We report the first experimental observation of a semiconductor/liquid junction whose open circuit voltage Voc is controlled by bulk diffusion/recombination processes. Variation in temperature, minority-carrier diffusion length, and/or in majority-carrier concentration produces changes in the Voc of the n-Si/CH3OH interface in accord with bulk recombination/diffusion theory. Under AM2 irradiation conditions, the extrapolated intercept at 0 K of Voc vs T plots yields activation energies for the dominant recombination process of 1.1–1.2 eV, in accord with the 1.12-eV band gap of Si. A crucial factor in achieving optimum performance of the n-Si/CH3OH interface is assigned to photoelectrochemical oxide formation, which passivates surface recombination sites at the n-Si/CH3OH interface and minimizes deleterious effects of pinning of the Fermi level at the Si/CH3OH junction. Controlled Si oxide growth, combined with optimization of bulk crystal parameters in accord with diffusion theory, is found to yield improved photoelectrode output parameters, with 12.0±1.5% AM2 efficiencies and AM1 Voc values of 632–640 mV for 0.2-Ω cm Si materials.
We thank Sullivan and Cruz for their thoughtful letter (1). They raise a very important point: an ignited strip of nitrocellulose is not a wildfire. The two systems differ in fuel, topography, and flame dynamics—to say nothing of scaling; direct links between them are difficult to draw. With this point, we agree completely.
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Abstract Context Polycystic ovary syndrome (PCOS) is associated with many traditional cardiovascular disease risk factors, but it is unclear whether PCOS is an independent risk factor for hypertension. Objective To investigate in a population-based setup whether PCOS associates with the risk of hypertension independently of body mass index (BMI) and with cardiovascular manifestations. Design Cross-sectional assessments in the Northern Finland Birth Cohort 1966 at ages 31 and 46 years. Setting General community. Participants Women who reported both oligo/amenorrhea and hirsutism at age 31 years and/or a diagnosis of PCOS by age 46 years [self-reported PCOS (srPCOS), n = 279] and women without PCOS symptoms or diagnosis (n = 1577). Intervention None. Main Outcome Measures Blood pressure (BP), BMI, and cardiovascular manifestations. Results Use of antihypertensive medication was significantly more common in women with srPCOS. At age 31 years, women with srPCOS had significantly higher systolic BP (SBP) and diastolic BP (DBP) than control women (SBP: normal weight: 119.9 ± 13.2 vs 116.9 ± 11.4 mm Hg, P = 0.017; overweight/obese: 126.1 ± 14.3 vs 123.0 ± 11.9 mm Hg, P = 0.031; and DBP: normal weight: 75.5 ± 10.0 vs 72.4 ± 9.6 mm Hg, P = 0.003; overweight/obese: 80.7 ± 11.8 vs 78.0 ± 10.6 mm Hg, P = 0.031). At age 46 years, srPCOS was significantly associated with hypertension (adjusted odds ratio = 1.56; 95% CI, 1.14 to 2.13) independently of BMI and with higher cardiovascular morbidity (6.8% vs 3.4%, P = 0.011). Hypertensive srPCOS displayed consistent, unfavorable changes in cardiac structure and function compared with controls. Conclusion Women with srPCOS displayed higher BP compared with controls already at early age and srPCOS was associated with hypertension independently of overweight/obesity. srPCOS was associated with increased cardiovascular morbidity in premenopausal women, suggesting that cardiovascular disease risk factors should be screened and efficiently managed early enough in women with PCOS.