Understanding the effect of chlorine-related defects on the CdTe electric properties is important both for obtaining high resistivity CdTe-based detectors and for high efficiency CdTe-based thin-film solar cells. The actual mechanism of the effect of Cl on electric properties of CdTe is not clear and different sometimes contradictory hypotheses appear. For example ClTeVCd shallow acceptor complex defect was proposed both as a reason of increased carrier concentration in CdTe thin film and also as a reason of high resistivity of CdTe:Cl thin films. In the present work we are trying to clarify the effect of Cl on CdTe electric properties and to find the reason of high resistivity of CdTe:Cl crystals using first principles calculations and defect chemistry modeling. For the first time we are trying to develop a model capable to describe experimental data on both high temperature and room temperature conductivity of CdTe:Cl.

Deposition of semiconductor films is a key process for production of thin-film solar cells, such as CdTe or CIGS cells. In order to optimize photovoltaic properties of the film a comprehensive model of the deposition process should be build, which can relate deposition conditions and film properties. We have developed a multiscale model of deposition of CdTe film in close space sublimation (CSS) process. The model is based on kinetic Monte Carlo method on the rigid lattice, in which each site can be occupied by either Cd or Te atom. The model tabulates the energy of the site as a function of its local environment. These energies were obtained from first-principles calculates and then approximated with analytical formulas. Based on determined energies of each site we performed exchange (diffusion) processes using Metropolis algorithm. In addition the model included adsorption and desorption processes of Cd and Te2 species. The results of the model show that a steady-state structure of the surface layer is formed during film growth. The model can reproduce transition from film deposition to film etching depending on external conditions. Moreover, the model can predict deposition rates for non-stoichiometric gas compositions.

The influence of hydrogen on the growth of carbon nanostructures in thermal chemical vapor deposition is studied using density functional theory calculations. It is shown that hydrogen adatoms effectively bind to edges of graphitic structures on the Ni (111) surface. This is found to result in a significant decrease of the rate of carbon attachment to the growing graphitic structures. However, it is also demonstrated that the edges of graphitic structures which are attached to steps on the Ni surface should not be hydrogenated.

Conversion efficiency of a solar energy in the electric is substantially determined not only by the total impurity concentration in solar cell element, but also by impurity chemical and physical state. Gettering processes, which are included in the technology of solar cell manufacturing, are usually used for such impurity redistribution. In order to optimize gettering processes we developed a program tool based on the fundamental physical and chemical laws. The description of physical and chemical behaviour of impurities in silicon is based both on known experimental data, and on calculations of necessary parameters by means of present-day thermodynamic and quantum-chemical methods. Developed tool helps to choose a gettering regime (a temperature profile, time, getter layer thickness) for optimization of these processes for the given initial chemical composition of the silicon wafer. Possibility of analysis of recombination activity of various types of defects in silicon on the basis of carrier lifetime criterion allows to obtain an estimation of efficiency of the gettering processes. Using this program tool we demonstrated that solar cell efficiency can be significantly increased by optimal choice of gettering conditions.

The extremely high scintillation efficiency of lutetium iodide doped by cerium is explained as a result of several factors controlling the energy transfer from the host matrix to activator, two of which are investigated in the present paper. The first one is the increase of the efficiency of energy transfer from self-trapped excitons to cerium ions in the row LuCl3-LuBr3-LuI3. The STE structure and the efficiency of STE to cerium energy transfer are verified by cluster ab initio calculations. We propose and theoretically validate the possibility of a new channel of energy transfer to excitons and directly to cerium, namely the Auger process when Lu 4f hole relaxes to the valence band hole with simultaneous creation of additional exciton or excitation of cerium. This process should be efficient in LuI3, and inefficient in LuCl3. In order to justify this channel we perform calculations of density of states using a periodic plane-wave density functional approach. The performed estimations theoretically justify the high LuI3:Ce3+ scintillator yield.