Band gap and work function tailoring of SnOfor improved transparent conducting ability in photovoltaics

Transparent conducting oxides (TCOs) are an essential component in modern optoelectronic devices, such as solar panels and touch screens. Their ability to combine transparency and conductivity, two properties that are normally mutually exclusive, have made them the subject of intense research over the last 50 years. SnO2, doped with F or Sb, is a widely used and relatively inexpensive transparent conducting material, however, its electronic structure leaves scope for improving its properties for use in many TCO applications, especially in solar cell devices. Here we show using density functional theory that incorporation of Pb into SnO2 reduces the band gap through lowering of the conduction band minimum, thereby increasing the electron affinity. The electron effective mass at the conduction band minimum decreases alongside the band gap, indicating improved charge carrier mobilities. Furthermore, the calculated optical absorption properties show the alloys retain their transparency in the visible spectrum. Our results suggest that alloying of PbO2 with SnO2 will enable improved electronic properties, including a highly tuneable workfunction, which will open up the material for other applications, such as hole injection layers in organic photovoltaics

Beyond methylammonium lead iodide: prospects for the emergent field of ns(2) containing solar absorbers

The field of photovoltaics is undergoing a surge of interest following the recent discovery of the lead hybrid perovskites as a remarkably efficient class of solar absorber. Of these, methylammonium lead iodide (MAPI) has garnered significant attention due to its record breaking efficiencies, however, there are growing concerns surrounding its long-term stability. Many of the excellent properties seen in hybrid perovskites are thought to derive from the 6s(2) electronic configuration of lead, a configuration seen in a range of post-transition metal compounds. In this review we look beyond MAPI to other ns(2) solar absorbers, with the aim of identifying those materials likely to achieve high efficiencies. The ideal properties essential to produce highly efficient solar cells are discussed and used as a framework to assess the broad range of compounds this field encompasses. Bringing together the lessons learned from this wide-ranging collection of materials will be essential as attention turns toward producing the next generation of solar absorbers

Pathological response for neoadjuvant chemotherapy in locally advanced breast cancer at NCI, Sudan: 6 years’ experience

Background: Breast cancer is the leading cancer in Sudanese females.Objectives: This study was done to evaluate the clinical response to neoadjuvant chemotherapy for patients treated at National Cancer Institute (NCI) and to compare it with the published literature.Methods: This is a retrospective study conducted in National Cancer Institute (NCI), Gezira State, Sudan during the period from April 2005 to August 2011. We studied the data for all patients who have locally  advanced breast cancer and treated at NCI during study period. Patients who remained inoperable after treatment were considered as having no response to therapy. Data were introduced and analyzed using SPSS software. Data evaluated includes Patient age, disease stage,  chemotherapy regimens, and number of cycles, tumor histology, grade and histopathology after chemotherapy.Results: A total of 110 patients who received neoadjuvant chemotherapy and fulfilled criteria for inclusion during the period 2005 to 2011 were evaluated. Majority of patients were between 30-50 years of age (63%). Patients who achieved response and had surgery were 65%. Among those who underwent surgery 22% have complete pathological response. Most of patients who achieved complete histopathological response had six cycles of chemotherapy.Conclusion: this study demonstrated that neoadjuvant systemic therapy is an accepted approach for women with locally advanced breast cancer for whom immediate surgery is inappropriate, and we achieved results similar to the international literature.Key words: breast cancer, neoadjuvant, chemotherapy, response, NCI, Sudan

First-principles insights into tin-based two-dimensional hybrid halide perovskites for photovoltaics

The two-dimensional (2D) hybrid halide perovskites have recently attracted attention due to their excellent photovoltaic performance. In comparison to their three-dimensional (3D) analogues, they show superior long-term durability and moisture tolerance. Meanwhile, their layered topology offers greater flexibility for electronic structure tuning. To date, most devices containing 2D perovskites have been based on Pb, which presents environment concerns and a possible roadblock to commercialisation due to its toxicity. The development of lead-free alternatives is therefore immensely important to facilitate the uptake of perovskite-based photovoltaics. Herein, we investigate the geometrical, electronic and optical properties of the semiconducting 2D tin perovskites (CH 3 (CH 2 ) 3 NH 3 ) 2 (CH 3 NH 3 ) n-1 Sn n I 3n+1 (n = 1, 2 and 3), using relativistic hybrid density functional theory calculations. We demonstrate that the band gaps of the series decrease with increasing perovskite-like layer thickness, from 1.85 eV (n = 1) to 1.38 eV (n = 3). We find strong and broad optical absorption across the series, in addition to small effective masses of electrons and holes in the laminar plane. The n = 3 composition displays a high spectroscopic limited maximum efficiency of 24.6%. Our results indicate this series of homologous 2D tin halide perovskites are a promising class of stable and efficient light-absorbing materials for photovoltaics

Defect Tolerance to Intolerance in the Vacancy-Ordered Double Perovskite Semiconductors Cs2SnI6 and Cs2TeI6.

Vacancy-ordered double perovskites of the general formula A2BX6 are a family of perovskite derivatives composed of a face-centered lattice of nearly isolated [BX6] units with A-site cations occupying the cuboctahedral voids. Despite the presence of isolated octahedral units, the close-packed iodide lattice provides significant electronic dispersion, such that Cs2SnI6 has recently been explored for applications in photovoltaic devices. To elucidate the structure-property relationships of these materials, we have synthesized solid-solution Cs2Sn1-xTexI6. However, even though tellurium substitution increases electronic dispersion via closer I-I contact distances, the substitution experimentally yields insulating behavior from a significant decrease in carrier concentration and mobility. Density functional calculations of native defects in Cs2SnI6 reveal that iodine vacancies exhibit a low enthalpy of formation, and that the defect energy level is a shallow donor to the conduction band rendering the material tolerant to these defect states. The increased covalency of Te-I bonding renders the formation of iodine vacancy states unfavorable and is responsible for the reduction in conductivity upon Te substitution. Additionally, Cs2TeI6 is intolerant to the formation of these defects, because the defect level occurs deep within the band gap and thus localizes potential mobile charge carriers. In these vacancy-ordered double perovskites, the close-packed lattice of iodine provides significant electronic dispersion, while the interaction of the B- and X-site ions dictates the properties as they pertain to electronic structure and defect tolerance. This simplified perspective based on extensive experimental and theoretical analysis provides a platform from which to understand structure-property relationships in functional perovskite halides

Perception of Nurses about Palliative Care: Experience from South-West Nigeria

Background: Nurses play a major role all over the world in the palliative care team.Aim: The aim of this study was to investigate the knowledge and attitude of nurses toward palliative care in a tertiary level hospital in Nigeria. Subjects and Methods: Setting: This cross-sectional questionnaire-based study was carried out among nurses at a tertiary health care facility inAdo-Ekiti, South-West Nigeria. Design: A cross-sectional questionnaire-based study was carried out. The questionnaire sought information about the sociodemographic profile of respondents, their knowledge of definition and philosophy of palliative care among other things. Descriptive statistics was used to obtain the general characteristics of the study participants, while Chi-square was used to determine the association between categorical variables. A two-sided P < 0.05 was considered as significant.Results: A total of 100 questionnaires were returned with a female preponderance among the respondents with F: M ratio of 9:1. Regarding the definition of palliative care, 71.8% (48/66) of the respondents  understood palliative care to be about pain medicine, 55% (33/60) thought it to be geriatric medicine, while 90.2% (83/92) felt palliative care is about the active care of the dying. Exactly 80.5% (66/82) respondents agreedthat palliative care recognizes dying as a normal process while 84.1% (74/88) respondents were of the opinion that all dying patients would require palliative care. The use of morphine would improve the quality of life of patients according to 68.9% (42/61) of respondents.Conclusion: There are gaps in the knowledge of healthcare workers in the area of palliative care and this call for a review of the current nursing curriculum and practice guidelines in Nigeria.Keywords: End of life, Nursesf attitude, Pain management, Palliative car