Vitezslav Benda

Diagnostics of large-area solar cells by local irradiation

This paper presents a method for determining of local defects, which bring down efficiency and reliability of solar cells, using local irradiation of the surface of large-area solar cells. The method can give information about position and extent of local defects. Photovoltaic voltage generated by local irradiation is decreased in the area of local defects and so local defects can be determined.

Photovoltaic cells and modules - State of art and future trends

Photovoltaics has been recognized as a renewable energy technology that has the potential to contribute significantly to future energy supply. In the field of photovoltaics, material and solar cell and module fabrication technology seem to be the most important, because the progress expectations in photovoltaic applications necessitate a decrease of photovoltaic cell (module) cost on the level of more than 30% of todays one. The aim is to give information important for understanding basic problems of physics, construction and manufacturing photovoltaic cells and modules. Application of basic principles of photovoltaic cell physics and technology has been demonstrated on fabrication of crystalline silicon cells and modules, thin film cells and modules, and also new prospective technologies.

POWER SEMICONDUCTORS - STATE OF THE ART AND FUTURE TRENDS

The importance of effective energy conversion control, including power generation from renewable and environment-friendly energy sources, has increased due to rising energy demand. Power electronic systems for controlling and converting electrical energy have become the workhorse of modern society in many applications, both in industry and in the home. Power electronics plays a very important role in traction and can be considered as workhorse of robotics and automated manufacturing systems. Power semiconductor devices are the key electronic components used in power electronic systems. Advances in power semiconductor technology have improved the efficiency, size, weight and cost of power electronic systems. At present, IGCTs, IGBTs, and MOSFETs represent modern switching devices. Power integrated circuits (PIC) have been developed for the use of power converters for portable, automotive and aerospace applications. New materials (SiC and GaN) have been introduced for advanced applications. This paper reviews the state of these devices and elaborates on their potentials in terms of higher voltages, higher power density, and better switching performance.

Diagnostics of Homogeneity of Individual Layers of Large-Area Silicon Solar Cells Using Local Irradiation

This paper deals with the possibility of checking the recombination rate distribution over the area of power (large-area) solar cells from measured values of open circuit voltage VOC using local irradiation by monochromatic light of different wavelengths (LBIV-light beam initiated voltage). This method can provide information both about the distribution of the recombination centres in large-area solar cells and the surface recombination rate at the antireflection coating. From the VOC distribution, also position and extent of local defects can also be determined. The method can be used to investigate the influence of technology on characteristics of solar cells as an in-process checking with the aim of increasing efficiency and reliability of solar cells

Optimal resolution of LBIV/LBIC methods for diagnostics of solar cell homogeneity

Both LBIV and LBIC methods (light beam induced voltage and light beam induced current) are based on measuring either short circuit current <i>I</i> _sc or open circuit voltage <i>V</i> _oc under conditions of local illumination by monochromatic light of a proper wavelength. By positioning the illuminated spot, a map of either <i>I</i> _sc or <i>V</i> _oc can be obtained, from which it is possible to find the distribution of the recombination rate over the area of the solar cell. A map of either <i>I</i> _sc or <i>V</i> _oc , from which the distribution of recombination in individual layers of the cell structure can be found, should be measured within a relatively short time, and high resolution is desirable. This paper deals with the possibility of resolution adjustment for the LBIV method, and maps of crystalline silicon in these resolutions are presented.

A note on trap recombination in high voltage device structures

Abstract The carrier lifetime is a very important parameter influencing all important characteristics of bipolar devices both discrete and integrated structures and carrier lifetime tailoring is an important part of power semiconductor device technology. In presented paper, recombination through traps (centres with a deep energy level between edge of bandgap and Fermi level) is discussed in more details. It has been shown that some traps can considerably influence recombination rate in silicon and that at some traps a considerable temperature dependence of the centre cross-sections may be found. This is demonstrated in the case of iridium traps with a deep energy level 0.28 eV below the conduction band which capture cross-section temperature dependence has been found σ p + σ n ∝ T −6.5 . Further, the problem on low injection carrier lifetime in low-doped layers of high voltage semiconductor devices is also discussed.

A note on solar cell diagnostics using LBIC and LBIV methods

LBIC and LBIV methods are widely used for diagnosing solar cell homogeneity. This paper deals with the possibility of conducting LBIC measurements on the LBIV measuring device. These two methods are compared theoretically, and also by looking at the maps of the examined solar cells. Attention is paid to the working point of the LBIC method, which applies not only for modified LBIV devices but for all measurements of short circuit current.

Development of a Course on Photovoltaic Systems

The paper refers about problems connected with development of course on photovoltaics in the bachelor level of the study. Curricula of a course on photovoltaic systems performed at the Czech Technical University in Prague, Faculty of Electrical Engineering is presented. In the contribution is described the present state and compared with history and the project of the further development. Orientation of laboratory exercises towards applications has been supposed.

Using measurement of AC parameters for CIGS PV modules degradation studying

There are many diagnostic methods for PV modules parameters determination used. Most of them are based on measurement of static parameters, but therefore exist also measurement methods for AC parameters such a capacitance or impedance determination. In the paper is described Time Domain Reflectometry method which can be used for differentiation of PV modules with same static plate values. Different AC parameters can cause dissimilar behavior in alternating fields leading to premature degradation.

Determination of recombination centers in c-Si solar cells from dark I–V characteristics

For photovoltaic cells efficiency is the quality of material key ingredient. Impurities in this material create recombination centers which cut down the effective carrier charge lifetime. The method of dark current measurement, which is described in paper, can be used for dominant impurity determination.