Kamel Radia

（School of Chemistry, Beihang University, Beijing 100191, China）

Abstract：After the Second Industrial Revolution, non-renewable resources such as coal, oil and natural gas are widely used in life and production. With the social and economic development and the progress of human civilization, people’s demand for energy is also growing. At present, the main energy used by mankind basically comes from these non-renewable resources.Therefore, the development of clean, environmentally friendly, huge reserves of renewable resources is imminent. Solar energy is a very ideal clean energy, which has attracted wide attention in various fields at home and abroad.

Key words：organic solar cells; working principle; energy

1 Introduction

Compared with other energy sources, solar energy has many advantages[1,4], such as: 1, rich reserves, solar energy is an inexhaustible and inexhaustible source of energy; 2,because there is no transport problem, solar energy can be used in remote mountainous or island etc.; 3, can be stored and used locally, there is light in the solar energy there. 4,environment-friendly energy, the use of solar energy will not produce waste water, waste gas, waste, etc., environmentally friendly. Human use of solar energy can be divided into: light and heat conversion, photochemical energy conversion and photoelectric conversion.

Organic solar cells are organic materials as the core of the photoelectric conversion device, although its conversion efficiency is relatively low, but because of its low price, light,soft, easy to carry, etc. It has been widely studied, such as Japan, the United States, Singapore and so on. General solar cell materials have the following requirements: to make full use of solar radiation; have a high photoelectric conversion efficiency; material itself does not cause pollution to the environment; materials for industrial production and material properties and stability. But also from the raw material resources, production technology and performance stability and other aspects of comprehensive consideration. Improve the performance of solar cells, reduce manufacturing costs and reduce the impact of mass production on the environment is the future development of solar cells the main direction.Relatively non-polar solar cells, organic solar cells with a wide range of materials, light weight, low manufacturing costs, flexibility and can be a large area of film and many other advantages. After two decades of rapid development,the photovoltaic performance of organic solar cells has made great strides, and its energy conversion efficiency has exceeded 13%, which has great potential for commercial applications in the future.

2 The classification of organic solar cells

（1）Single-junction structure of organic solar cells

There is only one material in the active layer of the single junction organic solar cell, and its cell structure is glass / metal electrode / dye / metal electrode. Its working principle is: the difference between the work function of two electrodes or the Schottky barrier formed by the contact of metal with organic material to generate the internal electric field. Electrons are extracted by a lower work function electrode, and holes are filled with electrons from a higher work function, forming a photocurrent under illumination.However, due to the rather limited migration distance of excitons in organic dyes, the recombination probability is higher in the same material, so the photoelectric conversion efficiency is generally lower (generally, ＜0.01%).

（2）P-N heterojunction structure of organic solar cells

（3）P-N bulk heterojunction structure of organic solar cells

（4）Dye-sensitized solar cells

3 The working principle of organic solar cells

The working principle of organic solar cell is different from that of inorganic solar cell. Inorganic solar cell absorbs light after inorganic semiconductor material and excites electrons directly from the valence band to the conduction band to form excitons, which are bound by the ability of electrons and holes in the library to make. Inorganic materials exciton binding energy is low, below room temperature 26meV. Inorganic materials excitons get thermal energy from the environment after the dissociation of electrons and holes to form a free charge, the final electron in the built-in electric field is collected by the electrode current.

The above process can be summarized into four processes: exciton generation, exciton diffusion, exciton separation, free charge collection. Light impinges on the organic active layer to generate excitons. The excitons diffused in the organic active layer encounter the donor /acceptor interface and dissociate into free electrons and holes. The electrons are transferred into the electron at the donor / acceptor interface Receptor material minimum unoccupied track (LUMO). Subsequently, the holes located on the highest occupied molecular orbital (HOMO) of the donor material and the electrons on the acceptor material LUMO are respectively collected by the corresponding electrodes to form photovoltaic voltages on the male and female polarities. In this way, the photocurrent effect is finally achieved.

4 Conclusion

Organic solar cells can overcome some of the problems that traditional solar cells face well and complement the advantages of traditional solar cells. The combination of the two will significantly expand the practical application of solar cells, and organic solar cell materials can be easily molecularly oriented Cutting and design, its production process is simple, can produce large areas of light-weight film, with great potential and bright prospects. However,there are also many deficiencies. At present, the primary direction should be to develop new active materials that require broad spectrum absorption of sunlight. All in all, it can be predicted that organic solar cells with high efficiency,low cost and simple process are bound to be commercialized and widely used in the near future.