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DFT and kp modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells

  1. Top of page
  2. DFT and kp modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells
  3. Towards high efficiency segmented thermoelectric unicouples
  4. Development of gallium oxide power devices

Jacky Even, Laurent Pedesseau, Jean-Marc Jancu, and Claudine Katan

The room temperature optical absorption of 3D hybrid organic perovskites is associated to excitonic transitions between the spin-orbit split-off conduction band and the valence band. Spin-orbit coupling is about three times smaller for tin compounds. Tetragonal distortions are analysed by a kp perturbation, including spin-orbit effect. In addition, non-centrosymmetric high temperature phases exhibit a splitting of the electronic bands away from the critical point.

Phys. Status Solidi RRL (2013) DOI 10.1002∕pssr.201308183.

pssa201370079-gra-0001

Towards high efficiency segmented thermoelectric unicouples

  1. Top of page
  2. DFT and kp modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells
  3. Towards high efficiency segmented thermoelectric unicouples
  4. Development of gallium oxide power devices

Pham Hoang Ngan, Dennis Valbjørn Christensen, Gerald Jeffrey Snyder, Le Thanh Hung, Søren Linderoth, Ngo Van Nong, and Nini Pryds

Thermoelectricity, a process of converting heat into electricity and vice versa, is important for its high potential for many applications. Both the conversion efficiency and working temperature range can be greatly improved by segmenting multiple materials. Here, the authors design high-efficient thermoelectric (TE) generators by segmenting today's state-of-the-art TE materials. Their efficiencies are calculated at temperature spans of up to 1100 K, and the criterion for selecting compatible materials for segmentation is given.

Phys. Status Solidi A (2013) DOI 10.1002∕pssa.201330155.

pssa201370079-gra-0002

Development of gallium oxide power devices

  1. Top of page
  2. DFT and kp modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells
  3. Towards high efficiency segmented thermoelectric unicouples
  4. Development of gallium oxide power devices

Masataka Higashiwaki, Kohei Sasaki, Akito Kuramata, Takekazu Masui, and Shigenobu Yamakoshi

Gallium oxide (Ga2O3) is a strong contender for power electronic devices. The material possesses excellent properties such as a large bandgap of 4.7–4.9 eV for a high breakdown field of 8 MV/cm. The authors fabricated Ga2O3 metal-semiconductor field-effect transistors (MESFETs) and Schottky barrier diodes (SBDs) from single-crystal Ga2O3 substrates and MBE-grown epitaxial wafers. The MESFETs delivered excellent device performance including an off-state breakdown voltage of over 250 V, a low leakage current of only few mA/mm, and a high drain current on/off ratio of about four orders of magnitude. The SBDs also showed good characteristics such as near-unity ideality factors and high reverse breakdown voltage. These results indicate that Ga2O3 can potentially meet or even exceed the performance of Si and typical wide-gap semiconductors such as SiC or GaN for ultrahigh-voltage power switching applications.

Phys. Status Solidi A (2013) DOI 10.1002∕pssa.201330197.

pssa201370079-gra-0003