Impurity-to-efficiency simulator: Predictive simulation of solar cell efficiencies based on measured metal distribution and cell processing conditions

We present a fast and simple 1D simulation tool to predict solar cell performance as a function of the initial iron content and distribution in the as-grown silicon wafer, the time-temperature profiles applied during the fabrication process, and several parameters related to cell architecture. The applied model consists of three parts that are validated by comparison to experimental results from literature. Assuming a time-temperature profile of a standard solar cell fabrication process, we calculate the redistribution of iron and the evolution of minority carrier lifetime for different as-grown Fe distributions. The solar cell performance as a function of the total iron concentration and the final lifetime distribution is also simulated and compared to experimental results for multicrystalline Si. Keywords: simulation, crystalline silicon solar cell, getterin

Hydrogen Behavior at Crystalline/amorphous Interface of Transparent Oxide Semiconductor and its Effects on Carrier Transport and Crystallization

The role of disorder and particularly of the interfacial region between crystalline and amorphous phases of indium oxide in the formation of hydrogen defects with covalent (In-OH) or ionic (In-H-In) bonding are investigated using ab initio molecular dynamics and hybrid density-functional approaches. The results reveal that disorder stabilizes In-H-In defects even in the stoichiometric amorphous oxide and also promotes the formation of deep electron traps adjacent to In-OH defects. Furthermore, below-room-temperature fluctuations help switch interfacial In-H-In into In-OH, creating a new deep state in the process. This H-defect transformation limits not only the number of free carriers but also the grain size, as observed experimentally in heavily H-doped sputtered In2Ox. On the other hand, the presence of In-OH helps break O2 defects, abundant in the disordered indium oxide, and thus contributes to faster crystallization rates. The divergent electronic properties of the ionic vs covalent H defects passivation of undercoordinated In atoms vs creation of new deep electron traps, respectively and the different behavior of the two types of H defects during crystallization suggest that the resulting macroscopic properties of H-doped indium oxide are governed by the relative concentrations of the In-H-In and In-OH defects. The microscopic understanding of the H defect formation and properties developed in this work serves as a foundation for future research efforts to find ways to control H species during deposition

Electronic Structure and Light-Induced Conductivity of a Transparent Refractory Oxide

Combined first-principles and experimental investigations reveal the underlying mechanism responsible for a drastic change of the conductivity (by 10 orders of magnitude) following hydrogen annealing and UV irradiation in a transparent oxide, 12CaO · 7Al2O3, found by Hayashi et al. [Nature (London) 419, 462 (2002).] The charge transport associated with photoexcitation of an electron from H- occurs by electron hopping.We identify the atoms participating in the hops, determine the exact paths for the carrier migration, estimate the temperature behavior of the hopping transport, and predict a way to enhance the conductivity by specific doping

Consumo de álcool e drogas: principais achados de pesquisa de âmbito nacional, Brasil 2005

OBJECTIVE: To assess alcohol and drug use in a representative sample of the urban Brazilian population and their correlation with sexual and reproductive health. METHODS: Data from a national population-based survey with a complex sampling, performed in 2005 was used. A total of 5,040 individuals from both genders, in the age group from 16 to 65 years old, were interviewed. Issues regarding drug and alcohol use and sexual behavior were assessed. Bivariate and multivariate analyses were used. RESULTS: Alcohol was the most frequently used substance, with reports of regular use in the lives of 18% of interviewees. Use of illegal drugs was mentioned by 9% of the interviewees especially marijuana and snorted cocaine; injected drugs use was not frequent. There was a decrease in snorted cocaine use and an increase in marijuana use (in the last 12 months), compared to results of a similar survey conducted in 1998. History of sexual abuse was a risk factor for drug use and regular alcohol use. Interviewees mentioning the role of religion in their background, being White, and female were less likely to use alcohol in a regular way, which is especially prevalent among elderly males.Leisure activities and absence of current religious practice were associated with drug use. CONCLUSIONS: The regular or irregular alcohol use is prevalent in the urban Brazilian population, whereas injected drug use is rare. Over the last decade there was a decline in cocaine use. A history of sexual abuse was central to later use of alcohol and drugs.OBJETIVO: Analisar os padrões de consumo de álcool e drogas de uma amostra representativa da população urbana brasileira na sua inter-relação com a saúde sexual e reprodutiva. MÉTODOS: Dados de inquérito de base populacional, de abrangência nacional, com plano amostral complexo, realizado em 2005. Foram entrevistados 5.040 indivíduos de ambos os sexos, na faixa etária de 16 a 65 anos. Analisaram-se questões relativas consumo de álcool e drogas e comportamento sexual. Utilizou-se análise bivariada e multivariada. RESULTADOS: O álcool foi a substância mais freqüentemente utilizada, com relato de uso regular, na vida, por 18% dos entrevistados. O consumo de drogas ilícitas foi referido por 9% dos entrevistados, especialmente, maconha e cocaína aspirada, com uso de drogas injetáveis infreqüente. Observou-se declínio do consumo de cocaína aspirada e incremento do uso de maconha (nos últimos 12 meses), comparados a resultados de pesquisa similar realizada em 1998. Histórico de abuso sexual constituiu fator de risco do consumo de drogas e uso regular de álcool. A referência por parte do entrevistado ao papel da religião na sua formação, ser branco e do sexo feminino se mostraram protetores frente ao consumo regular de álcool, particularmente prevalente entre homens mais velhos. As opções de lazer e a ausência de práticas religiosas atuais se mostraram associadas ao consumo de drogas. CONCLUSÕES: O consumo de álcool, regular ou não, é prevalente na população urbana brasileira, enquanto o uso de drogas injetáveis se mostrou raro. Ao longo da última década observou-se declínio no consumo de cocaína. Histórico de abuso sexual se mostrou central ao consumo posterior de drogas e álcool

Tunable Conductivity and Conduction Mechanism in a UV light activated electronic conductor

A tunable conductivity has been achieved by controllable substitution of a novel UV light activated electronic conductor. The transparent conducting oxide system H-doped Ca12-xMgxAl14O33 (x = 0; 0.1; 0.3; 0.5; 0.8; 1.0) presents a conductivity that is strongly dependent on the substitution level and temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x = 0) to 0.106 S/cm (x = 1) at room temperature. At each composition the conductivity increases (reversibly with temperature) until a decomposition temperature is reached; above this value, the conductivity drops dramatically due to hydrogen recombination and loss. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Mg-substituted system with x=0, 1 and 2. The Seebeck coefficient is essentially composition- and temperature-independent, the later suggesting the existence of an activated mobility associated with small polaron conduction. The optical gap measured remains constant near 2.6 eV while transparency increases with the substitution level, concomitant with a decrease in carrier content.Comment: Submitted for publicatio

Tunable Conductivity and Conduction Mechanism in an Ultraviolet Light Activated Electronic Conductor

A tunable conductivity has been achieved by controllable substitution of an ultraviolet light activated electronic conductor. The transparent conducting oxide system H-doped Ca12-xMgxAl14O33 (x=0,0.1,0.3,0.5,0.8,1.0) presents a conductivity that is strongly dependent on the substitution level and temperature. Four-point dc-conductivity decreases with x from 0.26 S/cm (x=0) to 0.106 S/cm (x=1) at room temperature. At each composition the conductivity increases (reversibly with temperature) until a decomposition temperature is reached; above this value, the conductivity drops dramatically due to hydrogen recombination and loss. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Mg-substituted system with x=0, 1, and 2. The Seebeck coefficient is essentially composition and temperature independent, the later suggesting the existence of an activated mobility associated with small polaron conduction. The optical gap measured remains constant near 2.6 eV while transparency increases with the substitution level, concomitant with a decrease in carrier content

Can scenario-planning support community-based natural resource management? Experiences from three countries in latin america

Community Based Natural Resource Management (CBNRM) is a concept critical to managing socio-ecological systems, but whose implementation needs strengthening. Scenario-planning is one approach that may offer benefits relevant to CBNRM, but whose potential is not yet well understood. We therefore designed, trialled and evaluated a scenario-planning method intended to support CBNRM at three cases, located in Colombia, Mexico and Argentina. Implementing scenario-planning was judged as worthwhile in all three cases, although aspects of it could be challenging to facilitate. The benefits generated were relevant to strengthening CBNRM: encouraging the participation of local people and using their knowledge; enhanced consideration and adaption of future change; and supporting the development of systems thinking. Tracing exactly when and how these benefits arise is challenging, but two elements of the method seemed particularly useful. Firstly, using a systematic approach to discuss how drivers of change may affect local socio-ecological systems helped to foster systems thinking and identify connections between issues. Secondly, explicitly focusing on how to use and respond to scenarios helped identify specific practical activities ('response options') that would support CBNRM despite the pressures of future change. Discussions about response options also highlighted the need for support by other actors (e.g. policy groups): this raises the question of when and how other actors and other sources of knowledge should be involved in scenario-planning, so as to encourage their buy-in to actions identified by the process. We suggest other CBNRM initiatives may benefit from adapting and applying scenario-planning. However, these initiatives should be carefully monitored since further research is required to understand how and when scenario-planning methods may produce benefits, and their strengths and weaknesses versus other methods

Enhanced Electronic Conductivity in Si-Substituted Calcium Aluminate

Improved conductivity has been achieved by controllable substitution of an ultraviolet electronic conductor. The transparent conducting oxide system, H-doped Ca12Al(14−x)SixO(33+x/2) with x=0−4, exhibits a conductivity strongly dependent on the substitution level. Four-point direct current conductivity increases with x from 0.15 to 0.61 S/cm at room temperature. The observed conductivity behavior is consistent with the predictions of our first principles density functional calculations for the Si-substituted system with x=0, 2, and 4. Furthermore, the Seebeck coefficient is composition dependent suggesting the existence of an activated mobility associated with small polaron conduction. ©2007 American Institute of Physic

Podcasts: An under-utilized form of science communication

Solar energy has sustained incredible technological advancement for several decades, driving down costs to allow rapid deployment of photovoltaic (PV) technology. However, public perception and understanding of these advancements is hard-pressed to keep up. The pace of information dissemination will become a limiting factor, in that public policy and practices will act on outdated information regarding PV tech. The PV community must engage in science communication and education practices appropriate for the new digital age to ensure a continued, increasing pace of PV deployment. To that end, the authors have created a podcast, and will share their findings on impact and best practices