One-pot synthesis of intercalating ZnO nanoparticles for enhanced dye-sensitized solar cells

In this letter we report a facile one-pot synthesis of intercalated ZnO particles for inexpensive, low-temperature solution processed dye-sensitised solar cells. High interconnectivity facilitates enhanced charge transfer between the ZnO nanoparticles and a consequent enhancement in cell efficiency. ZnO thin films were formed from a wide range of nanoparticle diameters which simultaneously increased optical scattering whilst enhancing dye loading. A possible growth mechanism was proposed for the synthesis of ZnO nanoparticles. The intercalated ZnO nanoparticle thin films were integrated into the photoanodes of dye-sensitised solar cells which showed an increase in performance of 37% compared to structurally equivalent cells employing ZnO nanowires. © 2012 Elsevier B.V.

Alternative approaches to slum upgrading in Kibera, Nairobi

This paper discusses the sustainability of two different approaches to upgrade water and sanitation infrastructure in Kenya's largest informal settlement, Kibera. A background to the urbanisation of poverty is outlined along with approaches to urban slums. Two case studies of completed interventions of infrastructure upgrading have been investigated. In one case study, the upgrading method driven by a non-government organisation uses an integrated livelihoods and partnership technique at community level to create an individual project. In the other case study, the method is a collaboration between the government and a multi-lateral agency to deliver upgraded services as part of a country-wide programme. The 'bottom-up' (project) and 'top-down' (programme) approaches both seek sustainability and aim to achieve this in the same context using different techniques. This paper investigates the sustainability of each approach. The merits and challenges of the approaches are discussed with the projected future of Kibera. The paper highlights the valuable opportunity for the role of appropriate engineering infrastructure for sustainable urban development, as well as the alleviation of poverty in a developing context.

On optical reflection at heterojunction interface of thin film solar cells

Heterojunction is an important structure for the development of photovoltaic solar cells. In contrast to homojunction structures, heterojunction solar cells have internal crystalline interfaces, which will reflect part of the incident light, and this has not been considered carefully before though many heterostructure solar cells have been commercialized. This paper discusses the internal reflection for various material systems used for the development of heterostructure-based solar cells. It has been found that the most common heterostructure solar cells have internal reflection less than 2%, while some potential heterojunction solar cells such as ITO/GaAs, ITO/InP, Si/Ge, polymer/semiconductors and oxide semiconductors may have internal reflection as high as 20%. Also it is worse to have a window layer with a lower refractive index than the absorption layer for solar cells. Ignoring this strong internal reflection will lead to severe deterioration and reduction of conversion efficiency; therefore measures have to be taken to minimize or prevent this internal reflection. © 2013 Elsevier B.V.

Spray drying: An alternative synthesis method for polycationic oxide compounds

Synthesis of polycationic compounds by the spray-drying technique is an interesting alternative in the domain of aqueous precursor synthesis methods. Spray drying yields high quality samples with good reproducibility. The possibility of scaling up for production of large quantities with fast processing time is well established by the commercial availability of powders of various compositions. In this paper, we have discussed the advantages and limitations of this method and demonstrated its interest by synthesizing a few polycationic compounds selected for their attractive properties of thermoelectricity [Bi1.68Ca2Co1.69O 8, La0.95A0.05CoO3 (A=Ca, Sr, Ba)] or magnetoresistance [La0.70A0.30MnO3 (A=Sr, Ba)]. We have confirmed the quality of these samples by reporting their structure, magnetic and transport properties. © 2010 Elsevier Ltd All rights reserved.

Simulating early adoption of alternative fuel vehicles for sustainability

We quantify the conditions that might trigger wide spread adoption of alternative fuel vehicles (AFVs) to support energy policy. Empirical review shows that early adopters are heterogeneous motivated by financial benefits, environmental appeal, new technology, and vehicle reliability. A probabilistic Monte Carlo simulation model is used to assess consumer heterogeneity for early and mass market adopters. For early adopters full battery electric vehicles (BEVs) are competitive but unable to surpass diesels or hybrids due to purchase price premium and lack of charging availability. For mass adoption, simulations indicate that if the purchase price premium of a BEV closes to within 20% of an in-class internal combustion engine (ICE) vehicle, combined with a 60% increase in refuelling availability relative to the incumbent system, BEVs become competitive. But this depends on a mass market that values the fuel economy and CO2 reduction benefits associated with BEVs. We also find that the largest influence on early adoption is financial benefit rather than pro-environmental behaviour suggesting that AFVs should be marketed by appealing to economic benefits combined with pro-environmental behaviour to motivate adoption. Monte Carlo simulations combined with scenarios can give insight into diffusion dynamics for other energy demand-side technologies. © 2012 Elsevier Inc.

A survey of alternative once-through fast reactor core designs

Reprocessing of Light Water Reactor (LWR) spent fuel to recover plutonium or transuranics for use in Sodium cooled Fast Reactors (SFRs) is a distant prospect in the U.S.A. This has motivated our evaluation of potentially cost-effective operation of uranium startup fast reactors (USFRs) in a once-through mode. This review goes beyond findings reported earlier based on a UC fueled MgO reflected SFR to describe a broader parametric study of options. Cores were evaluated for a variety of fuel/coolant/reflector combinations: UC/UZr/UO 2/UN;Na/Pb; MgO/SS/Zr. The challenge is achieving high burnup while minimizing enrichment and respecting both cladding fluence/dpa and reactivity lifetime limits. These parametric studies show that while UC fuel is still the leading contender, UO 2 fuel and ZrH 1.7 moderated metallic fuel are also attractive if UC proves to be otherwise inadequate. Overall, these findings support the conclusion that a competitive fuel cycle cost and uranium utilization compared to LWRs is possible for SFRs operated on a once-through uranium fueled fuel cycle. In addition, eventual transition to TRU recycle mode is studied, as is a small test reactor to demonstrate key features.

The effect of dislocations on the efficiency of InGaN/GaN solar cells

Two solar cells based on an InGaN/GaN p-i-n hetero-junction, but having different dislocation densities, were fabricated and characterized. The structures were grown on c-plane (0001) GaN-on-sapphire templates with different threading dislocation (TD) densities of 5×108 and 5×109 cm-2. Structural characterization revealed the presence of V-defects in the InGaN epilayer. Since each V-defect was associated with a TD, the structural as well as the optical properties worsened with a higher TD density in the GaN/sapphire template. It was also found that additional dislocations were generated in the p-GaN layer over the V-defects in the InGaN layer. Because of its superior structural quality, the peak external quantum efficiency (EQE) of the low TD density sample was three times higher than that of the high TD density sample. © 2013 Elsevier B.V.