Plasmonic Photovoltaic -

Birck Nanotechnology Center

Plasmonic Photovoltaic

Justus C. Ndukaife, Arthur Teng


Solar Power

Current world consumption of electric energy is around 12–13 TW. The Earth receives more solar energy in one hour than the energy used globally in one year


Photovoltaic effect Photoelectric effect

In the photoelectric effect, electrons are emitted from solids, liquids or gases into vacuum when they absorb energy from light.

A. E. Becquerel, 1839 Albert Einstein, 1905 ( Nobel Prize in 1921)

In the photovoltaic effect, Electrons present in the valence band absorb light energy and, being excited, jump to the conduction band and become free.


The operation of a photovoltaic (PV) cell requires four basic attributes: • The absorption of light, generating electron-hole pairs in active region • The separation of charge carriers of opposite types at junction due to

junction potential • It will continue to diffuse away from the junction and can travel a distance

on average equal to the diffusion length before it recombines. • Collection of those carriers to an external circuit.

Photovoltaic Solar Cell Fundamentals


I-V Characteristics of PN Junction PV Cells


Shockley–Queisser limit

Shockley–Queisser limit 33% at 1.34eV bandgap, 1.1eV Si can achieve 29%

Assumptions for Shockley–Queisser limit : A single p–n-junction One electron–hole pair excited per incoming photon Thermal relaxation of the electron–hole pair energy in excess of the band gap Illumination with unconcentrated sunlight

1W. Shockley, W. and H. J. Queisser, “Detailed Balance Limit of Efficiency of p-n Junction Solar Cells,” J. of Appl. Phys., 32(3), 1961, pp. 510-519.


PV materials

M. A. Alam and S. Dongaonkar, What is Different about Thin-Film PV, NCN 2011


Development of Photovoltaics


1. Acceptable efficiency, but very low costs (thin-film, amorphous/polycrystalline materials, organic solar cells)

2. High-efficiency , but high-cost solar cells (high-quality crystalline materials, tandem solar cells)

3. Light Concentrator (high efficiency cells with optical concentration)

Low Cost AND High Efficiency? “To make power from photovoltaics competitive with fossil-fuel

technologies, the cost needs to be reduced by a factor of 2–5.”

Harry A. Atwater and Albert Polman, Nature Materials, VOL 9 MARCH 2010

Development strategy for future photovoltaics


Thin Film Solar Cell

Advantages: • Save material costs • Enable usage of PV materials like: amorphous Si and organic semiconductors • Significant reduction in thin-film solar-cell thickness would also allow the large-scale

use of scarce semiconductor materials such as In and Te • Suitable for industrial “roll-to-roll” production • Easily integrated to buildings

A thin-film solar cell (TFSC), is a solar cell that is made by depositing one or more thin layers (thin film) of photovoltaic material on a substrate.

Source: http://en.wikipedia.org/wiki/Thin_film_solar_cell


Light Trapping in thick Si vs thin film Si

•Thick Si solar cell

•Conventional Si solar cells, bulk crystalline Si is used in order to absorb light •In bulk Si, light trapping is typically achieved using a micron-sized pyramidal surface texturing

•4n2 rule-Eli Yablonovitch

Martin Green Group UNSW –Zhao, et al, 1998



•Absorption coefficient is smaller for long wavelength hence requires longer propagation length before being absorbed

•Thin film cannot absorb red light efficiently

•In thin film Si (only few um thick), light trapping requires alterative methods

•Texturing surface of thins films increases surface recombination

Beer–Lambert law

Light Trapping in thick Si vs thin film Si


Light Trapping with Nano-plasmonic Structures


Method 1: Metal Nanoparticle Plasmonic Solar Cell

Total scattering cross section (black lines), cross-section for light scattered into the substrate (red lines), and absorption cross-section (blue lines), all normalized to geometrical cross section, for 100 nm diameter hemispherical particles of Ag (solid lines) and Au (dashed lines)

K. R. Catchpole and A. Polman Appl. Phys. Lett. 93, 191113, 2008

MAIER, S. A. (2007). PLASMONICS: FUNDAMENTALS AND APPLICATIONS. Springer. p70


K. R. Catchpole and A. Polman Appl. Phys. Lett. 93, 191113, 2008

Plasmonic Anti-Reflection Coating

Fraction of light scattered into the substrate, for Ag particles on a 10 nm thick SiO2 underlayer on Si: a cylinder with diameter d=100 nm and height h=50 nm; a 100 nm diameter hemisphere; a 100 nm diameter sphere; and a 150 nm diameter sphere.


Method 2: Light concentration using particle plasmons

This works particularly well for small (below 50nm diameters) particles since absorption cross-section becomes much larger than scattering cross-section. NP works like optical antennas!

MAIER, S. A. (2007). PLASMONICS: FUNDAMENTALS AND APPLICATIONS. Springer. p70

P. Spinelli and A. Polman, 2012 / Vol. 20, No. S5 / OPTICS EXPRESS

This method (Ag nanoparticles) works well for organic cells but not for crystalline or amorphous Si!


Method 3: Light trapping using SPPs

Vivian E. Ferry, Luke A. Sweatlock, Domenico Pacifici, and Harry A. Atwater, NANO LETTERS 2008 Vol. 8, No. 12 4391-4397


Photon Management for High Efficiency Solar Cells: Improving efficiency beyond the SQ limit


Cost reduction target


Ultra-High Efficiency Solar Cells

• Shockely-Quisser limit: ultimate efficiency for single-junction solar cell is 33%

• Can we increase the efficiency above this limit?

Reduce Voc by 315mV

Incomplete light trapping: Loss of 100mV

Nonradiative exciton recombination (defects): 60mV

Fundamental thermodynamic losses 5-7%

A Polman, HA Atwater - Nature materials, 2012


Parabolic Light Directors

Atwater et.al, Appl. Phys. Lett. 99, 151113 (2011)


Tandem Cells

Conventional series tandem cell: •Complex and expensive epitaxial growth •Current-matching among the subcells is required •Each subcell is subject to the same light-concentration factor


Spectrum Splitting


•Semiconductors with different bandgaps convert different portions of the solar spectrum to reduce thermalization losses.

•Can be realized using epitaxial liftoff and printing techniques of the semiconductor layers, followed by printing of a micro- or nanophotonic spectrum splitting layer.

•Each semiconductor layer can be combined with parabolic reflectors, light trapping structures, to reduce entropy losses and these structures can be separately optimized for each semiconductor.


Thermodynamic Losses and Solution



Up-conversion

Van Sark, W. G., de Wild, J., Rath, J. K., Meijerink, A., & Schropp, R. E. (2013). Upconversion in solar cells. Nanoscale research letters, 8(1), 81. doi:10.1186/1556-276X-8-81

Aim: to increase efficiency by absorbing below-bandgap photons


Plasmonic Enhanced Upconversion

A. Atre, A. Etxarri, H. Alaeian, and Jennifer A Dionne1,J. Opt. 14 (2012) 024008

nanocrescent


Is Thin film Photovoltaics the answer?


Source -www.nrel.gov/pv/performance_reliability/pdfs/failure_references.pdf

Reliability is also very important!


Summary

PN junction solar cell fundamentals Thin film solar cell

Plasmonic enhanced light trapping

Photon Management

Plasmonic enhanced Upconversion

Thin film cells reliability issues

Plasmonic Photovoltaic -

Documents

Transcript of Plasmonic Photovoltaic -