Thiol and Halometallate, Mutually Passivated Quantum Dot Ink for Photovoltaic Application.

Tunable-band-gap colloidal QDs are a potential building block to harvest the wide-energy solar spectrum. The solution-phase surface passivation with lead halide-based halometallate ligands has remarkably simplified the processing of quantum dots (QDs) and enabled the proficient use of materials for the development of solar cells. It is, however, shown that the hallometalate ligand passivated QD ink allows the formation of thick crystalline shell layer, which limits the carrier transport of the QD solids. Organic thiols have long been used to develop QD solar cells using the solid-state ligand exchange approach. However, their use is limited in solution-phase passivation due to poor dispersity of thiol-treated QDs in common solvents. In this report, a joint passivation strategy using thiol and halometallate ligand is developed to prepare the QD ink. The mutually passivated QDs show a 50% reduction in shell thickness, reduced trap density, and improved monodispersity in their solid films. These improvements lead to a 4 times increase in carrier mobility and doubling of the diffusion length, which enable the carrier extraction from a much thicker absorbing layer. The photovoltaic devices show a high efficiency of 10.3% and reduced hysteresis effect. The improvement in surface passivation leads to reduced oxygen doping and improved ambient stability of the solar cells.

Early Excision and Grafting in Burns: An Experience in a Tertiary Care Industrial Hospital of Eastern India.

Introduction To compare the burn patients undergoing early excision and grafting (within 7 days of burn injury) with the patients undergoing late surgeries (more than 7 days after burn injury) to see if there was any difference in surgical and outcome parameters including length of stay, expenditure, and overall outcome of the patients. Material and Methods A retrospective analysis of the data collected from the burn care unit records over a period of one year was done. Fifty-eight patients who matched with our inclusion criteria were divided into two groups. An early excision group who underwent surgery within 7 days of sustaining burn injury ( n = 24) and a late excision group who underwent excision and grafting/debridement after 7 days of sustaining burn ( n = 34). Data recorded included demographic variables like age, sex, percentage total body surface area (TBSA) burn; nature of burn; date of sustaining burn; date of admission to the burn care unit; and treatment and outcome parameters like date of surgery, days from burn injury to first surgery, number of surgeries, type of surgery, percentage of TBSA resurfaced with skin graft, blood products used, length of stay, outcome, and total expenditure incurred by patients. Results There was no statistically significant difference in the number of surgeries done, the units of packed cell used, and the number of fresh frozen plasma (FFP) used between the early excision group and the late excision group. The length of stay was significantly low in the early excision group as compared with the late excision group. The expenditure incurred in the treatment of the early excision group was significantly lower than the cost of treatment of the late excision group. Conclusion Early excision and grafting in burn cases reduces the length of the stay of burn patients and, in turn, reduces the cost of treatment. However, having a dedicated burn care unit is important for the hospitals and both public and private hospitals should make a move in that direction.

Generic and Scalable Method for the Preparation of Monodispersed Metal Sulfide Nanocrystals with Tunable Optical Properties.

A rational synthetic method that produces monodisperse and air-stable metal sulfide colloidal quantum dots (CQDs) in organic nonpolar solvents using octyl dithiocarbamic acid (C8DTCA) as a sulfur source, is reported. The fast decomposition of metal-C8DTCA complexes in presence of primary amines is exploited to achieve this purpose. This novel technique is generic and can be applied to prepare diverse CQDs, like CdS, MnS, ZnS, SnS, and In2S3, including more useful and in-demand PbS CQDs and plasmonic nanocrystals of Cu2S. Based on several control reactions, it is postulated that the reaction involves the in situ formation of a metal-C8DTCA complex, which then reacts in situ with oleylamine at slightly elevated temperature to decompose into metal sulfide CQDs at a controlled rate, leading to the formation of the materials with good optical characteristics. Controlled sulfur precursor's reactivity and stoichiometric reaction between C8DTCA and metal salts affords high conversion yield and large-scale production of monodisperse CQDs. Tunable and desired crystal size could be achieved by controlling the precursor reactivity by changing the reaction temperature and reagent ratios. Finally, the photovoltaic devices fabricated from PbS CQDs displayed a power conversion efficiency of 4.64% that is comparable with the reported values of devices prepared with PbS CQDs synthesized by the standard methods.

The role of surface ligands in determining the electronic properties of quantum dot solids and their impact on photovoltaic figure of merits.

Surface chemistry plays a crucial role in determining the electronic properties of quantum dot solids and may well be the key to mitigate loss processes involved in quantum dot solar cells. Surface ligands help to maintain the shape and size of the individual dots in solid films, to preserve the clean energy band gap of the individual particles and to control charge carrier conduction across solid films, in turn regulating their performance in photovoltaic applications. In this report, we show that the changes in size, shape and functional groups of small chain organic ligands enable us to modulate mobility, dielectric constant and carrier doping density of lead sulfide quantum dot solids. Furthermore, we correlate these results with performance, stability and recombination processes in the respective photovoltaic devices. Our results highlight the critical role of surface chemistry in the electronic properties of quantum dots. The role of the size, functionality and the surface coverage of the ligands in determining charge transport properties and the stability of quantum dot solids have been discussed. Our findings, when applied in designing new ligands with higher mobility and improved passivation of quantum dot solids, can have important implications for the development of high-performance quantum dot solar cells.

Cost of providing inpatient burn care in a tertiary, teaching, hospital of North India.

There is an extreme paucity of studies examining cost of burn care in the developing world when over 85% of burns take place in low and middle income countries. Modern burn care is perceived as an expensive, resource intensive endeavour, requiring specialized equipment, personnel and facilities to provide optimum care. If 'burn burden' of low and middle income countries (LMICs) is to be tackled deftly then besides prevention and education we need to have burn centres where 'reasonable' burn care can be delivered in face of resource constraints. This manuscript calculates the cost of providing inpatient burn management at a large, high volume, tertiary burn care facility of North India by estimating all cost drivers. In this one year study (1st February to 31st January 2012), in a 50 bedded burn unit, demographic parameters like age, gender, burn aetiology, % TBSA burns, duration of hospital stay and mortality were recorded for all patients. Cost drivers included in estimation were all medications and consumables, dressing material, investigations, blood products, dietary costs, and salaries of all personnel. Capital costs, utility costs and maintenance expenditure were excluded. The burn unit is constrained to provide conservative management, by and large, and is serviced by a large team of doctors and nurses. Entire treatment cost is borne by the hospital for all patients. 797 patients (208 <12 years old) with acute burn were admitted with a mean age of 23.04 years (range 18 days to 83 years). The mean BSA burn was 42.26% (ranging from 2% to 100%). 378/797 patients (47.43%) sustained up to 30% BSA burns, 216 patients (27.1%) had between 31 and 60% BSA and 203 patients (25.47%) had >60% BSA burns. 258/797 patients died (32.37%). Of these deaths 16, 68 and 174 patients were from 0 to 30%, 31 to 60% and >60% BSA groups, respectively. The mean length of hospitalization for all admissions was 7.86 days (ranging from 1 to 62 days) and for survivors it was 8.9 days. There were 299 operations carried out in the dedicated burns theatre. The total expenditure for the study period was Indian Rupees (Rs) 46,488,067 or US$ 845,237. At 1 US$=Rs 55 it makes the cost per patient to be US$ 1060.5. Almost 70% of cost of burn management resulted from salaries, followed by investigations (11.56%) and dressings (8.24%). The mean cost of investigations per patient was Rs 6742.46 (US$ 122.59). Only 147/797 patients received 322 units of blood. Thus, the average cost of blood transfusion for all admissions was Rs 521.17 (US$ 9.47). Our study is evidence to direct costs of providing burn care in a tertiary centre of a low income country, and the large number of patients in our study while averaging the costs also validates the estimates. The 'reasonability' of care being delivered is defined by adequate resuscitation, daily topical dressings, appropriate surgery (escharotomy, debridement, and skin grafting), adequate nutrition and physical therapy. The 'reasonability' of outcomes can be measured by mortality figures. The bottom line of management is strict observation by burn staff. The low mean hospital stay also reflects our admission and discharge policy which is to benefit the maximum number of patients who require resuscitative/intensive care, and who have extensive and deep wounds, or injury of critical nature. We conclude that providing burn care based on our model can be emulated in other LICs as the costing is driven by 'necessity of expense' rather than 'ability to spend'.