Organic Solar Cells - Jacobs University Bremen fileIntroduction Physics of Organic Solar Cells Research Prospects Reference Solar Cells Organic Solar Cells History of Solar Cell Started

IntroductionPhysics of Organic Solar Cells

Research ProspectsReference

Organic Solar Cells

Rahul Dewan

Organic Electronics Course PresentationInternational University Bremen

4th May 2006

Rahul Dewan Organic Solar Cells



Outline

1 IntroductionSolar CellsOrganic Solar Cells

2 Physics of Organic Solar CellsStructureWorking principle

3 Research ProspectsComparisonImproving efficiency

4 Reference




Solar CellsOrganic Solar Cells

History of Solar Cell

Started with French scientist Edmond Becquerel’s photoelectric experiments in1839.

First solar cell using junctions was built by an American, Charles Fritts in 1883. (Itwas formed using coated selenium and gold, as a result, efficiency of only 1%)

Albert Einstein publishes his paper on the photoelectric effect in 1905 for which helater receives the nobel prize.

Energy efficient silicon solar cell finally built in 1941 by Russell Ohl.

In the USA, Daryl Chapin, Calvin Fuller and Gerald Pearson develop the siliconphotovolatic(PV) cell at Bell Labs in 1954. It was the first solar cell capable ofconverting enough of the sun’s into power to run everyday electrical equipments.













































Schematics of p-n junction Solar Cell





Operation of p-n junction Solar Cell

The I-V characteristic of such a device is given by

I = Is“

eqV/kT − 1”− IL (1)





Operation of p-n junction Solar Cell





Equations related to Solar Cell

From equation (1), when I = 0, we obtain the open circuit voltage, VOC

VOC =kT

qln

„ILIS

+ 1«∼=

kT

qln

„ILIS

«(2)

The maximum output power Pm is,

Pm = ImVm ∼= IL

»VOC −

kT

qln

„1 +

qVm

kT

«−

kT

q

–(3)

Fill factor FF is given by,

FF =ImVm

ILVOC(4)

And, the power conversion efficiency η

η =FF .ILVOC

Pin(5)





Why Organic Solar Cells ?

The discovery of metal-like electrical conductivity of polyacetylene in 1976 byShirakawa with Heeger and MacDiarmid opened the field of research of polymers.

Avdantages of organic solar cells !

Relatively cheap in production and purification.

Materials can be tailored for the demand.

Can be used on flexible substrate.

Can be shaped or tinted to suit architectural applications.

Disadvantages of solar cells!

Do not reach the energy conversion efficiency exceeding 24 % in inorganicmaterials.

Limited lifetime/ stability issue.




















































































































StructureWorking principle

Types of organic solar cells

There are 3 types of organic solar cells.1 Dye sentisized nanocrystalline TiO2 solar cells.2 Molecular organic solar cells.3 Polymer solar cells.[Meissner, 1999]

Attracting great interest as photovolatic materials.Breakthrough came with the introduction of the bulk heterojunction.


























Device structure

ITO Indium Tin OxidePEDOT:PSS Poly (ethylene-dioxythiophene) doped

with polystyrenesulphonic acidMMDO-PPV (poly-(2-methyloxy, 5-(3,7 - dimethyloctyloxy))

para phenylene-vinylene)PCBM ([6,6]-Phenyl C61 butyric acid methyl ester





Materials used





From light into electricity

In three essential steps, light energy is transformed into electricity by organic solarcells.

1 Absorption of light2 Charge carrier generation3 Transport of the opposite charges to the opposite contacts.


























Metal-insulator-metal(MIM) model

For four situations, a semiconductor, sandwiched between two metal electrodes withdifferent work functions, is depicted above.




ComparisonImproving efficiency

Performance evaluation

Type of cell Efficiency(%) Research needsCrystalline silicon 24 Higher production yields, lowering of cost

and energy contentMulticystalline silicon 18 Lower manufacturing cost and complexityAmorphous silicon 13 Lower production costs, increase

production volume and stabilityOrganic solar cells 2-3 Improve stability and efficiency





Outlook & Strategies

Device performance can be optimized by optimization of the device physics.

Optimize the choice of metallic electrodes.

Optimize the choice of donor-acceptor pair. The bandgap of the semiconductorshould be chosen for efficient harvesting of the solar spectrum.

Optimize the network morphology of the phase-separated composite material forenhanced transport and carrier generation.






















For Further Reading

M. GratzelPhotoelectrochemical cells.Nature, Vol 414, 15 November 2001.

C.J. Brabec et al.Plastic Solar Cells.Advanced Functional Materials, 2001, 11, No 1. February

C. WinderSentisization of Low Bandgap Polymer Bulk Heterojunction Solar Cells.

S.M. SzeSemiconductor Devices, Physics and Technology.

S. DimitrijevUnderstanding Semiconductor Devices.

D. Meissner.Photon 2, 34-37


Documents

Organic Solar Cells - Jacobs University Bremen fileIntroduction Physics of Organic Solar Cells Research Prospects Reference Solar Cells Organic Solar Cells History of Solar Cell Started