Black Ultra-Thin Crystalline Silicon Wafers Reach the 4n2 Absorption Limit-Application to IBC Solar Cells

Cutting costs by progressively decreasing substrate thickness is a common theme in the crystalline silicon photovoltaic  industry for the last decades, since drastically thinner wafers would significantly reduce the substrate-related costs. In addition to the technological challenges concerning wafering and handling of razor-thin flexible wafers, a major bottleneck is to maintain high absorption in those thin wafers. For the latter, advanced light-trapping techniques become of paramount importance. Here we demonstrate that by applying state-of-the-art black-Si nanotexture produced by DRIE on thin uncommitted wafers, the maximum theoretical absorption (Yablonovitch's 4n2 absorption limit), that is, ideal light trapping, is reached with wafer thicknesses as low as 40, 20, and 10 µm when paired with a back reflector. Due to the achieved promising optical properties the results are implemented into an actual thin interdigitated back contacted solar cell. The proof-of-concept cell, encapsulated in glass, achieved a 16.4% efficiency with an JSC  = 35 mA cm- 2 , representing a 43% improvement in output power with respect to the reference polished cell. These results demonstrate the vast potential of black silicon nanotexture in future extremely-thin silicon photovoltaics.

Urban green space and mental health among people living alone: The mediating roles of relational and collective restoration in an 18-country sample

Rates of living alone, especially in more urbanised areas, are increasing across many industrialised countries, with associated increases in feelings of loneliness and poorer mental health. Recent studies have suggested that access to nature (e.g. parks and green spaces) can reduce the stressors associated with loneliness, partly through providing opportunities to nurture personal relationships (relational restoration) and engage in normative community activities (collective restoration). Such associations might vary across different household compositions and socio-demographic or geographical characteristics, but these have not been thoroughly tested. Using data collected across 18 countries/territories in 2017-2018, we grouped urban respondents into those living alone (n = 2062) and those living with a partner (n = 6218). Using multigroup path modelling, we tested whether the associations between neighbourhood greenspace coverage (1-km-buffer from home) and mental health are sequentially mediated by: (a) visits to greenspace; and subsequently (b) relationship and/or community satisfaction, as operationalisations of relational and collective restoration, respectively. We also tested whether any indirect associations varied among subgroups of respondents living alone. Analyses showed that visiting green space was associated with greater mental well-being and marginally lower odds of using anxiety/depression medication use indirectly, mediated via both relationship and community satisfaction. These indirect associations were equally strong among respondents living alone and those living with a partner. Neighbourhood green space was, additionally, associated with more visits among respondents living with a partner, whereas among those living alone, this was sensitive to the green space metric. Within subgroups of people living alone, few overall differences were found. Some indirect pathways were, nevertheless, stronger in males, under 60-year-olds, those with no financial strain, and residents in warmer climates. In conclusion, supporting those living alone, as well as those living with a partner, to more frequently access their local greenspaces could help improve mental health via promoting relational and collective restoration.

Special Issue: Place, Space, and Mental Health

Global megatrends, including climate change and urbanisation, are shaping and changing how we live in the future [...].

Use of Health Services Among People Living Alone in Finland

Although health issues are more common in people living alone than in those living with someone, research on the service use of people living alone has focused on older age groups. Based on large Finnish cross-sectional health survey (FinHealth 2017, n = 4686), we examined the difference in the use and assessment of health services between those living alone and those living with someone, and whether some sub-groups within those living alone use or perceive the use of health care services differently to those living with someone. The adjusted proportions, based on logistic regression models controlling for demographic variables and perceived health and mental health, showed that those living alone had seen a doctor in the past year less often (65.5%) than those not living alone (71.9%). People living alone had also less often had a health examination in the past 5 years (72.4%) than those not living alone (79.2%), and this proportion was particularly low within people living alone with high levels of depressive symptoms (59.0%) compared to lower levels (75.0%). Conclusively, among people living alone, those who suffer from depressive symptoms might be a potential group that does not receive the same levels of preventive care than others.

Profiles of subjective health among people living alone: a latent class analysis

Background

Living alone has increased globally and especially in Finland where 45% of all households are single occupancy. Epidemiological research has found that living alone a risk factor for a wide range of adversities related to quality of life but the rapidly-changing demographics of people living alone calls for a more detailed investigation of their subjective health status.

Methods

Using a cross-sectional survey sent for a random sample of Finnish residents in single-person households (n = 884), we explored with latent class analysis whether the respondents form different health profiles based on the three health dimensions defined by the World Health Organization: physical, social, and mental well-being. The identified groups were then compared in terms of demographic characteristics with the χ² test and quality of life using linear regression models. Sensitivity analyses were run using more refined, manual 3-step BCH method.

Results

Four distinct health profiles were found: Languishing (4%), Managing (35%), Healthy (30%), and Flourishing (31%). The groups differed in most socio-demographic aspects such as marital and employment status, but not in terms of geographic location or gender (apart from group Languishing that contained more men). Controlling for these socio-demographic differences, all groups showed different average levels of perceived quality of life to the expected direction.

Conclusions

Our findings suggest that people living alone are indeed a very heterogeneous group in terms of subjective health. Instead of seeing living alone as a mere risk for low quality of life, concept of living alone should be understood more broadly both in public discussion and scientific research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-11396-2.

Positive Mental Health of Finnish People Living Alone: The Role of Circumstantial Factors and Leisure-Time Activities

Living alone has become more common across Europe. Past research has consistently identified living alone as a risk factor for poor mental health while evidence on the positive dimension(s) of mental health has been scarce. Positive mental health has been associated with rather stable circumstantial factors, such as socio-economic characteristics and social relationships, and day-to-day activities in the form of leisure participation, in general populations. In this study, our objective was to assess these relationships among people living alone. We specified a structural equation model in a random sample of Finnish people living alone (n = 884), with the circumstantial factors as (exogenous) explanatory variables, participation in various leisure activities as mediators, and positive mental health as the outcome. In the model, more frequent engagement in several leisure-time activities, including being in contact with family/friends and physical activity in nature, were positively associated with positive mental health. The circumstantial factors that most strongly explained both leisure participation and positive mental health were the number of friends, being in a relationship, and having no limiting illnesses. In conclusion, among Finnish people living alone, social and functional factors appear to be more strongly associated with leisure participation and positive mental health than socio-economic factors.

Black-Silicon Ultraviolet Photodiodes Achieve External Quantum Efficiency above 130

At present, ultraviolet sensors are utilized in numerous fields ranging from various spectroscopy applications via biotechnical innovations to industrial process control. Despite this, the performance of current UV sensors is surprisingly poor. Here, we break the theoretical one-photon-one-electron barrier and demonstrate a device with a certified external quantum efficiency above 130% in UV range without external amplification. The record high performance is obtained using a nanostructured silicon photodiode with self-induced junction. We show that the high efficiency is based on effective utilization of multiple carrier generation by impact ionization taking place in the nanostructures. While the results can readily have a significant impact on the UV-sensor industry, the underlying technological concept can be applied to other semiconductor materials, thereby extending above unity response to longer wavelengths and offering new perspectives for improving efficiencies beyond the Shockley-Queisser limit.

Neighbourhood blue space, health and wellbeing: The mediating role of different types of physical activity

BACKGROUND

Evidence suggests that living near blue spaces such as the coast, lakes and rivers may be good for health and wellbeing. Although greater levels of physical activity (PA) may be a potential mechanism, we know little about the types of PA that might account for this.

OBJECTIVES

To explore the mediating role of: a) 'watersports' (e.g. sailing/canoeing); b) 'on-land outdoor PA' in natural/mixed settings (e.g. walking/running/cycling); and, c) 'indoor/other PA' (e.g. gym/squash) in the relationships between residential blue space availability and health outcomes.

METHODS

Using data from the Health Survey for England (n = 21,097), we constructed a path model to explore whether weekly volumes of each PA type mediate any of the relationships between residential blue space availability (coastal proximity and presence of freshwater) and self-reported general and mental health, controlling for green space density and a range of socio-economic factors at the individual- and area-level.

RESULTS

Supporting predictions, living nearer the coast was associated with better self-reported general and mental health and this was partially mediated by on-land outdoor PA (primarily walking). Watersports were more common among those living within 5kms of the coast, but did not mediate associations between coastal proximity and health. Presence of freshwater in the neighbourhood was associated with better mental health, but this effect was not mediated by PA.

CONCLUSIONS

Although nearby blue spaces offer potentially easier access to watersports, relatively few individuals in England engage in them and thus they do not account for positive population health associations. Rather, the benefits to health from coastal living seem, at least in part, due to participation in land-based outdoor activities (especially walking). Further research is needed to explore the mechanisms behind the relationship between freshwater presence and mental health.

The relationship between perceived health and physical activity indoors, outdoors in built environments, and outdoors in nature

Background:

A body of evidence shows that both physical activity and exposure to nature are connected to improved general and mental health. Experimental studies have consistently found short term positive effects of physical activity in nature compared with built environments. This study explores whether these benefits are also evident in everyday life, perceived over repeated contact with nature. The topic is important from the perspectives of city planning, individual well-being, and public health.

Methods:

National survey data (n = 2,070) from Finland was analysed using structural regression analyses. Perceived general health, emotional well-being, and sleep quality were regressed on the weekly frequency of physical activity indoors, outdoors in built environments, and in nature. Socioeconomic factors and other plausible confounders were controlled for.

Results:

Emotional well-being showed the most consistent positive connection to physical activity in nature, whereas general health was positively associated with physical activity in both built and natural outdoor settings. Better sleep quality was weakly connected to frequent physical activity in nature, but the connection was outweighed by other factors.

Conclusion:

The results indicate that nature provides an added value to the known benefits of physical activity. Repeated exercise in nature is, in particular, connected to better emotional well-being.