Transparent selective contacts for silicon-based heterojunction solar cells

Renewable energies are nowadays recognised to be the protagonists of a necessary sustainable transition in the energy production process. Among the existing technologies, photovoltaic (PV) stands out for the infinite availability of the source, the direct efficient energy transformation and for low global energy costs. These reasons drive the global research toward materials and methods to obtain higher and higher efficiencies. Beyond the well-assessed silicon-based homojunction technology, that covers the 95% of the total PV production, the amorphous/crystalline-silicon heterojunction concept is gaining increasing market share. Heterojunctions (HJs) are able to overcome some shortcomings of homojunctions, such as the high thermal budget connected to the diffusion process to achieve the doping and to the recombination losses that limit the VOC. However HJs still require complex architectures and the use of toxic and dangerous gases, which demand costly measures for a safe industrial manufacturing. A new approach to circumvent some of the above-mentioned issues is currently explored with increasing interest, and involves the use of non-doped, non-silicon films to replace the amorphous-silicon ones. A great variety of materials has already been proposed and tested for the purpose, but some challenges still have to be completely solved, first of all the resistance to thermal annealing at 200-250°C, that is a necessary step in module assembling. Moreover, in view of an industrial application, the manufacture of these novel materials needs to satisfy several constrains and then guarantee an easy and high-throughput process. In this thesis the attention is focused on some of these novel materials for both emitter and base contacts of a heterostructure solar cell based on n-type doped crystalline silicon. In particular nickel oxide and titanium oxide or zinc sulphide are exploited as selective emitter and base contact respectively. These materials have to be more transparent than the doped amorphous layer counterpart to enhance the quantum yield of the solar cell in the blue region of the solar spectrum where the amorphous films introduce parasitic absorptions. Moreover the substitute layers must be deposited on the well-assessed thin buffer layer of amorphous silicon suboxide used in our laboratory to passivate the surfaces of the silicon wafer, therefore the most relevant constrain to fulfil is to avoid any contamination and any detrimental thermal stress of the surface passivation. On the basis of these requirements, particular care will be given to the choice of the deposition procedures as well as to the choice of the doping elements to be introduced into the selective contacts. The measurement of silicon surface passivation will be adopted as the most relevant method to evaluate the suitability of materials and manufacturing methods. Numerical simulations will also be used to evaluate the ideal band diagram of the proposed heterostructures and to verify how differences in the experimental properties of the materials with respect to ideality could affect the heterostructure device performances. In analogy with the doped amorphous layers used in conventional HJs, also the proposed novel materials for selective contacts need to be coupled to a transparent conductive oxide to make up for the poor lateral conductivity that still remains a basic issue of any selective layer proposed in the literature up to now. In this thesis another promising material is tested as an alternative to indium tin oxide, namely tungsten-doped indium oxide. It is found that non-reactive radio-frequency sputtering is suited to grow transparent films with very high mobility and low resistivity due a low carrier concentration that reduces parasitic absorptions. Most importantly, the sputtering damage to surface passivation of the crystalline silicon substrates can be completely recovered after a suitable thermal annealing. All the discussed results show that ideal materials or totally qualified deposition methods for obtaining alternative selective contacts have yet to be found, mostly from the point of view of the resistance to thermal treatments. This thesis adds some tiles to the road to high-efficiency, low-thermal budget, low-toxicity, high-throughput silicon-based heterojunctions

Anti-vascular endothelial growth factor for diabetic macular oedema.

BACKGROUND: Diabetic macular oedema (DMO) is a common complication of diabetic retinopathy. Although grid or focal laser photocoagulation has been shown to reduce the risk of visual loss in DMO, or clinically significant macular oedema (CSMO), vision is rarely improved. Antiangiogenic therapy with anti-vascular endothelial growth factor (anti-VEGF) modalities is used to try to improve vision in people with DMO. OBJECTIVES: To investigate the effects in preserving and improving vision and acceptability, including the safety, compliance with therapy and quality of life, of antiangiogenic therapy with anti-VEGF modalities for the treatment of DMO. SEARCH METHODS: We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2014, Issue 3), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to April 2014), EMBASE (January 1980 to April 2014), Latin American and Caribbean Health Sciences Literature Database (LILACS) (January 1982 to April 2014), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 28 April 2014. SELECTION CRITERIA: We included randomised controlled trials (RCTs) comparing any antiangiogenic drugs with an anti-VEGF mechanism of action versus another treatment, sham treatment or no treatment in people with DMO. DATA COLLECTION AND ANALYSIS: We used standard methodological procedures expected by The Cochrane Collaboration. The risk ratios (RR) for visual loss and visual gain of three or more lines of logMAR visual acuity were estimated at one year of follow-up (plus or minus six months) after treatment initiation. MAIN RESULTS: Eighteen studies provided data on four comparisons of interest in this review. Participants in the trials had central DMO and moderate vision loss.Compared with grid laser photocoagulation, people treated with antiangiogenic therapy were more likely to gain 3 or more lines of vision at one year (RR 3.6, 95% confidence interval (CI) 2.7 to 4.8, 10 studies, 1333 cases, high quality evidence) and less likely to lose 3 or more lines of vision (RR 0.11, 95% CI 0.05 to 0.24, 7 studies, 1086 cases, high quality evidence). In meta-analyses, no significant subgroup difference was demonstrated between bevacizumab, ranibizumab and aflibercept for the two primary outcomes, but there was little power to detect a difference. The quality of the evidence was judged to be high, because the effect was large, precisely measured and did not vary across studies, although some studies were at high or unclear risk of bias for one or more domains. Regarding absolute benefit, we estimated that 8 out of 100 participants with DMO may gain 3 or more lines of visual acuity using photocoagulation whereas 28 would do so with antiangiogenic therapy, meaning that 100 participants need to be treated with antiangiogenic therapy to allow 20 more people (95% CI 13 to 29) to markedly improve their vision after one year. People treated with anti-VEGF on average had 1.6 lines better vision (95% CI 1.4 to 1.8) after one year compared to laser photocoagulation (9 studies, 1292 cases, high quality evidence). To achieve this result, seven to nine injections were delivered in the first year and three or four in the second, in larger studies adopting either as needed regimens with monthly monitoring or fixed regimens.In other analyses antiangiogenic therapy was more effective than sham (3 studies on 497 analysed participants, high quality evidence) and ranibizumab associated with laser was more effective than laser alone (4 studies on 919 participants, high quality evidence).Ocular severe adverse events, such as endophthalmitis, were rare in the included studies. Meta-analyses conducted for all antiangiogenic drugs compared with either sham or photocoagulation did not show a significant difference regarding serious systemic adverse events (15 studies, 441 events in 2985 participants, RR 0.98, 95% CI 0.83 to 1.17), arterial thromboembolic events (14 studies, 129 events in 3034 participants, RR 0.89, 95% CI 0.63 to 1.25) and overall mortality (63 events in 3562 participants, RR 0.88, 95% CI 0.52 to 1.47). We judged the quality of the evidence on adverse effects as moderate due to partial reporting of safety data and the exclusion of participants with previous cardiovascular events in some studies. AUTHORS' CONCLUSIONS: There is high quality evidence that antiangiogenic drugs provide a benefit compared to current therapeutic options for DMO, that is grid laser photocoagulation, in clinical trial populations at one or two years. Future research should investigate differences between drugs, effectiveness under real-world monitoring and treatment conditions, and safety in high-risk populations, particularly regarding cardiovascular risk

The prevention of implant surface alterations in the treatment of reri-implantitis: comparison of three different mechanical and physical treatments

The surgical treatment of peri-implantitis is currently based on the removal of biofilms from the implant surface by primary means of mechanical and physical treatments. However, such approaches often determine some alterations of the implant surface with detrimental effects on re-osseointegration. This study aims to evaluate the effects of four different mechanical and physical treatments on titanium samples with moderately rough surface. Air powder abrasion (AP) with glycine powder, a titanium brush (TB) and a diode laser at 3 W (L3) and 4 W (L4) were tested. Surface morphology, roughness and chemical composition were then assessed by scanning electron microscope (SEM), white light interferometer and X-ray photoelectron spectroscopy (XPS), respectively. The microscopic analysis revealed significant alterations in surface morphology on TB samples, while AP and L3 had only a minor or null impact. L4 samples revealed signs of overheating due to the excessive power. Nevertheless, the overall roughness of the samples was not significantly altered in terms of roughness parameters. Similarly, surface chemical composition was not significantly affected by the treatments. Among the treatments tested in this study, air powder abrasion with glycine powder and 3 W diode laser had the lowest impact on surface physicochemical properties.

Is there a place for nutritional supplements in the treatment of idiopathic male infertility?

Objective: Infertility affects 15% of couples in fertile age. Male factor is a cause of infertility in almost half of cases, mainly due to oligoasthenoteratozoospermia (OAT). The purpose of this study is to review the effects of nutritional supplements as medical treatment for idiopathic male infertility. Material and methods: A Pub Med and Medline review of the published studies utilizing nutritional supplements for the treatment of male infertility has been performed. Results: Clinical trials on Vitamin E, Vitamin A, Vitamin C. Arginine, Carnitine, N-Acetyl-Carnitine, Glutathione, Coenzyme Q10, Selenium and Zinc were reviewed. Although there is a wide variability in selected population, dose regimen and final outcomes, nutritional supplements both alone and in combination seems to be able to improve semen parameters (sperm count, sperm motility and morphology) and pregnancy rate in infertile men. Conclusions: There are rising evidences from published randomized trials and systematic review suggesting that nutritional supplementation may improve semen parameters and the likelihood of pregnancy in men affected by OAT. This improvement, however, is not consistent and there is a wide variation in the treatment regimens used. Well designed and adequately powered RCTs are needed to better clarify the role of nutritional supplements as treatment for male infertility

Modeling the thermal response of the retina during Indocyanine Green-assisted peeling of the internal limiting membrane

Previous works and surgical practices had shown that Indocyanine Green (ICG)-assisted peeling of the internal limiting membrane (ILM) in macular hole surgery may cause retinal damage. Different hypothesis were proposed in order to explain the induced damage. In this study the possibility of heat damage to the retina is investigated

DRY EYE: sindrome di Sjogren, analisi degli outcomes e correlazione con i parametri standard

INTRODUZIONE: la malattia dell’occhio secco (Dry Eye Disease(DED)) rappresenta una patologia di rilievo a causa dell’alta prevalenza, dell’impatto sulla qualità della vita e dei costi sociali e sanitari che ne derivano. Negli anni sono stati identificati iter diagnostici standardizzati comprendenti differenti test, nessuno dei quali può però essere considerato un gold-standard, in quanto non permettono di identificare segni o sintomi che correlano perfettamente al DED. SCOPO: studiare la correlazione fra markers di omeostasi della superficie oculare, le alterazioni strutturali rilevate alla microscopia confocale e i criteri usati nella diagnosi di SS, al fine di individuare nuovi potenziali markers diagnostici. PAZIENTI E METODI: 42 pazienti con pSS (40 donne e 2 uomini) sono stati sottoposti a Schirmer test I, TBUT, GLT e OSDI. Successivamente è stata eseguita l’analisi alla microscopia confocale in ognuno di loro, valutando per ogni paziente l’integrità dell’epitelio, la pachimetria, la densità cellulare dell’epitelio superficiale e basale e la tortuosità e riflettività delle fibre nervose. RISULTATI: nello studio delle correlazioni presenti fra i markers di omeostasi della superficie oculare e i parametri reumatologici risultano significative (p= 0,05) quelle fra TBUT e Schirmer e TBUT e GLT, oltre che OSDI e USFR. Fra i parametri analizzati al confocale invece la densità epiteliale dello strato basale risulta correlata a quella del superficiale e alla pachimetria (p= 0,05); l’integrità epiteliale è correlata positivamente alle alterazioni delle fibre nervose e negativamente alla densità cellulare dello strato superficiale. Esistono inoltre correlazioni con i parametri reumatologici: le alterazioni delle fibre nervose sono correlate con il FS (p= 0,05) e il numero di foci (p= 0,01), la pachimetria è correlata invece ai livelli di SSA (p=0,01). DISCUSSIONE: fra i risultati ottenuti la correlazione fra TBUT e test di Schirmer indica la natura mista della malattia nei pazienti con pSS, mentre quella con GLT testimonia il danno a carico dell’epitelio corneale e congiuntivale che si viene a creare in una condizione di instabilità del film lacrimale. Per quanto riguarda le correlazioni ottenute fra parametri analizzati alla microscopia confocale e quelli reumatologici, è interessante evidenziare il rapporto inverso fra la pachimetria e i livelli di SSA, ovvero la progressiva riduzione dello spessore corneale all’aumentare degli anticorpi in circolo. Oltre a questo, è rilevante anche la correlazione fra le alterazioni riguardanti le fibre nervose corneali, il FS e il numero di foci: questo risultato potrebbe indicare un collegamento fra la degenerazione nervosa a livello della cornea e il processo infiammatorio a carico delle ghiandole salivari, facendo ipotizzare un’analogia nella progressione della malattia a livello microscopico nelle due ghiandole. CONCLUSIONE: lo studio conferma l’utilizzo della microscopia confocale come strumento diagnostico aggiuntivo ai test tradizionali e indica una possibile nuova strada nell’analisi delle alterazioni microscopiche interessanti la ghiandola lacrimale, presumibilmente analoghe a quelle riguardanti le ghiandole salivari