Studies of p-type semiconductor photoelectrodes for tandem solar cells

Photoelectrodes and photovoltaic devices have been prepared via multiple thin film deposition methods. Aerosol assisted chemical vapour deposition (AACVD), electrodeposition (ED), chemical bath deposition (CBD) and doctor blade technique (DB) have been used to deposit binary and ternary metal oxide films on FTO glass substrates. The prepared thin films were characterised by a combination of SEM (Scanning Electron Microscopy), powder X-ray diffraction, mechanical strength tests and photochemical measurements. Nickel oxide (NiO) thin films prepared by AACVD were determined to have good mechanical strength . with a photocurrent of 7.6 μA cm-2 at 0 V and an onset potential of about 0.10 V. This contrasted with the dark current density of 0.3 μA cm-2 at 0 V. These NiO samples have very high porosity with crystalline columns evidenced by SEM. In comparison with the AACVD methodology, NiO films prepared using a combination of ED and DB show good mechanical strength but a higher photocurrent of 24 μA cm-2 at 0 V and an onset potential of about 0.10 V with a significantly greater dark current density of 7 μA cm-2 at 0 V. The characteristic features shown in the SEM are smaller pores compared to the AACVD method. Copper (II) oxide (CuO) and copper (I) oxide (Cu2O) films were fabricated by AACVD by varying the annealing temperature between 100-325°C in air using a fixed annealing time of 30 min. It was shown by photocurrent density (J-V) measurements that CuO produced at 325 °C was most stable and provided the highest photocurrent of 173 μA cm-2 at 0 V with an onset potential of about 0.23 V. The alignment of zinc oxide (ZnO) nano-rods and nano-tubes fabricated by CBD have been shown to be strongly affected by the seed layer on the FTO substrate. SEM images showed that AACVD provided the best seed layer for aligning the growth of the nano-rods perpendicular to the surface. Nano-rods were successfully altered into nano-tubes using a potassium chloride bath etching method. NiO prepared by both AACVD and the combined ED/DB method were sensitized to absorb more of the solar spectrum using AACVD to deposit CuO over the NiO. A large increase in the photocurrent was observed for the p-type photoelectrode. These p-type photoelectrode showed a photocurrent density of approximately 100 µA cm-2 at 0 V and an onset potential of 0.3 V. This photocathode was then used as a base to produce a solid state p-type solar cell. For the construction of the solid state solar cells several n-type semiconductors were used, these were ZnO, WO3 and BiVO4. WO3 and BiVO4 were successfully produced with BiVO4 proving to be the optimum choice. This cell was then studied more in depth and optimised by controlling the thickness of each layer and annealing temperatures. The best solid state solar cell produced had a Jsc of 0.541 μA cm-2 (541 nA) and a Voc of 0.14 V, TX146 made up of NiO 20 min, CuFe2O4 50 min, CuO 10 min, BiVO4 27 min, using AACVD and then annealed for 30 min at 600 °C

Relationship of parasite prevalence (a), uncomplicated episodes (b), severe episodes (c), and mortality (d) to annual average EIR by seasonality index (<i>φ</i>).

<p>Triangles represent simulated results. The lines show the estimated relationship between indicators from the simulation runs, fitted using fractional polynomial regression, for each pattern of seasonality as described by (the seasonality index , number of peaks) (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003812#pcbi-1003812-g001" target="_blank"><b>Figure 1</b></a>). Unbroken red line represents (0, 0). Brown dashed line represents (1,1). Orange dotted-dashed line represents (1,2). Green dotted line represents (2,1). Black dotted-dashed line represents (2,2). Blue dashed line represents (0.5, 2).</p

Relationship between the proportion of paediatric severe malaria in children under 1 year (a) and children aged 5–9 years (b) and parasite prevalence in the 2–10 age group from Okiro et. al, [18] (black circles) and OpenMalaria simulations (grey triangles).

<p>Triangles represent simulation results with (dark gray) and without (light gray) seasonality. Lines show the estimated relationships with (dashed) and without (unbroken) seasonality using fractional polynomial regression.</p

Relationship between mortality in children under 5 and average all-age parasite prevalence as described in Korenromp et. al [19] (black circles) and OpenMalaria simulations (triangles) for all deaths (light gray) and direct deaths only (dark gray).

<p>Lines show the simulation-based estimated relationships with seasonality ( = 2, 2 peaks) (dashed) and without seasonality (φ = 0, 0 peaks) (unbroken) using fractional polynomial regression. The observed values from Korenromp et. al are results of verbal autopsy which do not specify direct malaria deaths as opposed to indirect malaria deaths.</p

Median ages and inter-quartile range age prevalence curves in months of age by annual average EIR levels of <10 (a, d), 10–100 (b, e), and >100 (c, f), and seasonality patterns <i>φ</i> = 2, 2 peaks (a–c) and <i>φ</i> = 0, 0 peaks (d–f) for uncomplicated episodes, malaria hospitalizations, and mortality as observed in Carneiro et al. [6] (circles, unbroken lines) and simulated by the OpenMalaria model (triangles, dashed lines).

<p>Median ages and inter-quartile range age prevalence curves in months of age by annual average EIR levels of <10 (a, d), 10–100 (b, e), and >100 (c, f), and seasonality patterns <i>φ</i> = 2, 2 peaks (a–c) and <i>φ</i> = 0, 0 peaks (d–f) for uncomplicated episodes, malaria hospitalizations, and mortality as observed in Carneiro et al. <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003812#pcbi.1003812-Carneiro1" target="_blank">[6]</a> (circles, unbroken lines) and simulated by the OpenMalaria model (triangles, dashed lines).</p

Relationship of uncomplicated episodes (a), severe episodes (b), and mortality (c) to parasite prevalence by seasonality index.

<p>Triangles represent simulated results. The lines show the estimated relationship between indicators from the simulation runs, fitted using fractional polynomial regression, for each pattern of seasonality as described by (the seasonality index , number of peaks) (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003812#pcbi-1003812-g001" target="_blank"><b>Figure 1</b></a>). Unbroken red line represents (0, 0). Brown dashed line represents (1,1). Orange dotted-dashed line represents (1,2). Green dotted line represents (2,1). Black dotted-dashed line represents (2,2). Blue dashed line represents (0.5, 2).</p

Malaria indicators described in this study and their definitions for the purposes of this study.

<p>* Transformation used in fractional polynomial analysis.</p><p>Malaria indicators described in this study and their definitions for the purposes of this study.</p

MOESM1 of The time-course of protection of the RTS,S vaccine against malaria infections and clinical disease

Additional file 1: This file includes additional Figures of results that support and expand some of the results in the main text, but whose inclusion would detract from the main argument

Seasonality patterns of transmission observed malaria-endemic areas.

<p>Seasonality patterns of transmission observed malaria-endemic areas.</p

Relationship of severe episodes to uncomplicated episodes by seasonality index.

<p>Triangles represent simulated results. The lines show the estimated relationship between indicators from the simulation runs, fitted using fractional polynomial regression, for each pattern of seasonality as described by (the seasonality index , number of peaks) (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003812#pcbi-1003812-g001" target="_blank"><b>Figure 1</b></a>). Unbroken red line represents (0, 0). Brown dashed line represents (1,1). Orange dotted-dashed line represents (1,2). Green dotted line represents (2,1). Black dotted-dashed line represents (2,2). Blue dashed line represents (0.5, 2).</p