semiconductors and photonics for energyfisica.unipv.it/dida/congressino2018/andreani.pdf · ∼94%...
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Physics Department, University of Pavia
http://fisica.unipv.it http://fisica.unipv.it/nanophotonics
Lucio Claudio Andreani
Dip.to di Fisica, Università di Pavia, 13-09-2018
Semiconductors and photonics for energy
OUTLINE
1. Introduction: energy & climate (in a bad mood)
2. Solar cells: towards the efficiency limits
3. Silicon photonics & optical communication
4. Conclusions
Global temperature increase
Earth’s surface temperature has increased by ≈1 °C over pre-industrial levels.This is correlated with cumulated CO2 emission, mainly due to the use of fossile fuels.
Conclusions from Intergovernmental Panel on Climate Change, http://www.ipcc.ch/
www.climatecentral.org
Global primary energy demand & related CO2 emissions by scenario
450 scenario = limit global temperature increase in 2100 to 2 °C above pre-industrial levels, by keeping CO2 concentration in atmosphere below 450 ppm
International Energy Agency (IEA) – World Energy Outlook, 2016
Global energy-related CO2 emissions & additional CO2 abatement in the 450 scenario
450 scenario requires strong increase in energy efficiency & use of renewables
IEA – World Energy Outlook, 2016
Grid vs solar electricity: grid parity…?
… yes, reached in many countries! But depending on solar irradiation & on grid market
EU-JRC PV Status Report 2017
Solar cells: towards the efficiency limits
Marie Curie action FP7-PEOPLE-2010-ITN 264687 “PROPHET”
Fondazione CARIPLO "Nanophotonics for thin-film photovoltaics"
ENI SpA "Fotonica per sistemi fotovoltaici basati su concentratori fluorescenti"
RSE SpA "Nanostructured antireflectioncoatings for multijunction solar cells"
Participants: M. Liscidini, M. Galli, M. Patrini, A. Bozzola, S. Flores, P. Kowalckzewski, M. Passoni, S. Rafizadeh, G. Timò, E. Achilli, L. Lavit…
Detailed balance limit to the efficiency of single-junction photovoltaic cells
Shockley and Queisser, JAP 32, 510 (1961); Tiedje, Yablonovitch et al (1984)
• Thermodynamic efficiency limit is ~33%. Si and GaAs have optimal band gaps.• Beyond Shockley-Queisser limit? 3rd-generation concepts (very hard),
multijunction structures, concentration
Main photovoltaic technologiesSilicon (wafer-based)
photovoltaicsConcentration photovoltaics
Organic photovoltaics
Mono- and poly c-Si: ∼94% of global
photovoltaic market
Efficiency record: 26.7%
Multijunctions of III-V semiconductors:
satellites, solar fields
Efficiency record: 46% (4J, ~500 suns)
Dye-sensitized solar cells, polymeric (BHJ),
fluorescent concentrators
Low efficiencies (<10%) building-integrated PV
Light trapping in silicon photovoltaic cells
Goals: - to study the effects of light trapping in c-Si photovoltaic cells - to determine the ultimate efficiency limits and the optimal design
Light harvesting…
Light harvesting + electronic transport
• Optical calculation yields spatial profile of photogenerated carriers
• Electronic transport is treated by solving drift-diffusion equations with generation and recombination terms
• Generation rate profile for a Lambertian scatterer is calculated analytically and it is isotropic ⇒ 1D electronic simulations
Efficiency limits and optimal thickness of Si solar cells: effect of impurity recombination
1 10 1002021222324252627282930
0.2 mm
0.5 mm
1 mm
4 mm2 mm
Effic
ienc
y η
(%)
Thickness (µm)
Ldiff=infty
Maximum efficiency is ∼29%. The optimal thickness is reduced from ∼80 to 20 µm when the efficiency decreases from 29% to <23%
Theoretical treatment of transport in PV cells
Drift-diffusion equations:hh
ee
RGtp
RGtn
−=⋅∇+∂∂
−=⋅∇+∂∂
J
J
Currents (number and charge): hhhhh
eeeee,,
JjEJJjEJ
epDpenDn
+=∇−=−=∇−−=
µµ
Einstein relations: TkeD
TkeD
BBh
he
e , == µµ
Poisson equation: φε
φ −∇=+−−−=∇ E),(2ad NNpne
Boundary condition at surface for minority carriers:
)()(
0h0|h
0e0|eppSJnnSJ
xx
−=−=
=
= J
0 x
Photogeneration rate: calculated from
Maxwell equations
Beyond SQ limit: perovskite-silicon tandems
P. Kowalczewski et al., J. Opt. 18, 054001 (2016)
Perovskite (ABX3) structure with Methylammonium lead iodide: CH3NH3PbI3
Tandem solar cells on silicon are a promising approach to overcome the Shockley-Quessier limit for single-junction solar cells
Nanostructured antireflection coatings for multijunction solar cells
In collaboration with RSE SpA
1 µm
Moth-Eye Antireflection Coating:ACS Appl. Mat. Interf 2014, 6, 5827
⇒ reduce reflection losses, increase the efficiency by developing broadband, omnidirectional antireflection coatings.
Final goal: improve efficiency record for MJ solar cells (now 46% 50%...)
Thermophotovoltaics: exploiting thermal radiation for cogeneration of heat and electricity
A fuel (prophane or methane) is burned in a furnace,heating a ceramic element, which emits intense infraredradiation. A photovoltaic array surrounding this emitterconverts this IR energy into electric power.
Lewis M. Fraas, Low-Cost Solar Electric Power (Springer, 2014)
Combines physics of thermal radiation and heat exchange with photovoltaics (photonics + semiconductors) ⇒ prospects for micro-cogeneration technology
Silicon photonics and optical communication
Participants: D. Gerace, M. Passoni, L. Carroll, A. Bozzola…
EU FP7 STREP project 2011-2015 FABULOUS - "FDMA Access By Using Low-cost Optical Network Units in Silicon Photonics"
EU Horizon 2020 STREP project 2016-2018 COSMICC - " CmOs Solutions for Mid-board Integrated transceivers with breakthrough Connectivity at ultra-low Cost".
Information & Communication Technologies (ICT)
Short distance: treatment of information by electrical signals on a silicon chip integrated circuit
Long distance: transmission of information by optical signals propagating in silica fibers optical fiber
Integrating electrical with optical functions on a Si chip Silicon photonics
Main component: Si strip waveguide on SiO2
Si
SiO2
Light propagation by total internal reflection
Compatible with CMOS technology electrical and optical integration
on the same chip
Si photonics chip
Image from IBM Zürich
The FABULOUS project
Project goal: to realize an optical modem (optical network unit, ONU) integrated on a silicon chip
http://www.fabulous-project.eu/
UNIPV: Physics + DIII (Electrical Engineering)
Our goal: to design a grating coupler for coupling light from an optical fiber to a silicon waveguide, using photonic crystal concepts
The COSMICC project
Project goal: to realize an optical transceiver integrated on a silicon chip
http://www.h2020-cosmicc.com/
UNIPV: Physics + DIII (Electrical Engineering)
Our goal: to develop a silicon waveguide with slow light in order to reduce energy dissipation in the Mach-Zehnder modulator
Optical modulation by electrical signal (phase shifter)
Photonic band gap and band-edge slow light in silicon grating waveguides
Periodic variation of dielectric profile along the waveguide (1D photonic crystal) photonic band gap group velocity vg=dω/dk0 at the band edge
higher interaction in phase shifter reduced dissipation in MZ modulator
⇒ band-edge slow light
M. Passoni et al., Optics Express 26, 8470 (2018)
A major application of silicon photonics: energy consumption in data centers
More than 3% of electrical energy consumption in the world (and 2% of CO2 emission) is due to data centers. This number grows rapidly. Replacing optical fiber cables with interconnections on a silicon chip would lead to major energy savings.
1 google search = 0.3 Wh = a 60 W light bulb x 17 s 0.2 g of CO2 emission
PublicationsSolar cells: A. Bozzola et al., Opt. Expr. 20, A224 (2012); Prog. Photov. 22, 1237 (2014)P. Kowalczewski et al., Opt. Lett. 37, 4868 (2012); Opt. Expr. 21, A808 (2013)A. Bozzola et al. J. Appl. Phys. 115, 094501 (2014); 117, 026102 (2015)P. Kowalczewski et al., J. Appl. Phys. 115, 194504 (2014)S. Flores Daorta et al., Appl. Phys. Lett. 104, 153901 (2014)L.C. Andreani et al., Solar Energy Mat. & Solar Cells 135, 78 (2015) P. Kowalczewski et al., Solar Energy Mat. & Solar Cells 143, 260 (2015) A. Bozzola et al., Advanced Optical Materials 4, 147-155 (2016)P. Kowalczewski et al., J. Opt. 18, 054001 (2016)C Mennucci et al., Nanotechnology 29, 355301 (2018) Two patents with with ENI: MI2013A001062 (2013), MI2015A000091 (2015)
Silicon photonics: L. Carroll et al, Optics Express 21, 21556 (2013); 22, 14769 (2014)A. Bozzola et al., Optics Express 23, 16289 (2015)M. Passoni et al., APL 110, 041107 (2017); Opt. Express 26, 8470 (2018).
Summary
The energy transition to a sustainable society will require strong effortsto boost energy efficiency and renewables (solar PV and wind+ storage, electrification, grid infrastructure, … ). Very hard job.
Solar PV market is dominated by silicon solar cells, which are reachingthe conversion efficiency limits (∼29%). Further improving the efficiencywill require developing tandem/multijunction structures.
Silicon photonics may provide a breakthrough in optical communicationvia high-speed, low-cost, low-consumption devices.
Applied research is strongly linked to basic physics research on semiconductors and photonics: radiation-matter interaction, transport, nanophotonics, photonic crystals…