Photovoltaics: What material is best for your needs Benjamin Glassy Mark Ziffer 6/6/2013

Photovoltaics: What material is best for

your needsBenjamin Glassy

Mark Ziffer6/6/2013

Review of Current-Voltage Relationship in p-n Junction Diode

Reverse saturation current from drift:

Ideal diode equation:

Current-Voltage Relationship in p-n Junction Diode Under Illumination

• Illuminate junction by photons and create e--h+ pairs at rate = G (cm-3*s-3)• Number of holes created per second within diffusion length on n-side = ALhG• Number of electrons created per second within diffusion length on p-side = ALeG

Equation for p-n diode under illumination:

Carrier flow creates potential = Voc

Bhattacharya, Pallab. Semiconductor Optoelectronic Devices. Upper Saddle River, NJ: Prentice Hall, 1997.

At I=0, V=Voc

In organic heterojunction solar cells, photocurrent still generated at interfacial region. However, kinetic processes are very different. Hence, the need for a new ideal diode equation.

Brabec, C. J., Sariciftci, N. S. and Hummelen, J. C. Adv. Funct. Mater., 2001, 11, 15–26

Giebink, N. C., Wiederrecht, G. P., Wasielewski, M. R. & Forrest, S. R. Physical Review B, 2010, 82, 155305

1. Exciton generation in polymer (donor) and diffusion to the interfacial region

2. Charge transfer (CT) state at the interface forming polaron pair (PP) 3. New kinetic processes:

- PP can recombine to ground state: “Geminate recombination” (kPPr)- PP can separate to form free charges

4. Kinetic process:- Free charges can reform PP: “Bi-molecular recombination” (krecnIpI)


Halls, Jonathan J. M., and Richard H. Friend. "Chapter 9: Organic Photovoltaic Devices." Clean Electricity from Photovoltaics. Ed. Mary D. Archer and Robert Hill. London: Imperial College, 2001. 377-445.

Steady State Polaron Pair Recombination Rate:

Steady State Free Carrier Recombination Rate:

Jx = exciton diffusion rate at interface

ζ = polaron pair density

ζeq =equilibrium PP population

nIpI = Free electron density * free hole density

Lots of Equations


Brabec, C. J., Sariciftci, N. S. and Hummelen, J. C. Adv. Funct. Mater., 2001, 11, 15–26 Deibel, C. & Dyakonov, V. Polymer–fullerene bulk

heterojunction solar cells. Reports on Progress in Physics, 2010, 73

• Servaites, J. D., Ratner, M. A. & Marks, T. J. Organic solar cells: A new look at traditional models. Energy & Environmental Science 4, (2011)

• Giebink, N. C., Wiederrecht, G. P., Wasielewski, M. R. & Forrest, S. R. Ideal diode equation for organic heterojunctions. I. Derivation and application. Physical Review B 82, (2010) • Brabec, C. J., Sariciftci, N. S. and Hummelen, J. C., Plastic Solar Cells.

Adv. Funct. Mater., 11: 15–26, (2001)

Good References

Sticking with what you know

• Decades of silicon research for electronics applications

Awesome Solar News

• A solar-powered plane aiming to cross the US from the West Coast to East Coast has completed its third leg (landed in St Louis)• Planning around-the-world flight in 2015

Single crystal silicon from SunPower

Solarimpulse.com

Multijunction Solar Cells

Current record efficiency is held by the National Renewable Energy Lab for the cell shown at the left

These cells are very expensive to make. The main user of these high efficiency cells is NASA—weight and efficiency outweigh cost when sending things into space.

www.nrl.navy.mil

Large-scale use

• Even commercial silicon cells require 2-3 years of use before they have saved any money.

• These kinds of figures for the more exotic device architectures and materials have a much longer period.

• What if the focus was on materials that made ok solar cells, but were super cheap.

Cost benefit analysis

• 23 semiconductor materials• Assumed single junction devices• Designed devices to achieve a single pass absorption of 85%

Wadia, Cyrus; Alivisatos, A. Paul; Kammen, Daniel M. Environ. Sci. Technol. 2009, 43, 2072-2077

Figures of Merit

𝛽=𝑑∗𝑡

Minimum material intensity: β

𝐼𝐼 𝑜

=∫

280𝑛𝑚

λ 𝑏𝑔

( λ )𝑑 λ− 𝐼𝑜 ( λ )𝑒−𝛼 ( λ ) 𝑡 𝑑 λ

∫280𝑛𝑚

λ𝑏𝑔

𝐼 𝑜 ( λ )𝑑 λ=0.85

: wavelength-specific intensity of the AM1.5G solar spectrum

Power Conversion Efficiency: η

PCE was taken to be 100% of the single junction thermodynamic limit based upon Eg


Total Electricity Potential Calculation

• Annual electricity potential (TWh)𝑃=

𝐼 ∙ η ∙ 𝐴 ∙𝐶 ∙𝐻𝛽×1012

𝐼 :1000𝑊𝑚2

A: annual production per mineral in metric tons

C: capacity factor set at 0.2

H: number of hours per year

β: metric tons per year



Cost Modeling

• Note: Does not take into account cost of processing material, only extraction• Not enough data on more exotic materials investigated• For materials with this data the ratio (Cp/Ce) is highly

uniform

𝐶= 𝛽η∙ 𝐼 ∑𝑛=1

𝑥

𝐶𝑛 [ (𝑥 𝑛) (𝑀𝑛)

∑𝑚=1

𝑥

(𝑥𝑚 ) (𝑀𝑚 ) ]

𝑥𝑛𝑎𝑛𝑑 𝑥𝑚𝑎𝑟𝑒𝑎𝑟𝑒 h𝑡 𝑒𝑚𝑜𝑙𝑎𝑟 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑖𝑒𝑠𝑜𝑓 𝑎𝑛𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝑠𝑝𝑒𝑐𝑖𝑒𝑠𝑀𝑛𝑎𝑛𝑑𝑀𝑚𝑎𝑟𝑒 h𝑡 𝑒𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟𝑚𝑎𝑠𝑠𝑒𝑠𝑜𝑓 h𝑡 𝑒 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠𝑝𝑒𝑐𝑖𝑒𝑠




Plastics?

• Necessary for niche application such as flexible solar cells• Possible benefits• Cheaper manufacturing• Solution processable• Very earth abundant

• Pitfalls• Efficiencies• Lifetime

Kalowekamo, Joseph; Baker, Erin Solar Energy 2009, 83, 1224-1231

Cost of module comparison

Actual cost is not the issue….. Lifetime of the product is

Based on this research, the largest benefit would come from increasing lifetime dramatically from 5 to 10 or 15 yearsCould become competitive with inorganic PV

Kalowekamo, Joseph; Baker, Erin Solar Energy 2009, 83, 1224-1231

What to consider

• Cost versus application• Equipment availability• Possibly subsidy from the government?

Any Questions???

VBI in an Organic Diode

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Photovoltaics: What material is best for your needs Benjamin Glassy Mark Ziffer 6/6/2013