Organic photovoltaic

Organic photovoltaic

1. Organic Photovoltaic

2. Introduction Through the ages mankind needed more and more energy. Oil, gas and coal will not last forever and it takes a number of years until new fossil fuels are formed. The Earth receives 174,000 (TW) of incoming solar radiation at the upper atmosphere, so as a solution the sun became an important source of renewable energy .

3. What is organic photovoltaic Organic photovoltaic cell (OPVC) or organic solar cell is a class of solar cell that uses conductive organic polymers or small organic molecules for light absorption and charge transport to produce electricity from sunlight by the photovoltaic effect. Organic photovoltaic (OPV) cell absorbing layer is based on organic semiconductors (OSC)- typically either polymers or small molecules.

4. Why organic photovoltaic cell? Organic photovoltaic (OPV) solar cells aim to provide an Earth-abundant and low-energy production photovoltaic (PV) solution.
This New technology also has the theoretical potential to provide electricity at a lower cost than the classical solar cells (inorganic PV cells).

5. Structure of organic photovoltaic cell Overall, organic cells are structured very similarly to crystalline silicon solar cells. The most notable difference between the two cell types is the semiconducting layer; instead of crystalline silicon, organic cells use carbon-based compounds (organic molecules) that are printed in an extremely thin layer onto a plastic backing. Optical photons absorbed and creates exitons (bound electron-hole pair).
The negative electrode is Aluminum.

6. Indium Tin Oxide(ITO) is the common transparent electrode.
The substrate is glass.
Current is generated when the resulting free electrons and holes are transported through the donor polymer and acceptor fullerene, respectively, to the electrodes

7. How do Organic Photovoltaic Cell Work: The purpose of an OPV is to generate electricity from sunlight. This is achieved when the energy of light is equal to or greater than the band gap, leading to absorption and excitation of an electron – from the HOMO to the LUMO
The excited electron will leave behind a positively-charged space known as a ‘hole. Due to the opposite charges of the hole and electron, they become attracted and form an electron-hole pair, also known as an ‘exciton’. To remove the charged particles from the solar cell, the electron-hole pair must be separated, and this process is known as ‘exciton dissociation’.

8. Typically in an inorganic semiconductor, the attraction between the electron and hole (known as the exciton binding energy, Eb) is small enough to be overcome by thermal energy at room temperature (approximately 26 meV).3
In contrast, OSCs have low dielectric constants, giving large Eb values in the range of 0.3-0.5eV.4 Depending on how the exciton dissociates, the OSCs are classified as either a ‘donor’ or ‘acceptor’ The donor-acceptor band gap offset typical in an OPV, used to overcome exciton binding energy and facilitate dissociation

9. The steps that govern OPV working can be summarised as: Absorption of incident, light leading to exciton generation
Diffusion of the exciton to a donor-acceptor interface Dissociation of the exciton across this interface Charge-carrier transport Charge-carrier collection

10. Types of organic photovoltaic Cell Junction types: - Single layer organic solar cell
Bilayer
Bulk heterojunction
Graded heterojunction
Continuous junction

11. Single layer organic solar cell Single layer cells are simplest.
These cells are made by sandwiching a layer of organic electronic materials between two metallic conductors. When the organic layer absorbs light, electrons will be excited to the LUMO and leaves holes in the HOMO, thereby forming excitons. Example Al/MgPc/Ag

12. Bilayer Bilayer cells contain two layers in between the conductive electrode.
The two layers have different electron affinity and ionization energies, therefore electrostatic forces are generated at the interface between the two layers., Materials carefully chosen to maximize the electrostatic force between the two.this break up electron more efficiently, create better working than single layer photovoltaic cells. This structure is also called a planar donor-acceptor heterojunction. Example C60/MEH-PPV

13. Bulk heterojunction Bulk heterojunction have an absorption layer consisting of a nanoscale blend of doner and accepter material Efficient bulk heterojunctions need to maintain large enough domain sizes to form a percolating network that allows the donor materials to reach the hole transporting electrode 1 and the acceptor materials to reach the electron transporting electrode 2 Without the percolating network, charges might be trapped in a donor or acceptor rich domain and undergo recombination. Bulk heterojunctions are most commonly created by forming a solution containing the two components, casting (e.g. Drop casting and spin coating) and then allowing the two phases to separate.

14. After the capture of a photon, electrons move to the acceptor domains, then are carried through the device and collected by one electrode, and holes move in the opposite direction and collected by one electrode, and holes move un the opposite direction and collected at the other side. Example Dye synthesized photovoltaic cell

15. Graded heterojunction: - The electron donor and acceptor are mixed in such a way that the gradient is gradual. This architecture combines the short electron travel distance in the dispersed heterojunction with the advantage of the charge gradient of the bilayer technology. Example A cell with a blend of CuPc and Co showed à quantum efficiency of 50% and a power conversion efficiency of 2.1% using 100 mW/cm² simulated AM1.5G solar illumination for a graded heterojunction.

16. Continuous junction Similar to the graded heterojunction the continuous junction concept aims at realizing a gradual transition from an electron donor to an electron acceptor. However, the acceptor material is prepared directly from the donor polymer in a post-polymerization modification step.

17. Environmental impact of organic solar cell: The use of land The use of water The use of natural resources The use of hazardous materials The life-cycle global warming emissions The visual impact

18. Applications Building integration Building-integrated photovoltaics (BIPV) is a key example of an application of solar cells . Increasingly conventional solar cells are being incorporated into the construction of new buildings as a source of electrical power and existing buildings are retrofitted with solar cell technology. E.g  solar charging station

19. Power generation Power generation is the point of solar cells and with these application pages we wish to demonstrate examples of organic solar cells being used for larger scale power generation while the key benefits of organic solar cells are preserved (read: flexibility, lightness, etc.). E.g E bike charger

20. Gadegts Incorporating organic solar cells into consumer products (gadgets) allows for a design freedom not possible with conventional solar cell technologies. E.g HeLi -on - the pocketable solar panel

21. Advantages and disadvantages of organic photovoltaic cells: Advantages of organic photovoltaic cells: Environmental Sustainability : Photovoltaic cells generate clean and green energy as no harmful gases such as Co2, NO2 etc are emitted. Also noise pollution which makes them ideal for application in residential areas. Economically Viable : Operation and maintenance cost of cells are very low. Accessible : Solar panels are easy to set up and can be made accessible. Renewable : Energy is free and abundant in nature. Cost Solar panels have no mechanically moving parts, the solar panel price for maintenance and repair is negligible.

22. Disadvantages of Photovoltaic Cells: Low efficiency Power generated gets reduced during cloudy weather. Long-range transmission of solar energy is inefficient and difficult to carry. Photovoltaic panels are fragile and can be damaged relatively easily
Current produced is DC in nature conversion of DC current to AC current involves the use of additional equipment such as inverters.

23. ORGANIC SOLAR CELLS VS INORGANIC SOLAR CELLS EFFICIENCY: Organic solar panels could give 11% to 12%. While inorganic solar panels offer you 20+% efficiency. MATERIALS: The major difference between organic and inorganic solar cells is of the semiconductor. Inorganic solar cells have crystalline silicon. On the other hand, inorganic solar cells have carbon-based organic compounds PRICE: organic solar cells are not available for commercial and residential uses, so comparing it to inorganic solar cells does not make sense.

24. References https://easysolar.guide/organic-solar-cells-vs-inorganic-solar-cells/ https://www.ossila.com/pages/organic-photovoltaics-introduction https://www.ossila.com/pages/organic-photovoltaics-introduction https://www.google.com/amp/s/vdocuments.mx/amp/differantes-types-of-organic-solar cells-and-applications.html