Multi-junction cells
MBE growth
> 40% efficient
Expensive
Single crystal Si
>20% efficient
expensive
Thin film cells
>10% efficient
Less expensive
Toxic materials
Polymers
<5% efficient
Cheap
Goal for next generation solar cells:
Efficiencies greater than Si with low cost (low temperature) processing
Solar Spectrum and Jsc
The photovoltaic (PV) industry defines two, and only two, standard terrestrial solar spectral irradiance
distributions. The two spectra define a standard direct normal spectral irradiance (AM1) and a standard
total spectral irradiance (AM1.5). The standard conditions selected were considered to be a reasonable
average for the 48 continguous states of the United States of America (U.S.A.) over a period of one year.
The tilt angle selected is approximately the average latitude for the contiguous U.S.A.. The receiving
surface is defined in the standards as an inclined plane at 37° tilt toward the equator, facing the sun (i.e.,
the surface normal points to the sun, at an elevation of 41.81° above the horizon)
Solar Cell Equation
Calculating the Maximum Power
The energy Em is the energy of one photon, which is converted to electrical energy at
the maximum power point.
Materials Abundance
Solar Cell Technologies
First Generation:
Single crystal silicon (c-Si)
Second Generation: Lower Cost
Amorphous and Polycrystalline Si
Cadmium Telluride
Copper Indium Gallium DiSelenide (CIGS)
Photoelectrochemical Cells
Organic Solar Cells
Dye Sensitized Cells
Luminescent Concentrators
Third Generation: Higher Efficiency
Quantum Dot Solar Cells
Tandem Solar Cells
Thermophotovoltaics
CIGS and CdTe: PN Junctions
CIGS Solar Cells
(Miasole, Nanosolar)
Cu(In,Ga)Se (~2mm)
Mo bottom contact
CdTe Solar Cells
(First Solar)
ZnO
Transparent
Conductor
(200nm)
CdS
Buffer layer
(~50nm)
• High efficiency (12 – 17% module efficiency)
• Lower temperature processing (~400oC)
• Metal foils for substrates
CdTe (~2mm)
Al contact
Lower cost / watt
Why use Nanomaterials and Organics for PV?
Low Cost combined with High Efficiency
Monodisperse NP
with high PL efficiency
can be very expensive
Low Synthesis Costs: Nanomaterials can be grown
near ambient temperature using colloidal
synthesis or near atmospheric deposition
processes.
Low Manufacturing Costs: Nanomaterials can be
deposited using solution (print) based
processing under atmospheric conditions
Low Materials Cost: Nanomaterials enable the use
of less material than traditional thin-film solar
cells.
NP solutions
m
or ALD
Nucleation
& growth
m
High Efficiency Nanoparticle PVs
h>2Eg
Bulk
MEG
MEL
Energy lost as heat
Double current
Double voltage
Polymer Donor:Acceptor PV Research at UCSC
Donor: p-type Polymer (polythiophene and their derivatives)
Acceptor: metal oxide (TiO2), n-type polymer (CN-ether-PPV), fullerene (PCBM)
0
2
J (mA/cm )
-2
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
-4
PEDT only
TiOx-sg layer
TiOx-np layer
CN-e layer
CN-e blend
PCBM blend
-6
-8
0
0.2
0.4
0.6
Voltage (V)
0.8
1
Arango, APL 1999, Adv. Matl. 2000,
Breeze, PRB 2001, SOLMAT 2004,
Chasteen, JAP 2006, SOLMAT 2008
Haerter, APL 2005
Polymer-nanoparticle Hybrid Devices at UCSC:
CdSe/P3HT
Organic Solar Cells: Donor-Acceptor Heterojunctions
Status of Hybrid PV in 2008
(compared to year in which research started)
CdTe/CdSe nanoparticle pn junctions
Ingrid Anderson, Jeremy Olson, Yvonne Rodriquez, Lily Yang
T

QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
No buffer layer
Best P ~3%
Au or Al electrode
CdTe nanoparticle Schottky junctions
Jeremy Olson, Ingrid Anderson, Yvonne Rodriquez, Lily Yang
CdTe nanoparticle Schottky junctions
Jeremy Olson, Ingrid Anderson, Yvonne Rodriquez, Lily Yang
5% Power efficiency is highest reported in devices made from a single layer of
solution deposited nanoparticles
Luminescent Solar Concentrators (LSCs)
• LSCs use an inexpensive material to
collect photons, down-shift and concentrate
the photons, and then convert it to power
using standard PV
1
1
1-Transmission
0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2 mm cell
0.2
0
Relative Photoluminescence
1.5 mm cell
• Efficiency of Si @ 900 nm is ~50%
+ Optical efficiencies of 40%, enable
Power Efficiencies exp ~ 20%
• One can utilize highly scalable
window-based manufacturing for
inexpensive solar cell production
0
400
500
600
700
800
900
wavelength (nm)
Goal: to develop a stable inexpensive material that can absorb a majority of the solar spectrum and
readmit the photons to wavelengths where PVs have peak efficiency, while minimizing self
absorption.
LSCs based on QDs and Polymers
Veronica Sholin, Jeremy Olson (Funding: PIER-EISG)
Red F
LSCs: Role of Self-Absorption
LSCs: Overall Efficiency
Experiment
LSC = opt* Si
opt = PL* abs*  WG
Simulations
New IR-absorbing polymers, combined with greater PL QY, offer opportunities for higher opt
Improving LSC Efficiency through control over nanostructure
Mike Griffo, Sue Carter, Physics (Funding: ACS PRF)
opt = PL* abs*  WG
The PL can be substantially enhanced via
coupling to plasmons on metallic NP surfaces
Improving LSC Efficiency through over Polymer
opt = PL* abs*  WG
The abs can be substantially increased
using a better polymer system
Normalized Absorption & Photoluminescence
The WG can be substantially increased
using polarized emission
Polyfluorenes and liquid crystalline polymers
emit preferentially perpendicular to backbone.
Realamine
Abs
PL
300
400
500
600
700
wavelength (nm)
opt = 29%
800
900
or the sun
Theoretical Power Efficiencies > 65%