Hidden polymorphism of FAPbI3 discovered by Raman spectroscopy

Formamidinium lead iodide FAPbI3 can be used in its cubic, black form as a light absorber material in single junction solar cells. It has a band gap 1.5 eV close to the maximum of the Shockley Queisser limit, and reveals a high absorption coefficient. Its high thermal stability up to 320 C has also a downside, which is the instability of the photo active form at room temperature RT . Thus, the black amp; 945; phase transforms at RT with time into a yellow non photo active amp; 948; phase. The black phase can be recovered by annealing of the yellow state. In this work, a polymorphism of the amp; 945; phase at room temperature was found as synthesized amp; 945;i , degraded amp; 945; amp; 948; and thermally recovered amp; 945;rec . They differ in the Raman spectra and PL signal, but not in the XRD patterns. Using temperature dependent Raman spectroscopy, we identified a structural change in the amp; 945;i polymorph at ca. 110 C. Above 110 C, the FAPbI3 structure has undoubtedly cubic Pm[3 with combining macron]m symmetry high temperature phase amp; 945;HT . Below that temperature, the amp; 945;i phase was suggested to have a distorted perovskite structure with Im[3 with combining macron] symmetry. Thermally recovered FAPbI3 amp; 945;rec also demonstrated the structural transition to amp; 945;HT at the same temperature ca. 110 C during its heating. The understanding of hybrid perovskites may bring additional assets in the development of new and stable structure

Unsettling planning theory

Recent political developments in many parts of the world seem likely to exacerbate rather than ameliorate the planetary-scale challenges of social polarization, inequality and environmental change societies face. In this unconventional multi-authored essay, we therefore seek to explore some of the ways in which planning theory might respond to the deeply unsettling times we live in. Taking the multiple, suggestive possibilities of the theme of unsettlement as a starting point, we aim to create space for reflection and debate about the state of the discipline and practice of planning theory, questioning what it means to produce knowledge capable of acting on the world today. Drawing on exchanges at a workshop attended by a group of emerging scholars in Portland, Oregon in late 2016, the essay begins with an introduction section exploring the contemporary resonances of ‘unsettling’ in, of and for planning theory. This is followed by four, individually authored responses which each connect the idea of unsettlement to key challenges and possible future directions. We end by calling for a reflective practice of theorizing that accepts unsettlement but seeks to act knowingly and compassionately on the uneven terrain that it creates

Deconstructing spatial planning: reinterpreting the articulation of a new ethos for English local planning

This article reviews recent debates about the emergence of “spatial planning” as a new ethos for English planning, suggesting that continued uncertainty around the term's use is partly caused by a failure to consider its emergence as the product of a contested political process. Drawing on an interpretive approach to policy analysis, the article goes on to show how this new organizing principle is a complex articulation of different and potentially contradictory reform impulses. The result is to destabilize the concept of spatial planning, showing how it has been constructed as an “empty signifier”, an unstable and tension-filled discursive stake in an ongoing politics of reform. Finally, it is argued that this has significant implications for the ways in which implementation success and failure should be understood and for analysis of planning reform initiatives and systems more widely

ALD Coated Mesoporous Iridium Titanium Mixed Oxides Maximizing Iridium Utilization for an Outstanding OER Performance

With the increasing production of renewable energy and concomitant depletion of fossil resources, the demand for efficient water splitting electrocatalysts continues to grow. Iridium Ir and iridium oxides IrOx are currently the most promising candidates for an efficient oxygen evolution reaction OER in acidic medium, which remains the bottleneck in water electrolysis. Yet, the extremely high costs for Ir hamper a widespread production of hydrogen H2 on an industrial scale. Herein, the authors report a concept for the synthesis of electrode coatings with template controlled mesoporosity surface modified with highly active Ir species. The improved utilization of noble metal species relies on the synthesis of soft templated metal oxide supports and a subsequent shape conformal deposition of Ir species via atomic layer deposition ALD at two different reaction temperatures. The study reveals that a minimum Ir content in the mesoporous titania based support is mandatory to provide a sufficient electrical bulk conductivity. After ALD, a significantly enhanced OER activity results in dependency of the ALD cycle number and temperature. The most active developed electrocatalyst film achieves an outstanding mass specific activity of 2622 mA mgIr 1 at 1.60 VRHE in a rotating disc electrode RDE setup at 25 C using 0.5 m H2SO4 as a supporting electrolyt

`China Design Now'

This article draws from cultural studies, political theory, international relations, art history and museum studies in order to consider `China Design Now' — the blockbuster exhibition, recently held at the V&A. It argues that, despite the inclusion of a number of interesting exhibits, the attempt to frame contemporary Chinese design independently of political contextualization has led to an exhibition which is largely unsatisfying. The approach taken by the V&A is further shown to have produced several ironic outcomes. First, by attempting to avoid `contentious' political issues, the museum has, in fact, forced the `political' to the fore. Second, by taking such an approach, the V&A demonstrates that it has failed to understand the essentially political nature of the design problem. Third, it has produced an exhibition which appears to advocate a (highly political) neoliberal agenda — one which insists on an inexorable drive towards greater global economic integration. Finally, it has failed to mention its own embeddedness within larger strategies of `cultural diplomacy' and the significance of such strategies for international relations and for cultural production. As well as drawing on a range of relevant literature, the article makes direct reference to exhibition wall texts, exhibit labels and quotations from the catalogue in order to support its argument

Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1 xGexS3 ternary alloys x 0 to 1 Homogeneous intermixing of Sn and Ge

Cu2Sn1 xGexS3 is a p type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto electronic properties. Seven single phase Cu2Sn1 xGexS3 films are prepared from x amp; 8239; amp; 8239;0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x amp; 8239; amp; 8239;0 to x amp; 8239; amp; 8239;1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 amp; 8239;eV with increasing Ge. The net acceptor density of all films is around 1018 amp; 8239;cm amp; 8722;3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structur

Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2Sn1-xGexS3 films are prepared from x = 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x = 0 to x = 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 1018 cm−3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure