ORGANIC SOLAR CELL ( organıc PHOTOVOLTAIK CELL)

1. ORGANIC SOLAR CELL (organıc PHOTOVOLTAIK CELL) Şükran GÜR Yelda ÇİFLİK

2. Organic photovoltaic cells convert solar into electric energy is probably the most interesting research challenge nowadays. • A good efficiency of these devices has been obtained by using organic semiconductor materials. • Organic materials are abundant and easily handling • Unfortunately OPV cells efficiency is significantly lower than that of inorganic-based devices, representing a big point of weakness at the present. • OPV cells are very susceptible to oxygen and water.

3. How organic solar cells work? Semiconducting conjugated polymers are the organic materials used in OPV cells, since they possess the base property required to activate the fundamental mechanisms to transform the radiative energy of light into an electric current. When a donor (D) and an acceptor (A) material are being in contact, the result is the so-called heterojunction and this is the basis for the operation of organic solar cells.

4. Solar cells on an organic basis work on a principle that is slightly different from that of normal solar cells (how solar cells work).In this view, the donor is termed the holes transporting material and it makes contact with the anode, while the electrons transporting material is the acceptor, which is in contact with the cathode. • The creation of an exciton after the absorption of a photon is the first step. The exciton diffuses inside the material to reach the donor-acceptor interface where it will be separated. • Clearly the morphology of the D/A boundary also is of great importance. third step is the exciton split-up into free charges . • The last step, that is the transport of the free charges through the sample and their collection at the electrodesis the final step and it can be considered as central in a organic photovoltaicdevice.

5. Figure 2: Examples of materials used as donors (a) and acceptors (b).

6. These measures are taken in the form of introducing a layer interface across which the potential of the electrons increases. • When an exciton crosses this boundary layer, it breaks down into an electron on one side and a hole on the other. The resulting charge imbalance causes an electric field to form at the boundary layer, pushing electrons to one side and holes to the other. • This results in clear charge separation and a difference in potential (a voltage) between the two extremities of the cell. By connecting the two sides of the cell, the electrons flow from one side to the other; a current flows across the connecting wire.

7. Type of Organic Solar cell • Single-layercells are the simplest, comprised of one organic PV material sandwiched between to metallic conductors. They are also the least advantageous, with very low efficiency and a conspicuous inability to create an electric field powerful enough to move excited electrons through the solar cell. Inresponse, researchersdevisedthe...

8. Multi-layerorganic solar cell, whichcontainstwodifferentlayers of organic PV materialcarefullychosentomaximizetheelectrostaticforcescreatedbetweenthetwo. Thisbreaksupelectronsmoreefficiently, creating a betterworking but stillproblematic solar cell. Therefore...

9. Thedispersedhetorojunctionphotovoltaicorganic solar cellwasdeveloped. Inthistypethosetwolayers, one an electrondonor, one an electronacceptor, aremixedtogetherto form a polymer. Thisenables a moreefficient solar cellthanitspredecessors, althoughthese solar cellsstillfallpreytothecommonproblemswithorganicphotovoltaicsdescribedabove.

10. Advantanges and disadvantages Theidea of organic solar cells was first put forward in the seventies, when it was discovered that the electrical conductivity of certain organic polymers greatly increased after contaminating their molecular structure with other chemicals. • Organics are a highly diverse kind of materials; their complex molecular structure allows many modifications to increase a specific material’s viability for a certain task. • Thereareproblemsthough, thefirstonebeingefficiency. Solar cells on an organicbasishave a conversionefficiency of only 3-5%, threetofivetimeslowerthanthe 15% casuallyreachedbycrystallinesilicon solar panels. • Organics are also very flexible and can be applied to almost any surface, such as thin platic film oreven layers of paint. • Thesecond problem is theinherentsensitivity of organicstoultraviolet (UV) radiation; without a protective UV-film, theorganiclayerquicklybreaksdown.

11. Another advantage inherent to organic materials is that its almost non-reflective. Thismeansorganic solar cellsarelesssensitivetoless-then-ideal lightconditions. • A largepart of thislimitedeficiency is duetotheprinciple on whichorganic solar cellsoperate. Excitons can onlytravel 3 to 10 nanometersbeforetheelectrondropsbackintoits hole, effectivelycancelingitselfout. • Organicsare also a factor 10-20 times cheaper than the silicon used in present-day normal solar cells. Solar cells on an organic basis have a conversion efficiency of only 3-5%, three to five times lower than the 15% casually reached by crystalline • Organicsarealsohighlysensitivetooxidation, forwhich a goodprotectivecoating is yet to be invented.

12. The future of organic solar cells • Much research has recently gone into improving the lifetime of organic solar cells. • And even though many improvements have been made, lots of work needs to be done before the technology becomes commercially viable. • One thing is however certain: is organic solar cellshavethepotentialtorevolutionizethewaywesee solar power. Part of thisrevolution is duetotheenormousflexbility of organicmaterial: it not unthinkable that they might one day even be applied as a special solar paint!

13. Imagine a housethat is entirelycovered in solar paint, providing it withalltheelectricity it couldpossibleneed. • Thinkaboutclothingthatrechargesyourcell-phone, an electric car whichchargesitsownbatteryor a tentwhichpowersthecookinggear on a camping site. • As you can see, thepossiblitiesaremanyandexciting. We’lljusthavetoseeifandwhentheorganicrevolutioncomes.

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