Controlling hole extraction in organic photovoltaics

The work in this thesis focuses on the process of hole extraction in OPVs both in terms of the development of new hole extracting materials and understanding the factors that determine the efficiency of hole extraction to enable the intelligent design of these electrodes. In Chapter 1 an overview of organic semiconductors and organic photovoltaic (OPV) devices is given including details of the fundamental processes that underpin the operation of OPVs. In Chapter 2 an overview of the experimental techniques used in this thesis is presented. Chapter 3 reports the use of surface oxidised Au nanoparticles (AuNPs) as an efficient hole-extracting material in molecular OPVs. This class of hole-extracting material is unusual in that it is remarkably effective even at low surface coverage and offers the advantage over conventional hole-extracting materials of solution processing from a pH neutral solution. The effectiveness of oxidised AuNPs as a hole extracting material is attributed to the very high work function of these particles and geometric electric field enhancement effects. Chapters 4 and 5 describe experiments designed to determine how nanoscale geometric electric field enhancement and electrode work function affects the efficiency of hole-extraction in OPVs, respectively. From these latter chapters generic electrode design rules are proposed. Finally, in Chapter 6 an overview of future work is given. With the exception of the final part of Chapter 5, the results of chapters 3, 4 and 5 have been published in peer reviewed scientific journals

Direct versus indirect H atom elimination from photoexcited phenol molecules

The active role of the optically dark pi sigma* state, following UV absorption, has been implicated in the photochemistry of a number of biomolecules. This work focuses on the role of the pi sigma* state in the photochemistry of phenol upon excitation at 200 nm. By probing the neutral hydrogen following UV excitation, we show that hydrogen elimination along the dissociative pi sigma* potential energy surface occurs within 103 30 fs, indicating efficient coupling at the S-1/S-2 and S-0/S-2 conical intersections, with no identifiable role of statistical unimolecular decay of vibronically excited (SO) phenol in the timeframe of our measurements

Enhancing the open-circuit voltage of molecular photovoltaics using oxidized au nanocrystals

For organic photovoltaics (OPV) to realize applications effective strategies to maximize the open-circuit voltage must be developed. Herein we show that solution-processed surface-oxidized Au nanoctystals (o-AuNC) dramatically increase the open-circuit voltage (V-oc) of OPV cells based on boron-subphthalocyanine chloride (SubPc)/C-60 and chloro-aluminum phthalocyanine (CIAIPc)/C-60 heterojunctions when incorporated at the interface between the hole-extracting electrode and the phthalocyanine donor layer. In addition, the cell-to-cell variation in V-oc is reduced by up to 10-fold combined with a large reduction in the light intensity dependence of V-oc, both of which are important advantages for practical application. The largest increase in V-oc is achieved for SubPc/C-60-based cells which exhibit a 45% increase to 1.09 +/- 0.01 V-an exceptionally high value for a single junction small molecule OPV. Remarkably these improvements are achieved using submonolayers of o-AuNC, which can be rationalized in terms of the exceptionally high work function of o-AuNC (similar to 5.9 eV) and geometric electric field enhancement effects

Nanoscale geometric electric field enhancement in organic photovoltaics

Generic design rules for electrode–organic semiconductor contacts that transcend specific materials are urgently required to guide the development of new electrodes and provide a framework for engineering this important class of interface. Herein a novel nanostructured window electrode is utilized in conjunction with three-dimensional electrostatic modeling to elucidate the importance of geometric electric field enhancement effects at the electrode interfaces in organic photovoltaics. The results of this study show that nanoscale protrusions at the electrode surfaces in organic photovoltaics dramatically improve the efficiency of photogenerated charge carrier extraction to the external circuit and that the origin of this improvement is the local amplification of the electrostatic field in the vicinity of said protrusions. This wholly geometric approach to engineering electrodes at the nanoscale is materials generic and can be employed to enhance the efficiency of charge carrier injection or extraction in a wide range of organic electronic devices

Prospective observational cohort study on grading the severity of postoperative complications in global surgery research

Background The Clavien–Dindo classification is perhaps the most widely used approach for reporting postoperative complications in clinical trials. This system classifies complication severity by the treatment provided. However, it is unclear whether the Clavien–Dindo system can be used internationally in studies across differing healthcare systems in high- (HICs) and low- and middle-income countries (LMICs). Methods This was a secondary analysis of the International Surgical Outcomes Study (ISOS), a prospective observational cohort study of elective surgery in adults. Data collection occurred over a 7-day period. Severity of complications was graded using Clavien–Dindo and the simpler ISOS grading (mild, moderate or severe, based on guided investigator judgement). Severity grading was compared using the intraclass correlation coefficient (ICC). Data are presented as frequencies and ICC values (with 95 per cent c.i.). The analysis was stratified by income status of the country, comparing HICs with LMICs. Results A total of 44 814 patients were recruited from 474 hospitals in 27 countries (19 HICs and 8 LMICs). Some 7508 patients (16·8 per cent) experienced at least one postoperative complication, equivalent to 11 664 complications in total. Using the ISOS classification, 5504 of 11 664 complications (47·2 per cent) were graded as mild, 4244 (36·4 per cent) as moderate and 1916 (16·4 per cent) as severe. Using Clavien–Dindo, 6781 of 11 664 complications (58·1 per cent) were graded as I or II, 1740 (14·9 per cent) as III, 2408 (20·6 per cent) as IV and 735 (6·3 per cent) as V. Agreement between classification systems was poor overall (ICC 0·41, 95 per cent c.i. 0·20 to 0·55), and in LMICs (ICC 0·23, 0·05 to 0·38) and HICs (ICC 0·46, 0·25 to 0·59). Conclusion Caution is recommended when using a treatment approach to grade complications in global surgery studies, as this may introduce bias unintentionally

The surgical safety checklist and patient outcomes after surgery: a prospective observational cohort study, systematic review and meta-analysis

© 2017 British Journal of Anaesthesia Background: The surgical safety checklist is widely used to improve the quality of perioperative care. However, clinicians continue to debate the clinical effectiveness of this tool. Methods: Prospective analysis of data from the International Surgical Outcomes Study (ISOS), an international observational study of elective in-patient surgery, accompanied by a systematic review and meta-analysis of published literature. The exposure was surgical safety checklist use. The primary outcome was in-hospital mortality and the secondary outcome was postoperative complications. In the ISOS cohort, a multivariable multi-level generalized linear model was used to test associations. To further contextualise these findings, we included the results from the ISOS cohort in a meta-analysis. Results are reported as odds ratios (OR) with 95% confidence intervals. Results: We included 44 814 patients from 497 hospitals in 27 countries in the ISOS analysis. There were 40 245 (89.8%) patients exposed to the checklist, whilst 7508 (16.8%) sustained ≥1 postoperative complications and 207 (0.5%) died before hospital discharge. Checklist exposure was associated with reduced mortality [odds ratio (OR) 0.49 (0.32–0.77); P\u3c0.01], but no difference in complication rates [OR 1.02 (0.88–1.19); P=0.75]. In a systematic review, we screened 3732 records and identified 11 eligible studies of 453 292 patients including the ISOS cohort. Checklist exposure was associated with both reduced postoperative mortality [OR 0.75 (0.62–0.92); P\u3c0.01; I2=87%] and reduced complication rates [OR 0.73 (0.61–0.88); P\u3c0.01; I2=89%). Conclusions: Patients exposed to a surgical safety checklist experience better postoperative outcomes, but this could simply reflect wider quality of care in hospitals where checklist use is routine

Critical care admission following elective surgery was not associated with survival benefit:prospective analysis of data from 27 countries

Purpose: As global initiatives increase patient access to surgical treatments, there is a need to define optimal levels of perioperative care. Our aim was to describe the relationship between the provision and use of critical care resources and postoperative mortality. Methods: Planned analysis of data collected during an international 7-day cohort study of adults undergoing elective in-patient surgery. We used risk-adjusted mixed-effects logistic regression models to evaluate the association between admission to critical care immediately after surgery and in-hospital mortality. We evaluated hospital-level associations between mortality and critical care admission immediately after surgery, critical care admission to treat life-threatening complications, and hospital provision of critical care beds. We evaluated the effect of national income using interaction tests. Results: 44,814 patients from 474 hospitals in 27 countries were available for analysis. Death was more frequent amongst patients admitted directly to critical care after surgery (critical care: 103/4317 patients [2%], standard ward: 99/39,566 patients [0.3%]; adjusted OR 3.01 [2.10–5.21]; p < 0.001). This association may differ with national income (high income countries OR 2.50 vs. low and middle income countries OR 4.68; p = 0.07). At hospital level, there was no association between mortality and critical care admission directly after surgery (p = 0.26), critical care admission to treat complications (p = 0.33), or provision of critical care beds (p = 0.70). Findings of the hospital-level analyses were not affected by national income status. A sensitivity analysis including only high-risk patients yielded similar findings. Conclusions: We did not identify any survival benefit from critical care admission following surgery

Incidence of severe critical events in paediatric anaesthesia (APRICOT): a prospective multicentre observational study in 261 hospitals in Europe

Background Little is known about the incidence of severe critical events in children undergoing general anaesthesia in Europe. We aimed to identify the incidence, nature, and outcome of severe critical events in children undergoing anaesthesia, and the associated potential risk factors. Methods The APRICOT study was a prospective observational multicentre cohort study of children from birth to 15 years of age undergoing elective or urgent anaesthesia for diagnostic or surgical procedures. Children were eligible for inclusion during a 2-week period determined prospectively by each centre. There were 261 participating centres across 33 European countries. The primary endpoint was the occurence of perioperative severe critical events requiring immediate intervention. A severe critical event was defined as the occurrence of respiratory, cardiac, allergic, or neurological complications requiring immediate intervention and that led (or could have led) to major disability or death. This study is registered with ClinicalTrials.gov, number NCT01878760. Findings Between April 1, 2014, and Jan 31, 2015, 31â127 anaesthetic procedures in 30â874 children with a mean age of 6·35 years (SD 4·50) were included. The incidence of perioperative severe critical events was 5·2% (95% CI 5·0â5·5) with an incidence of respiratory critical events of 3·1% (2·9â3·3). Cardiovascular instability occurred in 1·9% (1·7â2·1), with an immediate poor outcome in 5·4% (3·7â7·5) of these cases. The all-cause 30-day in-hospital mortality rate was 10 in 10â000. This was independent of type of anaesthesia. Age (relative risk 0·88, 95% CI 0·86â0·90; p<0·0001), medical history, and physical condition (1·60, 1·40â1·82; p<0·0001) were the major risk factors for a serious critical event. Multivariate analysis revealed evidence for the beneficial effect of years of experience of the most senior anaesthesia team member (0·99, 0·981â0·997; p<0·0048 for respiratory critical events, and 0·98, 0·97â0·99; p=0·0039 for cardiovascular critical events), rather than the type of health institution or providers. Interpretation This study highlights a relatively high rate of severe critical events during the anaesthesia management of children for surgical or diagnostic procedures in Europe, and a large variability in the practice of paediatric anaesthesia. These findings are substantial enough to warrant attention from national, regional, and specialist societies to target education of anaesthesiologists and their teams and implement strategies for quality improvement in paediatric anaesthesia. Funding European Society of Anaesthesiology