Engineering metal oxides for UV-stable perovskite solar cells

This thesis is a study of the role of the metal oxide electron transporting material in perovskite solar cells. The central research question is how the metal oxide influences the stability of perovskite solar cells and how the metal oxide can be modified to improve the stability. The thesis begins by providing four background chapters. Chapter 1 explains the need for solar energy and what perovskite solar cells can contribute to a clean energy future. Chapter 2 covers the working principles of solar cells, whereas Chapter 3 provides more detail about the history and architecture of the perovskite solar cell. Chapter 4 introduces the concept of nanostructuring metal oxides, using a block-copolymer template. The key experimental techniques and methods used throughout this work are described in Chapter 5. These introductory sections serve as the foundation for the four major experimental chapters of the thesis. Chapter 6 reports on the use of neodymium doped TiO2 in perovskite solar cells. Chapter 7 and Chapter 8 aim to increase the efficiency of SnO2 based perovskite solar cells, by making use of a novel electrode material and doping SnO2 with gallium. Chapter 9 covers the spontaneous coalescence of perovskite crystals, highlighting the extraordinary properties of perovskites.Diese Arbeit untersucht die Anwendung von Metalloxiden als Elektronentransportmaterial in Perowskit-Solarzellen. Die zentrale Forschungsfrage ist, wie Metalloxide die Stabilität von Perowskit-Solarzellen beeinflussen und wie Metalloxide, beispielsweise durch gezielte Dotierung, modifiziert werden können, um die Stabilität von Solarzellen zu verbessern. Die Arbeit beginnt mit vier einleitenden Hintergrundkapiteln. Kapitel 1 erklärt die zunehmende Notwendigkeit von Solarenergie und den Beitrag von Perowskit- Solarzellen zu einer sauberen Energiezukunft. Kapitel 2 stellt die Arbeitsprinzipien von Solarzellen vor, während Kapitel 3 mehr Details über die Geschichte und den Aufbau von Perowskit-Solarzellen enthält. Kapitel 4 leitet insbesondere das Konzept der Nanostrukturierung von Metalloxiden unter Verwendung einer Blockcopolymerschablone ein. Die für diese Arbeit benutzten experimentellen Methoden werden ausführlich in Kapitel 5 beschrieben. Diese einleitenden Kapitel dienen als Grundlage für die vier experimentellen Hauptkapitel dieser Arbeit. Kapitel 6 beschreibt die Verwendung von Neodymdotiertem TiO2 in Perowskit-Solarzellen und den Einfluss der Dotierung auf den Wirkungsgrad. Kapitel 7 und Kapitel 8 zielen darauf ab den Wirkungsgrad SnO2-basierter Perowskit-Solarzellen zu steigern, indem einerseits ein neuartiges Elektrodenmaterial verwendet wird und anderseits SnO2 mit Gallium dotiert wird. Kapitel 9 beschreibt die spontane Koaleszenz von kollidalen Perowskit-Kristallen, eine der aussergewöhnlichen Eigenschaften von Perowskitmaterialien

Critical Assessment of the Use of Excess Lead Iodide in Lead Halide Perovskite Solar Cells.

It is common practice in the lead halide perovskite solar cell field to add a small molar excess of lead iodide (PbI2) to the precursor solution to increase the device performance. However, recent reports have shown that an excess of PbI2 can accelerate performance loss. In addition, PbI2 is photoactive (band gap ∼2.3 eV), which may lead to parasitic absorption losses in a solar cell. Here we show that devices using small quantities of excess PbI2 exhibit better device performance as compared with stoichiometric devices, both initially and for the duration of a stability test under operating conditions, primarily by enhancing the charge extraction. However, the photolysis of PbI2 negates the beneficial effect on charge extraction by leaving voids in the perovskite film and introduces trap states that are detrimental for device performance. We propose that although excess PbI2 provides a good template for enhanced performance, the community must continue to seek other additives or synthesis routes that fulfill the same beneficial role as excess PbI2, but without the photolysis that negates these beneficial effects under long-term device operation

A Ga-doped SnO2 mesoporous contact for UV stable highly efficient perovskite solar cells

Increasing the stability of perovskite solar cells is a major challenge for commercialization. The highest efficiencies so far have been achieved in perovskite solar cells employing mesoporous TiO2 (m-TiO2). One of the major causes of performance loss in these m-TiO2-based perovskite solar cells is induced by UV- radiation. This UV instability can be solved by replacing TiO2 with SnO2; thus developing a mesoporous SnO2 (m-SnO2) perovskite solar cell is a promising approach to maximise efficiency and stability. However, the performance of mesoporous SnO2 (m-SnO2) perovskite solar cells has so far not been able to rival the performance of TiO2 based perovskite solar cells. In this study, for the first time, high-efficiency m-SnO2 perovskite solar cells are fabricated, by doping SnO2 with gallium, yielding devices that can compete with TiO2 based devices in terms of performance. We found that gallium doping severely decreases the trap state density in SnO2, leading to a lower recombination rate. This, in turn, leads to an increased open circuit potential and fill factor, yielding a stabilised power conversion efficiency of 16.4%. The importance of high-efficiency m-SnO2 based perovskite solar cells is underlined by stability data, showing a marked increase in stability under full solar spectrum illumination

A20 deficiency in lung epithelial cells protects against influenza A virus infection

A20 negatively regulates multiple inflammatory signalling pathways. We here addressed the role of A20 in club cells (also known as Clara cells) of the bronchial epithelium in their response to influenza A virus infection. Club cells provide a niche for influenza virus replication, but little is known about the functions of these cells in antiviral immunity. Using airway epithelial cell-specific A20 knockout (A20(AEC-KO)) mice, we show that A20 in club cells critically controls innate immune responses upon TNF or double stranded RNA stimulation. Surprisingly, A20(AEC-KO) mice are better protected against influenza A virus challenge than their wild type littermates. This phenotype is not due to decreased viral replication. Instead host innate and adaptive immune responses and lung damage are reduced in A20(AEC-KO) mice. These attenuated responses correlate with a dampened cytotoxic T cell (CTL) response at later stages during infection, indicating that A20(AEC-KO) mice are better equipped to tolerate Influenza A virus infection. Expression of the chemokine CCL2 (also named MCP-1) is particularly suppressed in the lungs of A20(AEC-KO) mice during later stages of infection. When A20(AEC-KO) mice were treated with recombinant CCL2 the protective effect was abrogated demonstrating the crucial contribution of this chemokine to the protection of A20(AEC-KO) mice to Influenza A virus infection. Taken together, we propose a mechanism of action by which A20 expression in club cells controls inflammation and antiviral CTL responses in response to influenza virus infection

Efficient room temperature aqueous Sb2S3 synthesis for inorganic-organic sensitized solar cells with 5.1% efficiencies.

Sb2S3 sensitized solar cells are a promising alternative to devices employing organic dyes. The manufacture of Sb2S3 absorber layers is however slow and cumbersome. Here, we report the modified aqueous chemical bath synthesis of Sb2S3 absorber layers for sensitized solar cells. Our method is based on the hydrolysis of SbCl3 to complex antimony ions decelerating the reaction at ambient conditions, in contrast to the usual low temperature deposition protocol. This simplified deposition route allows the manufacture of sensitized mesoporous-TiO2 solar cells with power conversion efficiencies up to η = 5.1%. Photothermal deflection spectroscopy shows that the sub-bandgap trap-state density is lower in Sb2S3 films deposited with this method, compared to standard deposition protocols.Cambridge Trust, the Mott Fund for Physics of the Environment and Corpus Christi College Cambridge for funding. A.S. acknowledges funding from the Engineering and Physical Sciences Research Council (EPSRC).This is the final version. It first appeared at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CC/c5cc01966d#!divAbstract

Substitution of lead with tin suppresses ionic transport in halide perovskite optoelectronics.

Despite the rapid rise in the performance of a variety of perovskite optoelectronic devices with vertical charge transport, the effects of ion migration remain a common and longstanding Achilles' heel limiting the long-term operational stability of lead halide perovskite devices. However, there is still limited understanding of the impact of tin (Sn) substitution on the ion dynamics of lead (Pb) halide perovskites. Here, we employ scan-rate-dependent current-voltage measurements on Pb and mixed Pb-Sn perovskite solar cells to show that short circuit current losses at lower scan rates, which can be traced to the presence of mobile ions, are present in both kinds of perovskites. To understand the kinetics of ion migration, we carry out scan-rate-dependent hysteresis analyses and temperature-dependent impedance spectroscopy measurements, which demonstrate suppressed ion migration in Pb-Sn devices compared to their Pb-only analogues. By linking these experimental observations to first-principles calculations on mixed Pb-Sn perovskites, we reveal the key role played by Sn vacancies in increasing the iodide ion migration barrier due to local structural distortions. These results highlight the beneficial effect of Sn substitution in mitigating undesirable ion migration in halide perovskites, with potential implications for future device development

Inflammatory monocytes regulate Th1 oriented immunity to CpG adjuvanted protein vaccines through production of IL-12

Due to their capacity to skew T cell responses towards Th1 oriented immunity, oligonucleotides containing unmethylated CpG motifs (CpG) have emerged as interesting adjuvants for vaccination. Whereas the signalling pathways in response to CpG mediated TLR9 activation have been extensively documented at the level of the individual cell, little is however known on the precise identity of the innate immune cells that govern T cell priming and polarisation to CpG adjuvanted protein antigens in vivo. In this study, we demonstrate that optimal induction of Th1 oriented immunity to CpG adjuvanted protein vaccines requires the coordinated actions of conventional DCs and of monocytes. Whilst conventional DCs were required for antigen presentation and initial T cell priming, monocytes constitute the main source of the Th1 polarising cytokine IL-12

Negen muzen, tien geboden. Historische en methodologische gevalstudies over de interactie tussen literatuur en ethiek

Literature traditionally holds a special place in society. This fact can be ascribed especially to literature’s unique capability to urge its audience and readers to allow a voice other than their own to resound within. And yet, literature’s role raises questions regarding one’s responsibility and engagement – questions that nearly every generation asks itself time and again with an ever changing urgency. Eight literary scholars from the research group ‘Literature – Ethics – Law’ (Ghent University) focus on this complex dialogue between literature and ethics. In the process, they arrive at answers that tease out crucial historical developments (from Plato to HIV/AIDS-prose), while also attending to the impact of methodological reevaluations during the search for such answers

Rapid Vapor-Phase Deposition of High-Mobility p-Type Buffer Layers on Perovskite Photovoltaics for Efficient Semi-Transparent Devices

Perovskite solar cells (PSCs) with transparent electrodes can be integrated with existing solar panels in tandem configurations to increase the power conversion efficiency. A critical layer in semi-transparent PSCs is the inorganic buffer layer, which protects the PSC against damage when the transparent electrode is sputtered on top. The development of n-i-p structured semi-transparent PSCs has been hampered by the lack of suitable p-type buffer layers. In this work we develop a p-type CuOx buffer layer, which can be grown uniformly over the perovskite device without damaging the perovskite or organic hole transport layer. The CuOx layer has high hole mobility (4.3 ± 2 cm2 V-1 s-1), high transmittance (>95%), and a suitable ionization potential for hole extraction (5.3 ± 0.2 eV). Semi-transparent PSCs with efficiencies up to 16.7% are achieved using the CuOx buffer layer. Our work demonstrates a new approach to integrate n-i-p structured PSCs into tandem configurations, as well as enable the development of other devices that need high quality, protective p-type layers.EPSRC Department Training Partnership studentship (No: EP/N509620/1), as well as Bill Welland. T.N.H. acknowledges funding from the EPSRC Centre for Doctoral Training in Graphene Technology (No. EP/L016087/1) and the Aziz Foundation. W.-W.L. and J.L.M.-D. acknowledge support from the EPSRC (Nos.: EP/L011700/1, EP/N004272/10), and the Isaac Newton Trust (Minute 13.38(k)). M.N. and J.L.M.-D. acknowledge financial support from EPSRC (No. EP/P027032/1). S. D. S. acknowledges support from the Royal Society and Tata Group (UF150033). R.L.Z.H. acknowledges support from the Royal Academy of Engineering under the Research Fellowship scheme (No.: RF\201718\1701), the Centre of Advanced Materials for Integrated Energy Systems (EPSRC Grant No. EP/P007767/1), the Isaac Newton Trust (Minute 19.07(d)), and the Kim and Juliana Silverman Research Fellowship at Downing College, Cambridge