The influence of the Rashba effect.

International audienc

Life-cycle energy use and environmental implications of high-performance perovskite tandem solar cells

A promising route to widespread deployment of photovoltaics is to harness inexpensive yet high-efficiency tandems. Perovskites are one of the most promising technologies to facilitate such a concept. Here we perform holistic analyses, from a life-cycle assessment perspective, on the energy payback time, greenhouse gas emission factor, and environmental impact scores for perovskite-silicon and perovskite-perovskite tandems benchmarked against state-of-the-art commercial silicon cells. The scalability of processing steps and materials, along with the uncertainty in the manufacture and operation of tandems, are explicitly considered to ensure realistic estimates of values. Notably, the resulting energy payback time and greenhouse gas emission factor of the all-perovskite tandem configuration are as low as 0.35 years and 10.7 g CO2-eq/kWh, respectively, compared to 1.52 years and 24.6 g CO2-eq/kWh for the silicon benchmark. Both tandem architectures demonstrate a substantial reduction in payback period by virtue of perovskites compared to silicon photovoltaics, but the greenhouse gas emission factors of the perovskite-silicon tandem are still dominated by silicon. Prolonging the lifetime provides a strong technological lever for bringing down the greenhouse gas emission factor such that even the perovskite-silicon tandem can outcompete the current benchmark on environmental factors as well as power and cost performance. Perovskite-perovskite tandems with flexible and lightweight form factors further cut these numbers down to 0.33 years and 10.0 g CO2-eq/kWh, and thus enhance the potential for large-scale, sustainable deployment.This work is supported in part by National Science Foundation (NSF) CAREER Award (CBET-1643244). S.D.S. acknowledges support from the Royal Society and Tata Group (UF150033) and the EPSRC (EP/R023980/1)

Heterogeneity at multiple length scales in halide perovskite semiconductors

Materials with highly crystalline lattice structures and low defect concentrations have classically been considered essential for high-performance optoelectronic devices. However, the emergence of high-efficiency devices based on halide perovskites is provoking researchers to rethink this traditional picture, as the heterogeneity in several properties within these materials occurs on a series of length scales. Perovskites are typically fabricated crudely through simple processing techniques, which leads to large local fluctuations in defect density, lattice structure, chemistry and bandgap that appear on short length scales (10 μm). Despite these variable and complex non-uniformities, perovskites maintain exceptional device efficiencies, and are, as of 2018, the best-performing polycrystalline thin-film solar cell material. In this Review, we highlight the multiple layers of heterogeneity ascertained using high-spatial-resolution methods that provide access to the required length scales. We discuss the impact that the optoelectronic variations have on halide perovskite devices, including the prospect that it is this very disorder that leads to their remarkable power-conversion efficiencies

Posterior mini-incision total hip arthroplasty controls the extent of post-operative formation of heterotopic ossification.

Heterotopic ossification (HO) is the formation of bone at extra-skeletal sites. Reported rates of HO after hip arthroplasty range from 8 to 90 %; however, it is only severe cases that cause problems clinically, such as joint stiffness. The effects of surgical-related controllable intra-operative risk factors for the formation of HO were investigated. Data examined included gender, age of patient, fat depth, length of operation, incision length, prosthetic fixation method, the use of pulsed lavage and canal brush, and component size and material. All cases were performed by the same surgeon using the posterior approach. A total of 510 cases of hip arthroplasty were included, with an overall rate of HO of 10.2 %. Longer-lasting operations resulted in higher grades of HO (p = 0.047). Incisions >10 cm resulted in more widespread HO formation (p = 0.021). No further correlations were seen between HO formation and fat depth, blood loss, instrumentation, fixation methods or prosthesis material. The mini-incision approach is comparable to the standard approach in the aetiology of HO formation, and whilst the rate of HO may not be controllable, a posterior mini-incision approach can limit its extent

Ambient Assistive Living (AAL) Technology for Dementia and Aging in Place: An inclusive approach to knowledge acquisition for the design community

The growing concern for safety, care and wellbeing of older people ad increase in age related health issues such as dementia, has generated a great interest in AAL technologies as a means to support the elderly and caregiver needs in daily living tasks, extend aging at home, and maintaining social inclusion for as long as possible. As technology becomes more ubiquitous in home environments, new design challenges will arise for the design/build community. Literature search revealed that there is now North American Guideline for AAL technology available. This study required an integrated design process utilizing in-person and online surveys which included interdisciplinary contributions from healthcare experts. building automation experts. interior designers and architects in the development of an educational structure fro a proposed North American AAL Technology Guideline. Research indicated that the educational structure would need to consider the developmental continuum in learning for professionals as they move from novice to expert in practice. Keywords: aging, ambient assisted living (AAL) technology, dementia, home automation, innovation models, Maslow's Hierarchy of Needs, professional developmental continuu

Photobrightening in Lead Halide Perovskites: Observations, Mechanisms, and Future Potential

There has been a meteoric rise in commercial potential of lead halide perovskite optoelectronic devices since photovoltaic cells (2009) and light emitting diodes (2014) based on these materials were first demonstrated. One key challenge common to each of these optoelectronic devices is the need to suppress non-radiative recombination, a process that limits the maximum achievable efficiency in photovoltaic cells and light emitting diodes. In this Progress Report, we dissect recent studies that seek to minimise this loss pathway in perovskites through a photobrightening effect, whereby the luminescence efficiency is enhanced through a light illumination passivation treatment. We highlight the sensitivity of this effect to experimental considerations such as atmosphere, photon energy, photon dose, and also the role of perovskite composition and morphology; under certain conditions there can even be photodarkening effects. Consideration of these factors is critical to resolve seemingly conflicting literature reports. We scrutinise proposed mechanisms, concluding that there is some consensus but further work is needed to identify the specific defects being passivated and elucidate universal mechanisms. Finally, we discuss the prospects for these treatments to minimise halide migration and push the properties of polycrystalline films towards those of their single-crystal counterparts

The Impact of Atmosphere on the Local Luminescence Properties of Metal Halide Perovskite Grains.

Metal halide perovskites are exceptional candidates for inexpensive yet high-performing optoelectronic devices. Nevertheless, polycrystalline perovskite films are still limited by nonradiative losses due to charge carrier trap states that can be affected by illumination. Here, in situ microphotoluminescence measurements are used to elucidate the impact of light-soaking individual methylammonium lead iodide grains in high-quality polycrystalline films while immersing them with different atmospheric environments. It is shown that emission from each grain depends sensitively on both the environment and the nature of the specific grain, i.e., whether it shows good (bright grain) or poor (dark grain) luminescence properties. It is found that the dark grains show substantial rises in emission, while the bright grain emission is steady when illuminated in the presence of oxygen and/or water molecules. The results are explained using density functional theory calculations, which reveal strong adsorption energies of the molecules to the perovskite surfaces. It is also found that oxygen molecules bind particularly strongly to surface iodide vacancies which, in the presence of photoexcited electrons, lead to efficient passivation of the carrier trap states that arise from these vacancies. The work reveals a unique insight into the nature of nonradiative decay and the impact of atmospheric passivation on the microscale properties of perovskite films

Nonradiative Losses in Metal Halide Perovskites

Metal halide perovskites are generating enormous interest for their use in solar cells and light-emission applications. One property linking the high performance of these devices is a high radiative efficiency of the materials; indeed, a prerequisite for these devices to reach their theoretical efficiency limits is the elimination of all nonradiative decay. Despite remarkable progress, there exists substantial parasitic nonradiative recombination in thin films of the materials and when interfaced into devices, and the origin of these processes is still poorly understood. In this Perspective, I will highlight key observations of these parasitic pathways on both the macro- and microscale in thin films and full devices. I will summarize our current understanding of the origin of nonradiative decay, as well as existing solutions that hint at facile ways to remove these processes. I will also show how these nonradiative decay pathways are intimately related to ionic migration, leading to the tantalizing conclusion that eliminating one phenomenon could in turn remove the other, ultimately pushing devices to their theoretical limits.This work has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement number PIOF-GA-2013-622630