mgr inż. Aleksander Urbaniak
Metastabilne rozkłady defektów w materiałach fotowoltaicznych Cu(In,Ga)Se2
promotor: prof. dr hab. Małgorzata IGALSON
The work concerns the physics of metastable phenomena in solar cells based on Cu(In,Ga)Se2 ternary compound. The aim of this study was to verify the available theoretical predictions relating to the Cu(In,Ga)Se2, in particular to, described in the literature, metastable defects in Cu(In,Ga)Se2 and experimental verification of the mechanisms leading to the formation of metastable defect distributions in CIGS cells. Experiments were carried out using the electrical and optical methods of semiconductor characterization.
The obtained experimental results of work allowed to link metastabilities in CIGS cells with the properties of the complex vacancies VSe-VCu. In particular, the energies of creation and relaxation of metastability were calculated, showing good agreement with theoretical predictions of the complex model VSe-VCu. Based on defect prosperities explanation of metastable changes on space charge distributions have been proposed and assessed to changes of Vse-Vcu divacancy defect configurations, depending on Fermi quasi-level position in the junction. Apart from that, the non-exponential kinetics of proceses, which lead to creation, and relaxation of metastabilities and time dependence of relaxation decays on bias/light pulse duration has been linked to the model of defect conversion in configurational space. The hypothesis that those features may come from energy distribution of barrier for defect conversion as also from non-uniform availability of free carriers in the junction has been proposed. Subbandgap signal observed in photocapacitance and photocurrent spectra was interpreted in light of VSe-VCu properties. In addition, the mechanism, which may leads to metastable changes in photocapacitance and photocurrent spectra’s.
Using positron annihilation measurements, the preliminary results confirming existence of selenium and copper vacancies have been obtained and linked to the conductivity of the material. The work can be treated as a step forward in understanding of processes taking place in CIGS devices. The most important result of this work is explanation of many, up to now treated as independent, experimental facts with one model, based on properties of one defect.
mgr inż. Jerzy Antonowicz
Mechanisms and kinetics of nanocrystallization in Al-based metallic glasses
promotor: prof. dr hab. Rajmund BACEWICZ
The subject of the work is nanocrystallization in Al-based amorphous
alloys obtained by rapid quenching of the liquid. The investigations
were mostly focused on binary aluminium-rare earth glasses. The
experimental techniques used were: X-ray Diffraction (XRD),
simultaneous Small- and Wide-angle X-ray Scattering (SAXS/WAXS),
Transmission Electron Microscopy (TEM), Differential Scanning
Calorimetry (DSC) and X-ray Absorption Fine Structure Spectroscopy
(XAFS). The analysis of the of the XRD and SAXS/WAXS data allowed
formulating a new model of nanocrystallization process. According to
this model the nanocrystallization process is triggered by spinodal
decomposition of the amorphous phase. Nucleation of the primary fcc-Al
crystalline phase occurs preferentially inside the Al-rich amorphous
regions formed during the decomposition process. The size of the
crystalline grain is constrained by the region's size due to sluggish
RE atoms outside the region. The above model explains the XRD and
SAXS/WAXS spectra evolution as well as the TEM and DSC data.
A new method of quantitative XRD analysis of the glass crystallization
process was developed for the purpose of the work. Also a method of the
SAXS spectra treatment was proposed allowing estimation of the
crystalline volume fraction in a system where simultaneous amorphous
phase separation and crystallization takes place.
In a framework of the work an attempt was made towards explaining the
thermodynamic basis of spinodal decomposition in Al-based metallic
glasses for which the phase separation behavior is not expected. The
proposed explanation is based on the concept of Hume-Rothery and
Anderson of the miscibility gap in the systems with the tendency
towards ordering in a liquid phase. This concept was adopted for the
amorphous systems and was related to the Miracle's glass structure
model The comparison of the model with the XAFS data obtained for
Al-RE glasses was made. It was concluded that structure of
the Al-RE glasses can be accurately described by the Miracle's model.
This conclusion, together with the concept of Hume-Rothery and Anderson
allowed explaining the spinodal decomposition occurrence and
consequently the nanocrystalline microstructure formation.
mgr inż. Ryszard Sobierajski
Interaction of the free electron laser's femtosecond pulses with surfaces of solids
promotor: prof. dr hab. Rajmund BACEWICZ
concerns the damage mechanisms of solid surfaces under irradiation with
intense femtosecond pulses of the free electron laser TTF1 FEL. The
especially designed experimental station FELIS (Free Electron Laser -
Interaction with Solids) has been described. Next, damage of the
surfaces under irradiation with TTF1 FEL pulses have been presented.
The structural changes of the surface, ablation craters and ions
emission have been discussed for the following samples: monocrystals of
quartz and silica, thin layer of gold on silicon substrate and bulk
gold. Further, micro- and macroprocesses important for the interaction
of the femtosecond pulses with matter have been described.
Theoretical models of the surface damage have been proposed. The
results of simulations have been compared with the experimental data.
The conclusion is that the dominant mechanism of the surface damage is
a hydrodynamical process connected to a thermal interaction of the
radiation with matter.