Synthesis of alkaline-earth Zintl phosphides MZn₂P₂ (M = Ca, Sr, Ba) from Sn solutions

Exploration of suitable partner materials (so-called buffer layer or n-type emitter) for each light-absorbing material is essential to practicalize various emerging photovoltaic devices. Motivated by our recent discovery of a partner material, Mg(Mg x Zn₁−x)₂P₂, in Mg/Zn₃P₂ solar cells, the related series of materials MZn₂P₂ (M = Ca, Sr, Ba) is of interest to the application in pnictide-based solar cells. In this study, we synthesize these materials to evaluate the optoelectronic properties concerning photovoltaic applications. To deal with the difficulties of the high vapor pressure and reactivity of the constituent elements, we utilized Sn as a solvent to reduce their activities during heat treatments. Powders that are mainly composed of MZn₂P₂ were obtained by crushing the samples after solution growth, although single-phase crystals of MZn₂P₂ could not be obtained in this study. The optical bandgap and the ionization potential of each MZn₂P₂ were evaluated through the diffuse reflectance and the photoelectron yield spectroscopy measurements of the powder. As a result, we found that CaZn₂P₂ would be a promising partner material in photovoltaics based on Zn₃P₂ and ZnSnP₂

光・電子デバイスを指向した燐化亜鉛関連材料および界面の特性に関する研究

京都大学0048新制・課程博士博士(工学)甲第21104号工博第4468号新制||工||1694(附属図書館)京都大学大学院工学研究科材料工学専攻(主査)教授 杉村 博之, 教授 田中 功, 准教授 野瀬 嘉太郎学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDFA

Fabrication process and device application of chalcopyrite phosphides based on thermodynamics

In this article, we introduce our studies on the application of chalcopyrite phosphides to solar cells, including bulk crystal growth based on the phase diagram, and thin film deposition through chemical potential diagram. A phase diagram is a useful tool for the fabrication of multi-component materials, while the chemical potential diagram, which is a kind of phase diagram with chemical potentials as axes, is well suited for discussing vapor growth. As another example of using the chemical potential diagram, the stability of a hetero-interface is presented. In addition, bandgap control through order-disorder phenomena is described

Preparation of a CuGaSe2 single crystal and its photocathodic properties

Chalcopyrite CuGaSe2 single crystals were successfully synthesized by the flux method using a home-made Bridgman-type furnace. The grown crystals were nearly stoichiometric with a Se-poor composition. Although a wafer form of the thus-obtained single crystal showed poor p-type electrical properties due to such unfavorable off-stoichiometry, these properties were found to be improved by applying a post-annealing treatment under Se vapor conditions. As a result, an electrode derived from the Se-treated single crystalline wafer showed appreciable p-type photocurrents. After deposition of a CdS ultrathin layer and a nanoparticulate Pt catalyst on the surface of the electrode, appreciable photoelectrochemical H2 evolution was observed over the modified electrode under photoirradiation by simulated sunlight with application of a bias potential of 0 VRHE

Deep level transient spectroscopy and photoluminescence studies of hole and electron traps in ZnSnP₂ bulk crystals

ZnSnP₂, an emerging inorganic material for solar cells, was characterized by deep level transient spectroscopy (DLTS) and photoluminescence (PL). Acceptor- and donor-like traps with shallow energy levels were detected by DLTS analysis. The previous study based on first-principle calculation also suggested such traps were due to antisite defects of Zn and Sn. PL measurements also revealed sub-gap transitions related to these trap levels. Additionally, DLTS found a trap with a deep level in ZnSnP₂. A short lifetime of minority carrier in previous work might be due to such trap, coming from phosphorus vacancies and/or zinc interstitials suggested by the first-principle study

Machine-Learning-Based phase diagram construction for high-throughput batch experiments

To know phase diagrams is a time saving approach for developing novel materials. To efficiently construct phase diagrams, a machine learning technique was developed using uncertainty sampling, which is called as PDC (Phase Diagram Construction) package [K. Terayama et al. Phys. Rev. Mater. 3, 033802 (2019).]. In this method, the most uncertain point in the phase diagram was suggested as the next experimental condition. However, owing to recent progress in lab automation techniques and robotics, high-throughput batch experiments can be performed. To benefit from such a high-throughput nature, multiple conditions must be selected simultaneously to effectively construct a phase diagram using a machine learning technique. In this study, we consider some strategies to do so, and their performances were compared when exploring ternary isothermal sections (two-dimensional) and temperature-dependent ternary phase diagrams (three-dimensional). We show that even if the suggestions are explored several instead of one at a time, the performance did not change drastically. Thus, we conclude that PDC with multiple suggestions is suitable for high-throughput batch experiments and can be expected to play an active role in next-generation automated material development

Fabrication process and device application of chalcopyrite phosphides based on thermodynamics

In this article, we introduce our studies on the application of chalcopyrite phosphides to solar cells, including bulk crystal growth based on the phase diagram, and thin film deposition through chemical potential diagram. A phase diagram is a useful tool for the fabrication of multi-component materials, while the chemical potential diagram, which is a kind of phase diagram with chemical potentials as axes, is well suited for discussing vapor growth. As another example of using the chemical potential diagram, the stability of a hetero-interface is presented. In addition, bandgap control through order-disorder phenomena is described