L’Autre Forêt. La représentation de la forêt vierge africaine dans les relations de voyage de langue allemande du début du XXè siècle

International audienceLa forêt vierge, ou le Urwald, selon l'expression allemande, est un topos répandu dans la littérature et la fiction en général. Un voyage dans la forêt vierge symbolise souvent un voyage intérieur, dans les profondeurs de l'âme d'un personnage. La forêt vierge est alors « intériorisée », elle est métaphore des coins cachés et des régions inaccessibles du paysage intérieur. Le voyage de Marlow, dans le roman Heart of Darkness 1 de Joseph Conrad peut être considéré comme fondateur de ce double voyage. D'autres ont suivi l'exemple phare, comme par exemple Robert Müller avec Tropen 2 (1915), ou Max Frisch avec la scène clé d' Homo Faber 3 , ou encore Werner Herzog dans le film Fitzcarraldo 4. Enfin, Urs Widmer, dans Im Kongo 5 , livre une version ironique et actuelle du sujet conradien. Au cours de cette réflexion, je tenterai d'explorer ce lieu commun « Urwald » en m'attachant aux pas des voyageurs européens du début du XX è siècle. Mon but est de dégager certains éléments constitutifs du concept «Urwald » dans des relations de voyage, en partant du principe que ces documents constituent une sorte d'intermédiaire entre le factuel et le fictionnel. Dans une relation de voyage, l'auteur s'engage à dire la « vérité », il établit une sorte de pacte avec le lecteur, semblable au pacte autobiographique lejeunien. L'hypothèse de départ serait donc de savoir si l'on trouve dans ces relations de voyage des descriptions « véridiques » de la forêt vierge

The versatile SALSAC approach to heteroleptic copper(I) dye assembly in dye-sensitized solar cells

Surface-bound heteroleptic copper(I) dyes [Cu(L anchor )(L ancillary )] + are assembled using the 'surfaces-as-ligands, surfaces as complexes' (SALSAC) approach by three different procedures. The anchoring and ancillary ligands chosen are ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)-bis (4,1-phenylene))bis(phosphonic acid) ( 3 ) and 4,4'-bis(4-iodophenyl)-6,6'-diphenyl-2,2'-bipyridine ( 4 ), respectively. In the first SALSAC procedure, the FTO/TiO 2 electrode is functionalized with 3 in the first dye bath, and then undergoes ligand exchange with the homoleptic complex [Cu( 4 ) 2 ][PF 6 ] to give surface-bound [Cu( 3 )( 4 )] + . In the second method, the FTO/TiO 2 electrode functionalized with 3 is immersed in a solution containing a 1 : 1 mixture of [Cu(MeCN) 4 ][PF 6 ] and 4 to give surface-anchored [Cu( 3 )( 4 )] + . In the third procedure, the anchor 3 , copper(I) ion and ancillary ligand 4 are introduced in a sequential manner. The performances of the DSSCs show a dependence on the dye assembly procedure. The sequential method leads to the best-performing DSSCs with the highest values of J SC (7.85 and 7.73 mA cm –2 for fully masked cells) and overall efficiencies ( η = 2.81 and 2.71%, representing 41.1 and 39.6% relative to an N719 reference DSSC). Use of the 1 : 1 mixture of [Cu(MeCN) 4 ][PF 6 ] and 4 yields DSSCs with higher V OC values but lower J SC values compared to those assembled using the sequential approach; values of η are 2.27 and 2.29% versus 6.84% for the N719 reference DSSC. The ligand exchange procedure leads to DSSCs that perform relatively poorly. The investigation demonstrates the versatile and powerful nature of SALSAC in preparing dyes for copper-based DSSCs, allowing photoconversion efficiency of dye to be optimized for a given dye. The SALSAC strategy provides alternative hierarchical strategies where the isolation of the homoleptic [Cu(L ancillary ) 2 ] + is difficult or time-consuming; stepwise strategies are more atom-economic than ligand exchange involving the homoleptic [Cu(L ancillary ) 2 ] +

Europäische Gemeinsamkeiten und national- Kulturelle Spezifika des literarischen Blicks Auf Afrika: Möglichkeiten und Aporien des Vergleichs von Afrika-Reiseberichten

International audienceIm vorliegenden Beitrag wird der Frage nachgegangen, ob die Repräsentation von Afrikanerinnen und Afrikanern (im Folgenden wird das generische Maskulinum verwendet) in europäischen plurimedialen Reiseberichten der ersten Hälfte des 20. Jahrhunderts als eine gesamteuropäische bezeichnet werden kann oder ob es zur Ausformung national-kultureller Spezifika kommt. Den Ausgangspunkt der Untersuchung stellen Überlegungen von Jean-Marc Moura zu einer " culture coloniale européenne " dar. Er geht davon aus, dass man bei der Wahrnehmung Afrikas zu Beginn des 20. Jahrhunderts wohl von einer gesamteuropäischen Wahrnehmung sprechen könne, die sich im Großen und Ganzen als relativ homogen präsentiere: "Ces cadres demandent bien entendu à être précisés par l'examen de la spécificité des rythmes nationaux, mais les grandes structures entourant les évolutions particulières sont à chercher à l'échelle de ce que l'on pourrait presque appeler la culture coloniale européenne"

Catch the sun: new ancillary ligands in Copper(I) dye-sensitized solar cells lead to panchromatic light harvesting

The world population is increasing. More people demand better living conditions and the boom in the developing countries continues apace. The story of human progress is also the story of energy. Energy was and will be the key feature of progress. Nowadays, three energy transitions have taken place. These have developed our society from wood burning to coal-powered steam engines to a dependence on electricity which involved burning fossil fuels. All energy transitions up to now have included burning materials that produce not only energy but also air pollution and so-called greenhouse gases. The CO2 concentration in Earth's atmosphere is not at an acceptable level and the effects affect everyone on Earth. However, since the oil crisis in the 1970s and nuclear disasters such as Chernobyl and Fukushima, public awareness has been raised and the demand for alternative energy sources has increased. Renewable energy sources that disappeared over a long period, such as wind power, have made their comeback and a topical example of new renewable resources is photovoltaics. Photovoltaics produce renewable, sustainable and eco-friendly energy. Most commercial solar cells are based on silicon. Since their development in 1953, new generations of solar cells have been investigated in order to make them cheaper, more environmentally friendly and more efficient. Dye-sensitized solar cells are one cutting edge technology. They had their breakthrough in 1991 with the developments of Michael Grätzel and Brain O'Regan. A dye is adsorbed onto a semiconductor surface that is adhered to a conducting glass substrate. The electrical circuit is closed with a counter electrode and an electrolyte. Several types of dyes have been investigated but only a few have shown promising results. A new and exciting area encompasses copper(I)-based dyes. They consist of copper(I) complexes which incorporate a ligand with functional groups to anchor to the semiconductor surface and an ancillary ligand which can be structurally tuned to optimize light harvesting. Most of the ancillary ligands are based on a 2,2'-bipyridine core. Investigations aimed at improving cell performance had, in 2015, "got stuck" at photoconversions of around 2%. This thesis describes the path to new types of simple ancillary ligands that surpass the performance of the most optimized 2,2'-bipyridine-based ligands. The path includes the development of general methods that improve the economical part of the fabrication of the solar cells and the regeneration of destroyed dye. The new families of ancillary ligand lead to the development of panchromatic co-sensitized copper(I) dye-sensitized solar cells. For the first time, a copper(I) dye has been combined with a commercially available and cheap organic dye and the remarkable performance has shown the exciting potential of copper(I) dye-sensitized solar cells. Catch the Sun

The way to panchromatic copper(I)-based dye-sensitized solar cells: co-sensitization with the organic dye SQ2

We report the first example of n-type dye-sensitized solar cells (DSCs) co-sensitized with a copper(I)-based sensitizer and an organic dye. The heteroleptic copper(I) dye [Cu( 3 )( 1 )] + ( 3 = anchoring ligand ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)bis(4,1-phenylene))bis(phosphonic acid), 1 = ancillary ligand 2-(6-methylpyridin-2-yl)thiazole) was combined with the commercially available squaraine derivative SQ2 . By prudent matching of the external quantum efficiency (EQE) maxima arising from the two dyes in complementary parts of the visible spectrum, we have achieved the highest photoconversion efficiency reported for a copper-based DSC (65.6% relative to N719 set at 100%). This confirms the potential for the use of Earth-sustainable copper as the basis of sensitizers in DSCs. A combination of J–V measurements ( J = current density, V = voltage), EQE spectra and electrochemical impedance spectroscopy has been used to optimize and understand the effective use of the co-sensitized DSCs. We have shown that the sequences in which the photoanodes of the n-type DSCs are exposed to [Cu( 3 )( 1 )] + and SQ2 , and the times that the electrodes are immersed in the respective dye baths, critically influence the overall performance of the DSCs. A degree of aggregation of the SQ2 molecules on the electrode surface is important in terms of achieving panchromatic light-harvesting of the co-sensitized DSCs, but excessive aggregation is detrimenta

Exploring simple ancillary ligands in copper-based dye-sensitized solar cells: effects of a heteroatom switch and of co-sensitization

The copper( I ) complexes [Cu(1) 2 ][PF 6 ], [Cu(2) 2 ][PF 6 ], [Cu(3) 2 ][PF 6 ] and [Cu(4) 2 ][PF 6 ] (1 . 2-(1H-imidazol-2-yl)- 6-methylpyridine, 2 . 2-(6-methylpyridin-2-yl)oxazole, 3 . 2-(6-methylpyridin-2-yl)thiazole and 4 . 2- methyl-6-(1-methyl-1H-imidazol-2-yl)pyridine) are reported. The crystal structures of [Cu(2) 2 ][PF 6 ]$ 0.5CH 2 Cl 2 and [Cu(3) 2 ][PF 6 ] confirm N,N 0 -chelation modes for 2 and 3, and tetrahedral copper( I ). In the solution absorption spectra, the MLCT band shifts to lower energy with a change in heteroatom (O, 424 nm; NH, 435 nm; NMe, 446 nm; S, 465 nm). [Cu(1) 2 ][PF 6 ] and [Cu(4) 2 ][PF 6 ] undergo copper-centred oxidative processes at lower potential than the complexes with O or S heteroatoms. Heteroleptic complexes [Cu(5)(L)] + (5 . ((6,6 0 -dimethyl-[2,2 0 -bipyridine]-4,4 0 -diyl)bis(4,1-phenylene)bis(phosphonic acid)), L . 1–4) were assembled on FTO/TiO 2 electrodes. The shift in the MLCT band (O NH < NMe < S) in the solid-state absorption spectra of the dye-functionalized electrodes parallels that of solution. The photoconversion efficiencies (h) of masked, dye-sensitized solar cells (DSCs) containing [Cu(5)(L)] + (L . 1– 4) dyes and an I/I 3 redox shuttle follow the order [Cu(5)(1)] + (3.03%) > [Cu(5)(3)] + (2.88%) > [Cu(5)(4)] + (2.71%) > [Cu(5)(2)] + (2.62%) relative to 7.55% for N719. Ancillary ligand 1 (with NH) leads to the highest open-circuit voltage (V OC . 608 mV) whilst 3 (S-heteroatom) gives the highest short-circuit current density (J SC . 7.76 mA cm 2 ). The performances of [Cu(5)(1)] + and [Cu(5)(3)] + are understood with the aid of electrochemical impedance spectroscopy (EIS). The DSC with [Cu(5)(1)] + exhibits a high chemical capacitance (C m ) and a low recombination resistance (R rec ); since the latter is offset by a low transport resistance (R tr ), a high J SC and V OC are observed for [Cu(5)(1)] + . DSCs with [Cu(5)(3)] + have the lowest R tr of all four devices. The performance of DSCs sensitized by a combination of [Cu(5)(1)] + and [Cu(5)(3)] + were assessed in order to capitalize upon the high V OC of [Cu(5)(1)] + and the high J SC of [Cu(5)(3)] + . After FTO/ TiO 2 functionalization with anchor 5, the electrodes were treated with a 1 : 1 mix of [Cu(5)(1)] + and [Cu(5)(3)] + or sequentially with [Cu(5)(3)] + then [Cu(5)(1)] + , or [Cu(5)(1)] + then [Cu(5)(3)] + . The DSC performances and the EIS parameters are consistent with competition between 1 and 3 for surface binding-sites; 1 dominates over 3, both in binding and in contribution to the overall photoresponse

Cuprophilia: dye-sensitized solar cells with copper(I) dyes and copper(I)/(II) redox shuttles

With a goal of designing dye-sensitized solar cells (DSCs) containing only Earthabundant components to achieve sustainable energy conversion, DSCs with heteroleptic copper(I)-based dyes and homoleptic copper(I)/(II) redox shuttles have been investigated. By using a phosphonic acid anchor, and 4,4'-dimethoxy-6,6'- dimethyl-2,2'-bipyridine as the ancillary ligand in the dye and in the electrolyte, a DSC photoconversion efficiency of 2.06% (38.1% relative to N719 set at 100%) was achieved. The results demonstrate the potential for all-copper-based DSCs, opening the way for further dye and electrolyte optimization

The influence of phosphonic acid protonation state on the efficiency of bis(diimine)copper(I) dye-sensitized solar cells

We present an investigation of the effects of a change in the protonation state of the phosphonic acid anchoring ligand in the dye [Cu(H 4 1 )( 2 )][PF 6 ] (H 4 1 = ((6,6'-dimethyl-[2,2'-bipyridine]-4,4'-diyl)bis(4,1-phenylene))bis(phosphonic acid), 2 = 4,4'-bis(4-bromophenyl)-6,6'-dimethyl-2,2'-bipyridine) on the performance of n-type dye-sensitized solar cells (DSCs). FTO/TiO 2 electrodes were immersed in solutions of H 4 1 in the presence of base (0–4 equivalents). TiO 2 -anchored heteroleptic copper(I) sensitizers were subsequently formed by ligand exchange between the homoleptic complex [Cu( 2 ) 2 ][PF 6 ] and the anchored ligand [H 4– n 1 ] n – . The results demonstrate that the addition of one equivalent of base during the initial surface functionalization can afford up to a 26% increase in DSC efficiency, while the addition of ≥3 equivalents of base significantly hinders DSC performance. Deprotonation of H 4 1 has been investigated using 1 H and 31 P NMR spectroscopic titrations. Further insight into DSC performance has been gained by using electrochemical impedance spectroscopy, and a comparison is made between DSCs in which the working electrodes are either pre-treated with a base, or exposed to a base post heteroleptic copper(I) dye-assembly

Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells

A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-centred transitions) which are red-shifted on going from X = H to X = I, and a broad metal-to-ligand charge transfer band with λmax in the range 387–395 nm. The ten complexes are yellow emitters in solution and yellow or yellow-orange emitters in the solid-state. For a given N^N ligand, the solution photoluminescence (PL) spectra show no significant change on going from [Cu(N^N)(POP)]+ to [Cu(N^N)(xantphos)]+; introducing the iodo-functionality into the N^N domain leads to a red-shift in λmaxem compared to the complexes with the benchmark N^N ligand 5. In the solid state, [Cu(1)(POP)][PF6] and [Cu(1)(xantphos)][PF6] (fluoro-substituent) exhibit the highest PL quantum yields (74 and 25%, respectively) with values of τ1/2 = 11.1 and 5.8 μs, respectively. Light-emitting electrochemical cells (LECs) with [Cu(N^N)(P^P)][PF6] complexes in the emissive layer have been tested. Using a block-wave pulsed current driving mode, the best performing device employed [Cu(1)(xantphos)]+ and this showed a maximum luminance (Lummax) of 129 cd m−2 and a device lifetime (t1/2) of 54 h; however, the turn-on time (time to reach Lummax) was 4.1 h. Trends in performance data reveal that the introduction of fluoro-groups is beneficial, but that the incorporation of heavier halo-substituents leads to poor devices, probably due to a detrimental effect on charge transport; LECs with the iodo-functionalized N^N ligand 4 failed to show any electroluminescence after 50 h

What difference does a thiophene make? Evaluation of a 4,4′-bis(thiophene) functionalised 2,2′-bipyridyl copper(I) complex in a dye-sensitized solar cell

AbstractThe synthesis of a 4,4′-bis(2-thienyl-5-carboxylic acid) functionalised 2,2′-bipyridine ligand and corresponding copper(I) complex is described and its application in a dye-sensitized solar cell (DSSC) is studied. The positioning of the thiophene groups appears favourable from DFT analysis and a best efficiency of 1.41% was obtained with this dye, for a 0.3 cm2 cell area DSSC. Two absorbance bands are observed in the electronic absorption spectrum of the copper(I) complex at 316 nm and 506 nm, with ε values of 50,000 M−1 cm−1 and 9030 M−1 cm−1, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy are also used to provide a detailed analysis of the dye and assess its functionality in a DSSC