Robert Macku

Near-field measurement of ZnS:Mn nanocrystal and bulk thin-film electroluminescent devices.

A near‐field study of the electro‐optical phenomena and aging characteristics of nanostructured and bulk ZnS:Mn alternating‐current thin‐film electro‐optical devices is presented. ZnS:Mn nanocrystals embedded in the glass matrices as well as ZnS:Mn thin‐film phosphors contain four different concentrations of Mn (from 0.05 to 1.0 mol%). The activator impurity in the phosphor influences the spectral properties and, to a large extent, the temporal properties of optical emission and an aging process of the devices. Therefore, a local photoluminescence and electroluminescence investigation using a scanning near‐field optical microscope technique is provided and the aging characteristics of ZnS:Mn nanocrystal structure also presented.

Study of solar cells defects via noise measurement

This article deals with the application of noise measurements for the assessment of the quality of the solar cell itself and production technology alike. The main focus of this study is the random n-level (in most case just two-level) impulse noise, usually referred to as microplasma noise. This noise is a consequence of local breakdowns in micro-sized regions and brings about a reduction of lifetime or a destruction of the PN junction. The method is suitable for non-destructive testing of semiconductor devices. Here we pay attention to very large junctions of the solar cells.

Noise and optical activities of local defects in solar cells pn junctions

This paper deals with the study of monocrystalline silicon solar cells noise and optical characteristics and correlation between them with respect to solar cells diagnostic purposes. The study was focused on finding of local defects in reverse-biased solar cells pn junctions and making their characterization. The next goal was to attribute the individual founded defects behaviour to the physical mechanisms occurring in the reverse-biased pn junction.

Detection of microstructural defects in chalcopyrite Cu(In,Ga)Se2 solar cells by spectrally-filtered electroluminescence

The aim of this research is to detect and localize microstructural defects by using an electrically excited light emission from a forward/reverse-bias stressed pn-junction in thin-film Cu(In; Ga)Se2 solar cells with metal wrap through architecture. A different origin of the local light emission from intrinsic/extrinsic imperfections in these chalcopyrite-based solar cells can be distinguished by a spectrally-filtered electroluminescence mapping. After a light emission mapping and localization of the defects in a macro scale is performed a micro scale exploration of the solar cell surface by a scanning electron microscope which follows the particular defects obtained by an electroluminescence. In particular, these macroscopic/microscopic examinations are performed independently, then the searching of the corresponding defects in the micro scale is rather difficult due to a diffused light emission obtained from the macro scale localization. Some of the defects accompanied by a highly intense light emission very often lead to a strong local overheating. Therefore, the lock-in infrared thermography is also performed along with an electroluminescence mapping.

Investigation of adsorption-desorption phenomenon by using current fluctuations of amperometric NO 2 gas sensor

Nitrogen dioxide (NO2) is a highly toxic gas harmful to the environment even at low concentrations. To overcome limitations of standard solid NO2 sensors based on inorganic materials, a fully printed sensor with solid polymer electrolytes (SPE) was developed in Regional Innovation Centre for Electrical engineering in Czech Republic. The amperometric sensor is based on a semi-planar three-electrode topology (reference, working and counter electrode) and solid polymer electrolyte. This paper focuses on adsorption-desorption phenomenon by studying current fluctuations and current mean value of amperometric NO2 gas sensor during its exposition to concentration cycle. Limits of NO2 concentration are from 0 to 6 ppm. Background noise and thermal noise are only apparent for zero concentration, while, noise 1/f becomes main component of current fluctuations for higher NO2 concentrations.

Non-Destructive Characterization of Micro-Sized Defects in the Solar Cell Structure

This article discusses the issue of noise measurements application for the quality assessment of the solar cells themselves and production technology alike. The main focus of our research is the random n-level (in most case just two-level) impulse noise, usually referred to as microplasma noise. This noise was found to be in a direct consequence of local breakdowns in micro-sized regions and brings about a reduction of lifetime or a destruction of the pn junction. Non-destructive measurement methodology as presented here is suitable for testing of a large number of various semiconductor devices not only for solar cells. In this paper experimental measurement of noise signals in the frequency and time domain is presented. Furthermore the microplasma noise behaviour and defect geometry is discussed.

Light emission from silicon solar cells as characterization technique

The paper describes local photoelectric measurement results obtained with monocrystalline silicon solar cell in visible light. The measurement allows localize a weak light emission from defects at reverse bias voltage as low as 3 V, which does not exhibit any relation to current-voltage characteristics (no local breakdowns). Other types of defects observed under forward bias using electroluminescence (EL) and light induced beam current (LBIC) techniques are also visualized. The measurements should contribute to find a correlation between EL and modified LBIC results.

Narrow-band noise as a tool for diagnostics of solar cells PN junctions

Presented paper deals with noise diagnostics of defects in monocrystalline silicon solar cells PN junctions. Localized regions featuring increased concentration of donor or acceptor impurities, other element admixtures or other defects which cause the PN junction reverse breakdown voltage to be reduced. When a high electric field is applied to this PN junction, local breakdowns arise in micro-sized regions, which in turn can lead to the deterioration in quality or destruction of the PN junction. The useful tool for diagnostics of local defects in PN junctions is the reverse-biased PN junction narrow-band RMS noise current vs. reverse voltage measuring. The set of crystalline silicon solar cells with different structure was studied by this noise diagnostic method.

Diagnostics of Forward Biased Silicon Solar Cells Using Noise Spectroscopy

Our research is above all focused on non‐destructive testing of the solar cells. We study a single‐crystal silicon solar cells n+p and we don’t have serious information about features of a pn junction and impurities distribution. The main point of our study is characterization of the local defects in samples. These defects lead to live‐time reduction and degradation of reliability. Flicker noise in forward biased solar cells is subject of this paper. We will discuss our measurement with Kleinpenning approaches for inhomogeneous semiconductors and we suggest the physical nature of the samples behaviour.

Local light to electric energy conversion measurement of silicon solar cells

The paper is focused on non-destructive detection of structural errors, and on local illumination to electric energy conversion measurement in the solar cell using a near-field optical scanning microscope (SNOM). The principal objective of this study is to find out a relationship between surface or structure errors and defects observed in electric characteristics of solar cell samples. The defects and local mechanical damage of Si solar cell can result in lower light to electric energy conversion efficiency. The influence of surface scratching on reverse I-V characteristics of single-crystal silicon solar cell is also presented. The topography measurement, local surface reflection and local light to electric energy conversion measurement in areas damaged by a scratch are also provided.