Hello, we'll start today's course devoted on the physics of silicon solar cells for an Introduction to Semiconductor Physics. Now, we'll describe the solar cell operation. The aim of a solar cell consist in the conversion of solar energy into electricity. Photons are first absorbed by your solid. This energy it transfer to an electron that was initially bonded. It will then become free. In a further step, it will be possible to separate the positive or negative charges using an electrical field. Finally, the charges would be transferred to the metallic electrodes through a potential difference will appear. If the two electrodes are connected to a load circuit, power generation will take place. On at the end of the cycle, the electron recombines. In reality, the process is more complex. As a first lost of energy of part of the incident photon flux is reflected, then all the photon energy is not transmitted to the electrode. Some part is lost. This is called thermalization. This phenomenon will be addressed later in the course. Thereafter, the electron stay partial from positive charges is not perfect on some recombination takes place in the device. Finally, the contact between the solid semiconductor on the external circuit, can depart from perfect behavior, reducing using new losses. The electron recombines at the end. We have this principle of operation of a solar cell is your idea on real cases. The course outline will follow the same path from the impinging photon, to the load circuit. First, we'll treat the absorption of solar photon, and the creation of a free electron. This will lead us to studies a bunch of semiconductor. Then in the second part, we'll see how it is possible to transport those free electrons into the external circuit, avoiding recombination using an electrical device. This device characterized by the presence of an electric field is called the p-n junction. Finally, we will address the main causes of energy loss, starting from the optical loss, reflection of the incident photons, then thermalization losses which means that all the energy of the photon is not transmitted to the electron which has been excited. On then, the electrical losses due to carrier recommendations on the contact between the semiconductor on the metal. Now, from the physics point of view, we'll treat the crystalline semiconductors. Firstly, the band structure of pure semiconductor, then we'll deal with impurities in semiconductors, in particular, the kind of impurities leading to the so-called doping effect. We will then describe your p-n junction which is therefore, the basic principle of the solar cell. We'll then focus on the full operation of solar cell with a particular emphasis on the dominant crystalline silicon technology. From a general point of view, we can say that the discovery on use of semiconductors is probably the greatest scientific breakthrough of the 20th century. The main material that is used in semiconductor applications is silicon. Most generally, monocrystalline. Silicon is mainly used for technological reasons such as abundance, and performance of its relative insulator silica ease to process. The applications range from microelectronics, computers memories, to optoelectronic, through solar cells. The general characteristics of these microelectronics application as the miniaturization of electronic devices. So, the device performances are found to double approximately every two years. This is the so-called, Moore's law. Currently, microelectronics technology is based on smaller size than 100 nanometers. Then the transistor are developed in parallel, massively parallel, with very sophisticated processes such as etching on little coffee. On the ozone, larger applications have recently appeared on the market based on thin-film amorphous silicon. In particular, flat panel displays on solar cells. At this point, we can briefly recall the history of semiconductors. The first event in 1926, is the Bloch's theorem. It is understanding from quantum mechanics that the electron wave functions are delocalized in a perfect crystal. This theorem explains why the electron can be highly mobile in a crystal, which is a basis for semiconductor applications. So, the semiconductor theoretically developing a few years later. The theoretical basis, we are define in particular, the hole concept. The hole correspond to the lack of an electron. We'll treat this hole concept later in the course. The applications of semiconductor appears after the second war, 1948, by the first propulsion of a transistor is a Bell Laboratories in the United States, which is the origin of the electronic devices. The first solar cell was prepare a few years later. Then in the 60s, the appearance of the planar technology, was a great technological breakthrough. That is to say, the ability to simultaneously process a large number of transistors, typically, ten to the six, or to the seven. All these developments are related to crystalline materials, mostly silicon. But in the late 70s, early 80s, came the discovery of the doping capability of amorphous semiconductor, leading to large higher applications. Then in the 2000s, appear nanomaterials based on carbon and silicon, are nanostructure that are leading to new applications. So, in the next sequence, we'll start from the description of the band lecture of semiconductor. I thank you very much.
