Effect of p-type transition metal dichalcogenide molybdenum ditelluride (p-MoTe2) layer formation in Cadmium Telluride solar cells from numerical analysis
In this paper, we have investigated the effects of transition metal dichalcogenide namely Molybdenum ditelluride (MoTe2) layer formation in between Cadmium Telluride (CdTe) absorber layer and Mo back contact from numerical modeling. The main purpose was to investigate the possible effects of p-type MoTe2 in CdTe thin film solar cell. Energy band line-up in the vicinity of Mo/MoTe2/CdTe interface is investigated to explain the interface properties in terms of various parameters. It was found that p-type MoTe2 has some effects to the performance of CdTe thin film solar cells. Thickness, bandgap energy and carrier concentration of p-MoTe2 all have been varied in the numerical simulation to observe its effects on the cell performance. It was found that when thickness of MoTe2 is less than 20 nm, the cell efficiency decreases, which may be due to the shunting caused by the thinner p-MoTe2. Furthermore, the increase in MoTe2 bandgap results in unfavorable effect to the performance of the cell mainly due to the possibility of electrons to drift towards the back contact and recombination. The increase of the carrier concentration improves the cell performance. This could be attributed to the less recombination of electrons as well as less built in potential (Vbi) at MoTe2/CdTe junction.
Influence of the stoichiometry deviation on the electrical properties of MoTe2-x
Transport coefficient measurements (electrical conductivity, Hall effect, thermoelectric power) have been performed on single crystals of MoTe 2−x (x=0.01 and 0.015) in a wide range of temperatures. The samples were prepared by a based Te flux method and the deviation from stoichiometry was obtained by a thermal treatment. Experimental results are interpreted on the basis of a compensated p-type semiconductor model. The lacunar origin of the two impurity levels in clearly shown. For a weak departure from stoichiometry, the carriers are scattered in two ways: ionized impurities and thermal lattice modes. For a larger departure, the donor and acceptor levels broaden in two narrow energy bands. At low temperatures, the conduction mechanisms are mainly governed by a thermal hopping of small polarons in these bands. At higher temperatures, the contribution of the extended states must be taken into account. It is shown that he presence of Te-lacunar-sites leads to a greater polarization of the material and a much higher interaction between the valence and the acceptor energy bands. The model adopted here is in agreement with the band structure of the group VI transition metal dichalcogenides wich have a trigon Mesures de conductivite electrique, effet Hall et pouvoir thermoelectrique sur des monocristaux de MoTe 2−x (x=0,01 a 0,015) entre 77 et 700 K. Interpretation a l'aide d'un modele de semiconducteur de type p condense, l'origine lacunaire des deux niveaux d'impurete etant clairement mis en evidence. Pour les faibles ecarts a la stœchiometrie, diffusion des porteurs de charge par des impuretes ionisees et des modes de reseau thermiques; pour de plus grands ecarts, elargissement des niveaux donneurs et accepteurs en deux bandes d'energie etroites. A basse temperature, observation d'une conduction par sauts actives thermiquement de petits polarons dans ces bandes et, a plus haute temperature, d'une contribution des etats etendus
Changes in Quartz During Heating and the Possible Effects on Si Production
In Si and FeSi production, the main Si source is SiO2, in the form of quartz. Reactions with SiO2 generate SiO gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO2 modifications with cristobalite as the stable high-temperature phase. Transformation to cristobalite is a slow process. Its rate has been investigated for several industrial quartz sources and has been shown to vary considerably among the different quartz types. Other differences in behavior during heating between these quartz sources, such as softening temperature and volume expansion, have also been studied. The quartz-cristobalite ratio will affect the rate of reactions involving SiO2. The industrial consequences and other implications of the observed difference between quartz types are discussed. Initial studies of industrial quartz were published by Ringdalen et al. In the current work, a new experimental method has been developed, and an investigation of several new quartz sources has confirmed the earlier observed large variation between different sources. The repeatability of the data has been studied and the effect of gas atmosphere investigated. The results from the earlier work are included as a basis for the discussion.