface Energy

 Crystalline Phase

 Growth Rate

 Surfactant

 Growth Temperature

Seed-Mediated Solution-Liquid-Solid Growth Oriented Attachment

Kinetically Induced Anisotropic Growth

Seed-Mediated SLS Oriented Attachment Kinetic Shape Control

Seed-Mediated Solution-Liquid-Solid Growth

Phase Diagram of AuGe Alloys

Alloy formation  Supersaturation (similar to VLS growth in vapor phase)

Decomposition of Precursors

Ge Nanowire Grown from a Seed

Oriented Attachment

High Energy Facets

Large Surface Energy

minimizing ΔG by aggregation

Oriented Attachment

Octahedral Nanocrystal

(ex) PbSe Nanocrystals

Star-Shaped Nanocrystal Hexahedron Seed

Kinetic Shape Control

G: Growth Rate S: Surface Energy Reactivity Difference

along with each crystal facet

Shape Control of CdSe Nanocrystals

Control by Thermal Energy Control by Monomer Concentration

Y-. W. Jun et al., Angew. Chem. Int. Ed. (2006)

Part III:

Quantum Dot Based Solar Cells

Classification of QD Solar Cells

QD - Metal(or Schottky) Junction System

P. V. Kamat, J. Phys. Chem. C 112, 18737. (2008) A. J. Nozik, Physica E 14, 115 (2002)

QD – Conducting Polymer BHJ System

QD Sensitizer System

and other variations in PVs...

Survey of Nanocrystal-Based Photovoltaic Devices

CdSe NCs/PCPDTBT Al/LiF/BH/PEDOT:PSS/ITO 9.02 0.674 0.51 3.13% (AM1.5) 55%/480 nm 2010

QD–Metal Junction Solar Cells (I)

 Schottky Junction vs. Ohmic Junction

Φ

> Φ

V

Φ

E_F

Φ

< Φ

Schottky Contact (n-type)

E_F

V

: built-in potential Blocking contact

Ohmic Contact

No barrier to conduct from semiconductor to metal

Metal

Φ_m Φ_{s, n}

Semiconductor (n-type)

E_F E_F

Metal

Φ

Φ

Semiconductor (n-type)

E_F E_F

Vacuum level

Vacuum level

How about p-type Schottky contact ?

QD–Metal Junction Solar Cells (II)

 Fabrication and Surface Modification

HS-CH

-CH

-SH 1 um

Spin-Cast Film (QD Superlattice)

Crack Formation

Disordered w/o Crack

SAXS & WAX Diffractogram

LbL Dip-Coating (Glassy Solid)

Enhanced dipole

-induced dipole interaction Crosslinked w/EDT

Crosslinked w/EDT

Spin-Casting  Superlattices but large volume contraction

LbL Dip Coating

 Glassy solid but small volume contraction

Increase in

dielectric constant

Wavefunction

delocalization

QD–Metal Junction Solar Cells (III)

 Schottky-QD PVs Covering Infrared Region

J. M. Luther et al., Nano Lett. (2008)

~ 300 nm PbSe NCs Xlinked w/ 1,2-ethanedithiol (EDT)

Ca / Al

I-V Characteristics EQE vs. wavelength

Thickness Effect QD Size vs. V

Φ

vs. V

η ~ 2.1 %

pinned Fermi level

QD–Metal Junction Solar Cells (IV)

 Operating Mechanism in Schottky-Type QD Solar Cells

Ohmic contact Schottky

contact

Region

Relevant thickness

(nm)

Absorption (%)

IQE (%)

Contribution to overall EQE

(%)

Depletion (W) 65 13 > 90 > 12

Quasi-

Neutral (L_QN) 145 30 65 20

*PbSe QDs w/ benzenedithiolsas molecular linkers

Carriers Mobility (cm²/Vs)

Recombination lifetime (μs)

Drift length (μm)

Diffusion length

(nm)

Electrons 1.4 X 10^-3 > 13 8.5 220

Holes 2.4 X 10^-3 > 13 14.5 285

 Effect of Thiol Linker on Device Operation & Stability

 Surface passivation

 Decrease in distance btw. QDs

 Solution process capability (multiple depositions possible)

12 mW / cm² at 975 nm

High carrier mobility & rectifying junction

are responsible for the photovoltaic effect

QD–Metal Junction Solar Cells (V)

 World Best Schottky-Type QD PVs: PbSe

S

QD Solar Cells (Alivisatos, UC Berkeley)

W. Ma et al., Nano Lett. 9, 1699 (2009) Bright-field TEM image Energy-Filtered TEM

Blue: Se Red: S

Bandgap tuning through chemical composition change

η = 3.3 %

J

= 14.8 mA/cm

V

= 0.45 V FF = 0.5

ITO/PbSe

S

w/ Benzenedithiol / Al

increase in

electonic coupling

difference in

surface states

QD–Conducting Polymer BHJ Solar Cells (I)

Acceptor Donor

Thermalization

V

+

-

-

+

-

-

+

-

+ +

hv Carrier

transport

Bandgap & Offset / Charge Transport / Interfaces In the Case of Organic (BHJ) Photovoltaics…

 Low bandgap donors

 Light absorbing acceptor w/ suitable bandgap

 Bandgap Engineering

 Efficient Charge Carrier Transport

 Materials w/ high mobility

 Well-ordered nanostructure

QD – Conducting Polymer Hybrids

 High extinction coefficient

 Moderate hole mobility

 Solution process capability

 Patterning capability

 High extinction coefficient

 High electron mobility

 Band gap & position tunability

 Solution process capability

QD–Conducting Polymer BHJ Solar Cells (II)

 ZnO / MDMO-PPV System

W. J. E. Beek et al., Adv. Mater. 16, 1009 (2004) MDMO-PPV

ZnO NPs (D ~ 5 nm) 20 nm

Band Diagram of ZnO/MDMO PPV System

PL Change as a Function of wt % of ZnO J-V Characteristics

V_OC= 0.814 V

J_SC= 2.40 mA/cm² FF= 0.59 η = 1.6 % 0.71 sun equivalent

Photoinduced Absorption (PIA) spectrum Time-Resolved Pump-Probe Spectroscopy At 80K, excitation at 2.54 eV

modulated by 275 Hz

Pump beam:

510 nm, 500 Hz, 54.7^o

85 % of PL is quenched

by radical cation

QD–Conducting Polymer BHJ Solar Cells (III)

 PbSe / P3HT System

Band Diagram of PbSe/P3HT System Photocurrent & Absorption of Hybrid Film

Contribution by PbSe for Absorption

V

= 0.35 V

J

= 1.08 mA/cm

FF= 0.37 η = 0.14 % under AM1.5G Illumination

 Absorption by PbSe QDs

 Absence of interconnection btw. QDs

 Hybrid Nanorod-Polymer Solar Cells

W. U. Huynh et al., Science 295, 2425 (2002) d = 7 nm

7 nm X 30 nm

7 nm X 60 nm η = 1.7 % V_OC= 0.7 V I_SC ~ 4 mA/cm² FF = 0.4

 Quantum Nanorods

 Light absorption

 Transport

QD–Conducting Polymer BHJ Solar Cells (IV)

 Hyperbranched CdSe / P3HT System

Hyperbranced CdSe Device Structure

Inhomogeneous

Morphologies of HyperbranchedCdSe/P3HT Film

500 nm

η = 2.18 % AM 1.5G

 Enhanced percolation btw. CdSe & P3HT

 Practical advantage in fabrication and processing

QD – Conducting Polymer BHJ Solar Cells (V)

NR HB

NR HB

NR HB

contributions from CdSe (660 ~ 750 nm)

 CdSe / PCPDTBT (Low E

Polymer) System

S. Dayal et al., Nano Lett. (2010) CdSe Tetrapod

PCPDTBT (Low E_g ~ 1.4 eV)

Absorption at NIR combributed by PCPDTBT

* 90 wt% of CdSe

Contribution of CdSe to light absorption ~ 34 %

QD–Conducting Polymer BHJ Solar Cells (VI)

QD Sensitized Solar Cells (I)

 Configuration of QD Sensitized Solar Cells

FTO / TiO

:QD / Electrolyte / Cathod

 QD Deposition onto TiO

electrode - Chemical bath deposition (CBD)

- Successive ionic layer adsorption and reaction (SILAR) - Linker-assisted adsorption (LA)

- Direct adsorption (DA)

Direct growth of QDs onto TiO

Deposition of pre-synthesized QDs

QD Sensitized Solar Cells (II)

I. Robel et al., JACS 129, 4136 (2007)

 Charge Transfer Properties Depending on QD Size

Fast recovery of bleaching

k

= 1/τ

– 1/τ

τ: bleaching recovery lifetime log k ~ (driving force)

Driving force ~ -ΔG (energy difference btw. acceptor & donor)

Linked w/ TiO₂ Linked w/o TiO₂

QD Sensitized Solar Cells (III)

 Nanostructure Control of Photoanodes

particulate film

nanotubes

linked w/

mercaptopropionic acid (MPA)

Binding to QD

Binding to TiO₂

Sythesized QDs

TiO₂

particulate film

TiO₂ nanotubes

QD Sensitized Solar Cells (IV)

H. Lee et al., Nano Lett. 9, 4221(2009)

 CdSe/CdTe System Prepared by SILAR Approach

Cd

TiO

Se

or Te

TiO

/CdSe/CdTe

Favorable hole transfer Diminished charge recombination

recombination rate

electron diffusion length

w/ solid electrolytes

QD Sensitized Solar Cells (V)

 CdS/CdSe System Prepared by CBD Approach

CBD Cycle

High driving force for both e

Injection & h

recovery

ZnS: Passivation Layer to protect photocorrosion

η = 4.22 %

(world record)

All-Inorganic QD Solar Cells

I. Gur et al., Science 310, 462 (2005)

CdSe CdTe

40 nm 40 nm

Type II

charge-transfer junction - 4.79 - 4.12

- 6.64 - 5.85

Spin-casted film

1 μm

Glass

ITO

CdTe CdSe

Ca 20 nm / Al 80 nm

Alumina (2 A)

After sintering

Before sintering

η (%) V

(V) I

FF

2.9 0.45 13.2 0.49

AM 1.5G 100 nm

100 nm

*Sintering at 400 ^oC w/ CdCl₂

 Stable under Air (~13,000 min)

 Operated by Donor-Acceptor Mechanism (not Schotkky type)

Thursday, November 19, 2009

A. P. Alivisatos

(Lawrence Berkeley National Laboratory, USA)

Thin-Film Solar with High Efficiency

Solexant is printing inorganic solar cells with nanomaterials

QD Solar Cells with Semiconductor Nanorod Inks

Expected Price

1 $ / W(Module), PCE > 10 %

Current Status for Commercializing QD Solar Cells