Characterization of Thin Films for Solar Cells and Photodetectors and Possibilities for Improvement of Solar Cells Characteristics

Abstract

Faced with an alarming increase of energy consumption on one side, and very limiting amounts of available conventional energy sources on the other, scientists have turned to the most promising, renewable energy sources. Possibilities for the application of solar systems based on photovoltaic conversion of solar energy are very wide, primarily because of their relatively low cost and very important fact that solar energy is most acceptable source of electrical energy from the environmental point of view. Recently, increased investments in the development of PV technology are observed worldwide. Photovoltaic (PV) conversion of solar energy is one of the most up-to-date semiconductor technologies that enables application of PV systems for various purposes. The wider substitution of conventional energies by solar energy lies in the rate of developing solar cell technology. Silicon is still the mostly used element for solar cell production, so efforts are directed to the improvement of physical properties of silicon structures. Silicon solar cells belong to a wide group of semiconductor detector devises, though somewhat specific in its design (larger than most of the detectors). Basic part of solar cell is p-n junction, which active part is less that 0.2μm thick, so it could be treated as thin film. This photosensitive layer have the most important influence on solar cell functioning, primarily on creation of electron-hole pairs under solar irradiation, transport properties in cells, formation of internal field, and finally, output characteristics of the device such as short circuit current, open circuit voltage and efficiency. Furthermore, in order to function as a voltage generator with the best possible performances, beside p-n junction other thin films such as contact, antireflective, protective (oxide) thin films must be applied both on the front and on the back surface of solar cells. Also, in order to improve characteristics of the device, MIS structure (thin oxide layers) and back surface field layers are routinely used. Since thin films are very important in many fields of modern science (solar cell technology, for example), a large number of methods were developed for their characterization. Characterization of thin films includes investigations of physical processes in them, developing of the methods for measuring major physical and electrical properties and their