Thallium bromide (TlBr) is a promising semiconductor for the fabrication of radiation detectors because of its large carrier mobility and high gamma-ray stopping power. It is also known that the serious degradation of performance is often observed in TlBr-based detectors during the device operation, probably due to the carrier transport degradation caused by the appearance of some crystal defects. However, the origin of such defects is still unknown at present. In this work, we study electronic properties of defects in TlBr and clarify the origin of degradation, using the first-principles calculations.

In this work, we will develop a method to lift off CIGS solar cells from glass substrates. ZnO layer is formed as a sacrificial layer between the glass substrate and the Mo layer that is the back electrode of the CIGS solar cell. The CIGS solar cell is lifted off from the glass substrate by etching only the ZnO layer in an acetic acid. In this study, we will report that the Mo layer is lifted off from the glass substrate in acetic acid for a sample with Mo/ZnO/SLG structure and that CIGS solar cell can be deposited on this structure.

To perform the calculation of Cu(In,Ga)S₂ / Cu(In,Ga)Se₂ tandem-type solar cells, we introduced a recombination layer between the top and bottom cell. We have successfully calculated the cell performance by optimizing the recombination layer. It was found that an efficiency of 30.4% can be obtained with a bottom-cell bandgap of 1.10 eV and a top-cell bandgap of 1.71 eV.

Preparation of Cu₂Sn_1-xGe_xS₃(CTGS) thin films on Mo substrates by sol-gel sulfurization method was investigated. To prevent degradation of a Mo layer, Cu-Sn low concentration solution was coated on the Mo layer, after then Cu-Sn-Ge high concentration solution was coated. The precursor was sulfurized in H₂S (3%) + N₂ atmosphere. XRD patterns of deposited films showed a peak between Cu₂SnS₃ and Cu₂GeS₃.

Cu₂Sn_1-xSi_xS₃ (CTSiS) is a potential material for cost-effective and non-toxic absorbers in thin film solar cells. However, the basic physical properties of CTSiS have not been thoroughly investigated. Therefore, polycrystalline CTSiS with different Cu/IV ratios grew by solid-state reaction, and photoluminescence was observed. As a result of PL measurement of these samples, PL was observed at ~0.92 eV, 1.04 eV, and 1.13 eV.

Electronic and optical properties of solar-cell perovskite semiconductors such as CsPbI₃ are studies by the first-principles calculations and compared with conventional solar-cell semiconductors like GaAs. It is shown that, although the band structure is quite different between CsPbI₃ and GaAs, the photo-absorption has similar spectra in visible-light region. The reason of such similarity is analyzed based on their electronic structures.

The optical thin films have been prepared via layer-by-layer deposition of ZnS and ZnSe nanoparticles on glass substrates. The thickness and optical constants of the prepared thin films were determined by spectroscopic ellipsometry. We demonstrated the applicability of multi-layered semiconductor nanoparticles as a material for optical thin films.

The time-resolved light-induced deformation phenomena in layered TlGaSe₂ has been investigated using Sagnac interferometer. The deformation occurred repeatedly in response to pump light irradiation. We successfully observed the transient response of the deformation with pulsed laser using Sagnac interferometer.

We reported the crystal structure on surface of CZTS films using Raman spectroscopy by two-dimensional scanning. In addition, we analyzed the change in crystal structure before and after sulfur-anneal treatment to CZTS films. The result showed that Cu₂S distributed on the surface of as-deposited CZTS films was estimated to be 13.0 (um)² by high-resolution Raman mapping approaching the diffraction limit. Furthermore, it was found from the Raman mapping that the Cu₂S phase was reduced by annealing sulfur at 600 ℃.