Robert Macků

Detection and Localization of Defects in Monocrystalline Silicon Solar Cell

Near-surface defects in solar cell wafer have undesirable influence upon device properties, as its efficiency and lifetime. When reverse-bias voltage is applied to the wafer, a magnitude of electric signals from defects can be measured electronically, but the localization of defects is difficult using classical optical far-field methods. Therefore, the paper introduces a novel combination of electric and optical methods showing promise of being useful in detection and localization of defects with resolution of 250 nm using near-field nondestructive characterization techniques. The results of mapped topography, local surface reflection, and local light to electric energy conversion measurement in areas with small defects strongly support the development and further evaluation of the technique.

Multiscale experimental characterization of solar cell defects

The search for alternative sources of renewable energy, including novel photovoltaics structures, is one of the principal tasks of 21th century development. In the field of photovoltaics there are three generations of solar cells of different structures going from monocrystalline silicon through thin-films to hybrid and organic cells, moreover using nanostructure details. Due to the diversity of these structures, their complex study requires the multiscale interpretations which common core includes an integrated approach bridging not only the length scales from macroscale to the atomistic, but also multispectral investigation under different working temperatures. The multiscale study is generally applied to theoretical aspects, but is also applied to experimental characterization. We investigate multiscale aspects of electrical, optical and thermal properties of solar cells under illumination and in dark conditions when an external bias is applied. We present the results of a research of the micron and sub-micron defects in a crystalline solar cell structure utilizing scanning probe microscopy and electric noise measurement.

Determination of Surface Roughness Parameters by Optical Profilometry and Sand Patch Test

In cases when two concrete parts are cast against in different times are not connected by dowels, main contributors to the resistance are cohesion and friction. Shear resistance of the interface is highly dependent on surface treatment and its roughness. In this paper, besides the review of available methods of surface roughness determination, the optical profilometry will be introduced and described. Optical profilometry represents non-contact and non-destructive method for characterizing surface topography. Furthermore, results obtained by abovementioned method will be compared with Sand Patch Test, in order to determine its usability and limitations.

Microscale localization and isolation of light emitting imperfections in monocrystalline silicon solar cells

An imperfections or defects may appear in fabricated monocrystalline solar cells. These microstructural imperfections could have impact on the parameters of whole solar cell. The research is divided into two parts, firstly, the detection and localization defects by using several techniques including current-voltage measurement, scanning probe microscopy (SPM), scanning electron microscope (SEM) and electroluminescence. Secondly, the defects isolation by a focused ion beam (FIB) milling and impact of a milling process on solar cells. The defect detection is realized by I-V measurement under reverse biased sample. For purpose of localization, advantage of the fact that defects or imperfections in silicon solar cells emit the visible and near infrared electroluminescence under reverse biased voltage is taken, and CCD camera measurement for macroscopic localization of these spots is applied. After rough macroscopic localization, microscopic localization by scanning probe microscopy combined with a photomultiplier (shadow mapping) is performed. Defect isolation is performed by a SEM equipped with the FIB instrument. FIB uses a beam of gallium ions which modifies crystal structure of a material and may affect parameters of solar cell. As a result, it is interesting that current in reverse biased sample with isolated defect is smaller approximately by 2 orders than current before isolation process.

Investigation of Defects at Cu(In,Ga)Se2 Flexible Solar Cells on Macroscopic and Microscopic Level and their Influence on Solar Cell Performance

This paper investigates imperfection issues of Cu (In,Ga)Se2 thin-film solar cell structures and diagnostic methods of the CIGS solar cells. Electroluminescence and thermography are used to localize defect in macroscopic scale. Microstructures found in defective solar cell area are shown using micrographs. Focused ion beam was used to demonstrate that these structures interfere each solar cell layers. It is shown that micro sized defects (voids) behave as extra-stressed conductive channels that can degrade solar cells in module.

Application of Electrical Measurements to Investigation of Solar Cell Microstructure Defects

The research is aimed to the investigation of the microstructure defects in the silicon and the thin-film CIGS solar cells. These defects have their origin mainly in the technological process of a production but they can be caused by an accidental mechanical stress during a normal operation, too. That leads to a formation of the micro-cracks and the fractures, which have a significant effect on a device efficiency and reliability. The reverse-bias conditions are usually used for the defects charac- terization purposes. The mechanical induced defects increase a reverse current which leads to a strong overheating in the local breakdowns and the surroundings areas, thus for the defects localization pur- poses an infrared imaging and an electroluminescence method is used. Beyond these commonly used methods the results from the electrical current noise fluctuations observed in a frequency domain are presented in this work. The noise fluctuations measurement is a reliable indicator of a device quality and allow us to qualify the device damage extent. Using combination of these methods it is possible to localize the particular defects, assess the degree of a damage and classify the elimination process of the particular defects.

Field Measurement of Natural Electromagnetic Emissions near the Active Tectonic and Mass-Movement Fractures in Caves

Laboratory tests on a wide range of solid materials shoved that the electromagnetic emission (EME) signals are generated during the samples mechanical stress. EME anomalies have been observed also under natural conditions in association to fracture processes, tectonic loading, stress redistribution and crack propagation prior to earthquake or in relation to deep-seated gravitational mass movements. This paper describes a first prototype of the Emission data logger, which was specially developed for the continual EME monitoring in field conditions. Our equipment has been installed and tested in Obir Caves (Austria) at an active tectonic fault. The pilot long-term EME measurement results from this location are also presented in this paper.

SEM and AFM imaging of solar cells defects

The paper deals with the successive localization and imaging of solar cell defects, going from macroscale to microscale. For the purpose of localization, the light emission from reversed bias samples is used. After rough macroscopic localization, microscopic localization by scanning probe microscopy combined with a photomultiplier (shadow mapping) is performed. The type of microscopic defects are discernable from their current-voltage plot or from noise measurements. Two specific defects, both of the avalanche type, with different voltage threshold, are presented in this paper. Current voltage plots and radiant flux versus voltage characteristics for two temperatures, topography, shadow map and corresponding SEM micrographs are shown for both samples.

Cold field emission electrode as a local probe of proximal microscopes: Investigation of defects in monocrystalline silicon solar cells

Monocrystalline silicon is still very interesting material for solar cells fabrication due to its quality and external efficiency. Nevertheless during a tailoring of eligible silicon wafers, some inhomogeneities or irregularities emerge and provide defects which give trouble to good operation of solar panels. Generally, there are two classes of defects in silicon wafer: material defects due to imperfections or irregularity in crystal structure (point, line, square or volume defects), and defects induced by wafer processing. To avoid a use of damaged cells, macroscopic and microscopic measurement techniques must be applied. In this paper we present a microscopic method combining electrical noise measurements with scanning probe localization of luminous micro-spots defects. The paper brings experimental results showing local electric and optical investigations of defects in etched monocrystalline silicon solar cells and a use of cold field emission tungsten electrode as a local probe for apertureless scanni...

Optical and electrical detection and localization of solar cell defects on microscale

Monocrystalline silicon wafer is up-to-date most used material for the fabrication of solar cells. The recent investigation shows that the quality of cells is often degraded by structural defects emerging during processing steps. Hence the paper gives first an overview of solar cell efficiency investigation on macroscale. Then a detection and microscale localization of tiny local defects in solar cell structures which evidently affect electrical and photoelectrical properties of the cells is targeted. The local defects can be classified as microfractures, precipitates and other material structure inhomogeneities. Detection and localization of the defects in the structure and the assigning of particular defects to corresponding degradation of photoelectrical parameters are key points for solar cell lifetime and efficiency improvement. Although the breakdown can be evident in current-voltage plot, the localization of defects on the sample has to be provided by microscopic investigations as well as by defects light emission measurement under electrical bias conditions. The experimental results obtained from samples where the defects were microscopically repaired by focused ion beam are presented. Electrical and photoelectrical properties of sample before and after milling processing are also discussed.