Search

Metal halide perovskites (MHPs) have shown an incredible rise in efficiency, reaching as high as 25.7%, which now competes with traditional photovoltaic technologies. Herein, we excluded CsX and RbX, the most commonly used cations to stabilize FAPbI3, from the bulk of perovskite thin films and applied them on the surface, as passivation agents. Extensive device optimization led to a power conversion efficiency (PCE) of 24.1% with a high fill factor (FF) of 82.2% upon passivation with CsI. We investigated in-depth the effect of CsI passivation on structural and optoelectronic properties using X-ray diffraction (XRD), angle resolved X-ray photoelectron spectroscopy (ARXPS), Kelvin Probe Force (KPFM) microscopy, time-resolved photoluminescence (TRPL), photoluminescence quantum yield (PLQY) and electroabsorption spectroscopy (TREAS). Furthermore, passivated devices exhibit enhanced operational stability, with optimized passivation with CsI leading to a retention of ~90% of initial PCE under 1 Sun illumination with maximum power point tracking for 600 h., Comment: 27 pages, 19 figures

Electrochemical CO2 reduction driven by renewable electricity is one of the promising strategies to store sustainable energy as fuels. However, the selectivity of value-added multi-carbon products remains poor for further application of this process. Here, we regulate CO adsorption by forming a Nafion layer on the copper (Cu) electrode that is repulsive to OH−, contributing to enhanced selectivity of CO2 reduction to C2+ products with the suppression of C1 products. The operando Raman spectroscopy indicates that the local OH− would adsorb on part of active sites and decrease the adsorption of CO. Therefore, the electrode with repulsive to OH− can adjust the concentration of OH−, leading to the increased adsorption of CO and enhanced C–C coupling. This work shows that electrode design could be an effective strategy for improving the selectivity of CO2 reduction to multi-carbon products.

Understanding the kinetics and energetics of metal halide perovskite formation, particularly from the structural point of view at the nano-regime, is important for the advancement of perovskite devices. Rational insights are needed regarding the mechanism by which perovskite conversion reactions occurs and their kinetics. Here we examine the structural evolution of precursor and perovskite phase using in situ synchrotron x-ray scattering. This approach mitigates issues associated with illumination and electron beam-based techniques and allows fundamental conclusions to be drawn regarding the kinetics of these reactions. We find that kinetics and the orientation of grains strongly depend on both the lead halide framework and the nature of the A-cation, with fastest kinetics for MAPbI3, followed by FAPbI3, and slowest for MAPbBr3. Molecular dynamics simulations and density functional theory calculations further reveal that these reactions are diffusion-controlled with a hopping time of 5-400 s, corroborating experimental results while adding new dimensions to conversion reactions.

In this study, we report the effects of co-catalysts of Pt nanoparticles and Fe3O4 clusters on photocatalytic behaviors of g-C3N4 (CN) and the use of the resulting photocatalyst for CO2 photoreduction to solar fuels in a flow reactor operated at room-temperature. In presence of H2O vapors, the selectivity of photogenerated electrons was emphasized, and found that the yield rate and selectivity of CH4 were improved by deposition of Pt on CN. With further inclusion of Fe3O4 over Pt/g-C3N4 (PtCN), the CH4 yield rate was significantly enhanced and H2 formation inhibited simultaneously, resulting in improved CH4 selectivity. Results show that the optimized Fe3O4/ Pt co-decorated CN (0.50 %FPtCN) heterostructure possesses significantly enhanced CO and CH4 yield rates of 1.83 mu molg- 1h- 1 and 0.532 mu molg- 1h- 1, respectively, which were 9 and 38 times superior to pure CN, attributed predominantly synergistic effects of Pt, Fe3O4, and CN. Owing to exceptional conductivity and electron-sink function, Pt NPs are an excellent electron transporter, which facilitates interfacial charges transfer and prohibits their recombination, while, the Fe3O4 clusters can synergistically promote the CO2 photoreduction by effectively using electrons as the oxidation - reduction center. Finally, insight obtained from results is used to propose a possible underlying mechanism for superior photocatalytic performance.

Perovskite solar cells (PSCs) have become the representatives of next generation of photovoltaics; nevertheless, their stability is insufficient for large scale deployment, particularly the reverse bias stability. Here, we propose a transparent conducting oxide (TCO) and low-cost metal composite electrode to improve the stability of PSCs without sacrificing the efficiency. The TCO can block ion migrations and chemical reactions between the metal and perovskite, while the metal greatly enhances the conductivity of the composite electrode. As a result, composite electrode-PSCs achieved a power conversion efficiency (PCE) of 23.7% (certified 23.2%) and exhibited excellent stability, maintaining 95% of the initial PCE when applying a reverse bias of 4.0 V for 60 s and over 92% of the initial PCE after 1000 h continuous light soaking. This composite electrode strategy can be extended to different combinations of TCOs and metals. It opens a new avenue for improving the stability of PSCs.

All-inorganic perovskite films hold promise for improving the stability of perovskite solar cells (PSCs). However, the 3D alpha phase of narrow-bandgap inorganic perovskites is thermodynamically unstable at room temperature, limiting the development of high-performance inorganic PSCs. Here, we show that europium doping of CsPbI2Br stabilizes the alpha phase of this inorganic perovskite at room temperature. We rationalize it by using solid-state nuclear magnetic resonance and high-angle annular dark-field scanning transmission electron microscopy, which show that europium is incorporated into the perovskite lattice. We demonstrate amaximum power-conversion efficiency of 13.71% for an inorganic PSC with the CsPb0.95Eu0.05I2Br perovskite and alpha stable power output of 13.34%. Using electroluminescence we show that incorporation of europium reduces non-radiative recombination, resulting in high open-circuit voltage of 1.27 V. The devices retain 93% of the initial efficiency after 370 hr under 100 mW cm(-2) continuous white light illumination under maximum-power point-tracking measurement.

Today's perovskite solar cells (PSCs) mostly use components, such as organic hole conductors or noble metal back contacts, that are very expensive or cause degradation of their photovoltaic performance. For future large-scale deployment of PSCs, these components need to be replaced with cost-effective and robust ones that maintain high efficiency while ascertaining long-term operational stability. Here, a simple and low-cost PSC architecture employing dopant-free TiO2 and CuSCN as the electron and hole conductor, respectively, is introduced while a graphitic carbon layer deposited at room temperature serves as the back electrical contact. The resulting PSCs show efficiencies exceeding 18% under standard AM 1.5 solar illumination and retain approximate to 95% of their initial efficiencies for >2000 h at the maximum power point under full-sun illumination at 60 degrees C. In addition, the CuSCN/carbon-based PSCs exhibit remarkable stability under ultraviolet irradiance for >1000 h while under similar conditions, the standard spiro-MeOTAD/Au based devices degrade severely.

Efficiencies >20% are obtained from the perovskite solar cells (PSCs) employing Cs+ and Rb+ based perovskite compositions; therefore, it is important to understand the effect of these inorganic cations specifically Rb+ on the properties of perovskite structures. Here the influence of Cs+ and Rb+ is elucidated on the structural, morphological, and photophysical properties of perovskite structures and the photovoltaic performances of resulting PSCs. Structural, photoluminescence (PL), and external quantum efficiency studies establish the incorporation of Cs+ (x < 10%) but amply rule out the possibility of Rb-incorporation into the MAPbI(3) (MA = CH3NH3+) lattice. Moreover, morphological studies and time-resolved PL show that both Cs+ and Rb+ detrimentally affect the surface coverage of MAPbI(3) layers and charge-carrier dynamics, respectively, by influencing nucleation density and by inducing nonradiative recombination. In addition, differential scanning calorimetry shows that the transition from orthorhombic to tetragonal phase occurring around 160 K requires more thermal energy for the Cs-containing MAPbI(3) systems compared to the pristine MAPbI(3). Investigation including mixed halide (I/Br) and mixed cation A-cation based compositions further confirms the absence of Rb+ from the 3D-perovskite lattice. The fundamental insights gained through this work will be of great significance to further understand highly promising perovskite compositions.

Given the limitations of the materials available for photoelectrochemical water splitting, a multiphoton (tandem) approach is required to convert solar energy into hydrogen efficiently and durably. Here we investigate a promising system consisting of a hematite photoanode in combination with dye-sensitized solar cells with newly developed organic dyes, such as the squaraine dye, which permit new configurations of this tandem system. Three configurations were investigated: two side-by-side dye cells behind a semitransparent hematite photoanode, two semitransparent dye sensitized solar cells (DSCs) in front of the hematite, and a trilevel hematite/DSC/DSC architecture. Based on the current-voltage curves of state-of-the-art devices made in our laboratories, we found the trilevel tandem architecture (hematite/SQ1 dye/N749 dye) produces the highest operating current density and thus the highest expected solar-to-hydrogen efficiency (1.36% compared with 1.16% with the standard back DSC case and 0.76% for the front DSC case). Further investigation into the wavelength-dependent quantum efficiency of each component revealed that in each case photons lost as a result of scattering and reflection reduce the performance from the expected 3.3% based on the nanostructured hematite photoanodes. We further suggest avenues for the improvement of each configuration from both the DSC and the photoanode parts.

The surge of the power conversion efficiency of metal halide lead perovskite solar cells comes with concerns, such as the long-term ecotoxicity of lead compounds, their sensitivity toward moisture and oxygen, or the scarcity of some of their components. Most perovskite solar cells still suffer from serious stability problems when measured under real working conditions (maximum power point tracking at 60 degrees C). In the long run, stability will certainly decide on the fate of CH3NH3PbI3 and related lead perovskites for their use in photovoltaic modules. Herein, we show an effective and inexpensive strategy to perform ageing of perovskite solar cells under maximum power point tracking. For the first time, we analyze the issue of power extraction from solar cells exhibiting hysteresis. We show that a standard tracking algorithm such as perturb and observe fails to converge to the maximum power point of the solar cell if it exhibits j(V) hysteresis, and we present an effective strategy to stabilize the algorithm. We show that enforcing oscillations in forward bias can boost the mean power output of some perovskite solar cells by more than 10%, in contrast to a reference crystalline silicon solar cell. Copyright (c) 2017 John Wiley & Sons, Ltd.

Electron transfers (ET) between a donor (D) and an acceptor (A) through a molecular bridge (B) are of great importance in biological systems, molecular electronics and molecular based light-energy conversion systems. Here, the back and the forward electron transfer rates have been measured by femtosecond and nanosecond spectroscopy in a heterogeneous donor- bridge-acceptor (D-B-A) system, where D = ruthenium terpyridine complex, B = p-oligo(phenylene) and A = TiO2. The forward ET rate (from 0.85 to 3.7 ps-1) is faster than the nonequilibrium vibrations relaxation rate of the hot 3MLCT (metal-to-ligand charge transfer) state of the donor (12 ps-1 in solution). The back ET occurs on the microsecond time scale. Regarding the distance dependence behaviour, damping factors 0.16 and 0.47 Å-1 of the forward and the back ET respectively are obtained. These results confirm that the damping factor is not only linked to the nature of the molecular bridge but to the full D-B-A system. This unusual low damping factor observed for the forward ET is attributed to a decrease of the tunnelling energy gap ΔE, which is induced by the nonequilibrium vibrations at the donor-bridge interface. This enhanced electron transmission is briefly discussed within the concept of a nonequilibrium polaron relaxation towards the dissipative acceptor. In this case, the dissipation of the excess vibrational energy and the electron transfer occur in a synchronized cooperative way.

The influence of monovalent cation halide additives on the optical, excitonic, and electrical properties of CH$_{3}$NH$_{3}$PbI$_{3}$ perovskite is reported. Monovalent cation halide with similar ionic radii to Pb$^{2+}$, including Cu$^{+}$, Na$^{+}$, and Ag$^{+}$, have been added to explore the possibility of doping. Significant reduction of sub-bandgap optical absorption and lower energetic disorder along with a shift in the Fermi level of the perovskite in the presence of these cations has been observed. The bulk hole mobility of the additive-based perovskites as estimated using the space charge limited current method exhibits an increase of up to an order of magnitude compared to the pristine perovskites with a significant decrease in the activation energy. Consequentially, enhancement in the photovoltaic parameters of additive-based solar cells is achieved. An increase in open circuit voltage for AgI (≈1.02 vs 0.95 V for the pristine) and photocurrent density for NaI- and CuBr-based solar cells (≈23 vs 21 mA cm$^{−2}$ for the pristine) has been observed. This enhanced photovoltaic performance can be attributed to the formation of uniform and continuous perovskite film, better conversion, and loading of perovskite, as well as the enhancement in the bulk charge transport along with a minimization of disorder, pointing towards possible surface passivation.

After rapid progress over the past five years, organic–inorganic perovskite solar cells (PSCs) currently exhibit photoconversion efficiencies comparable to the best commercially available photovoltaic technologies. However, instabilities in the materials and devices, primarily due to reactions with water, have kept PSCs from entering the marketplace. Here, laser beam induced current imaging is used to investigate the spatial and temporal evolution of the quantum efficiency of perovskite solar cells under controlled humidity conditions. Several interesting mechanistic aspects are revealed as the degradation proceeds along a four-stage process. Three of the four stages can be reversed, while the fourth stage leads to irreversible decomposition of the photoactive perovskite material. A series of reactions in the PbI2-CH3NH3I-H2O system explains the interplay between the interactions with water and the overall stability. Understanding of the degradation mechanisms of PSCs on a microscopic level gives insight into improving the long-term stability.

Energy band alignments at heterointerfaces play a crucial role in defining the functionality of semiconductor devices, yet the search for material combinations with suitable band alignments remains a challenge for numerous applications. In this work, we demonstrate how changes in deposition conditions can dramatically influence the functional properties of an interface, even within the same material system. The energy band alignment at the heterointerface between Cu2O and ZnO was studied using photoelectron spectroscopy with stepwise deposition of ZnO onto Cu2O and vice versa. A large variation of energy band alignment depending on the deposition conditions of the substrate and the film is observed, with valence band offsets in the range Delta E-VB = 1.45-2.7 eV. The variation of band alignment is accompanied by the occurrence or absence of band bending in either material. It can therefore be ascribed to a pinning of the Fermi level in ZnO and Cu2O, which can be traced back to oxygen vacancies in ZnO and to metallic precipitates in Cu2O. The intrinsic valence band offset for the interface, which is not modified by Fermi level pinning, is derived as Delta E-VB approximate to 1.5 eV, being favorable for solar cell applications.

1,6-Dithiophenol-substituted perylene organic sensitizer 1 was synthesized, and its photovoltaic properties in dye-sensitized solar cells were assessed. When anchored onto TiO2 film, the dye exhibits an unprecedented incident monochromatic photon-to-current conversion efficiency of 87 % and yields a power conversion efficiency of 6.8 % under standard AM 1.5 solar conditions.

We performed ab initio simulations aimed at identifying the atomistic and electronic structure origin of the high valence and conduction band, and band gap tunability of halide perovskites. We found that the two key ingredients are the overlap between bivalent cation and halide atomic orbitals, and the electronic charge of the bottom of the conduction band (CBM) state on the Sn or Pb atoms. In particular, we found that lower gaps are associated to higher negative antibonding overlap, and higher CBM charge on the bivalent cation. Both overlap and CBM charge on Sn/Pb can be tuned by the chemical nature of halide, bi and monovalent cation, as well as the symmetry of crystal structure. On the basis of our results we provide some practical rules to tune the valence band maximum, conduction band minimum, and band gap in this class of materials., Comment: 13 pages, 9 figures - contains SI

The abundant pigment-protein membrane complex photosystem-I (PS-I) is at the heart of the Earth’s energy cycle. It is the central molecule in the “Z-scheme” of photosynthesis, converting sunlight into the chemical energy of life. Commandeering this intricately organized photosynthetic nanocircuitry and re-wiring it to produce electricity carries the promise of inexpensive and environmentally friendly solar power. We here report that dry PS-I stabilized by surfactant peptides functioned as both the light-harvester and charge separator in solar cells self-assembled on nanostructured semiconductors. Contrary to previous attempts at biophotovoltaics requiring elaborate surface chemistries, thin film deposition, and illumination concentrated into narrow wavelength ranges the devices described here are straightforward and inexpensive to fabricate and perform well under standard sunlight yielding open circuit photovoltage of 0.5 V, fill factor of 71%, electrical power density of 81 µW/cm[superscript 2] and photocurrent density of 362 µA/cm[superscript 2], over four orders of magnitude higher than any photosystem-based biophotovoltaic to date., Intel Corporation, Knut and Alice Wallenberg Foundation (Fellowship), John Simon Guggenheim Memorial Foundation (Guggenheim Fellowship), National Science Foundation (U.S.). Nanoscale Interdisciplinary Research Team

Conventional dye-sensitized solar cells have excellent charge collection efficiencies, high open-circuit voltages and good fill factors. However, dye-sensitized solar cells do not completely absorb all of the photons from the visible and near-infrared domain and consequently have lower short-circuit photocurrent densities than inorganic photovoltaic devices. Here, we present a new design where high-energy photons are absorbed by highly photoluminescent chromophores unattached to the titania and undergo Forster resonant energy transfer to the sensitizing dye. This novel architecture allows for broader spectral absorption, an increase in dye loading, and relaxes the design requirements for the sensitizing dye. We demonstrate a 26% increase in power conversion efficiency when using an energy relay dye (PTCDI) with an organic sensitizing dye (TT1). We estimate the average excitation transfer efficiency in this system to be at least 47%. This system offers a viable pathway to develop more efficient dye-sensitized solar cells.

Its lower bandgap makes formamidinium lead iodide (FAPbI(3)) a more suitable candidate for single-junction solar cells than pure methylammonium lead iodide (MAPbI(3)). However, its structural and thermodynamic stability is improved by introducing a significant amount of MA and bromide, both of which increase the bandgap and amplify trade-off between the photocurrent and photovoltage. Here, we simultaneously stabilized FAPbI(3 )into a cubic lattice and minimized the formation of photoinactive phases such as hexagonal FAPbI(3) and PbI2 by introducing 5% MAPbBr(3) , as revealed by synchrotron X-ray scattering. We were able to stabilize the composition (FA(0.95)MA(0.05)Cs(0.05))Pb(I-0.95 Br-0.05)(3), which exhibits a minimal trade-off between the photocurrent and photovoltage. This material shows low energetic disorder and improved charge-carrier dynamics as revealed by photothermal deflection spectroscopy (PDS) and transient absorption spectroscopy (TAS), respectively. This allowed the fabrication of operationally stable perovskite solar cells yielding reproducible efficiencies approaching 22%.

In the ongoing intense quest to increase the performance of perovskite solar cells, optimizing the morphology of perovskite material has become imperative to achieve high power conversion efficiencies. Despite the fact that nucleation plays a key role in controlling the crystal morphology, very little is known about the nucleation and crystal growth processes. Here, we perform metadynamics simulations of nucleation of methylammonium lead triiodide (MAPI) in order to unravel the atomistic details of perovskite crystallization from a γ-butyrolactone solution. The metadynamics trajectories show that the nucleation process takes place in several stages. Initially, dense amorphous clusters mainly consisting of lead and iodide appear from the homogeneous solution. These clusters evolve into lead iodide (PbI2)-like structures. Subsequently, methylammonium (MA+) ions diffuse into these PbI2-like aggregates triggering the transformation into a perovskite crystal through a solid–solid transformation. These enticing results allowed us to design new experimental strategies to rationally control the dimensions of MAPI grains using the spin-coating technique and to engineer homogeneous nucleation and growth of MAPI single crystals. The experimental results amply support our unprecedented observations related to the critical role of monovalent cations in inducing the nucleation process in lead halide perovskites.

The present invention relates to novel compounds that are useful as ligands in organometallic dyes. More particularly, the invention relates to dyes comprising the compounds, said dyes being sensitizing dyes useful in solar cell technology. According to an embodiment, the present invention discloses new ruthenium dyes and their application in dye-sensitized solar cells (DSC).The referrerd ruthenium dyes with new structural features can be easily synthesized, show more than 85% light-to-electricity conversion efficiency and a higher than 9% cell efficiency.

Due to its abundance, scalability, and nontoxicity, Cu2O has attracted extensive attention toward solar energy conversion, and it is the best performing metal oxide material. Until now, the high efficiency devices are all planar in structure, and their photocurrent densities still fall well below the theoretical value of 14.5 mA cm(-2) due to the incompatible light absorption and charge carrier diffusion lengths. Nanowire structures have been considered as a rational and promising approach to solve this issue, but due to various challenges, performance improvements through the use of nanowires have rarely been achieved. In this work, we develop a new synthetic method to grow Cu2O nanowire arrays on conductive fluorine-doped tin oxide substrates with well-controlled phase and excellent electronic and photonic properties. Also, we introduce an innovative blocking layer strategy to enable high performance. Further, through material engineering by combining a conformal nanoscale p-n junction, durable protective overlayer, and uniform catalyst decoration, we have successfully fabricated Cu2O nanowire array photocathodes for hydrogen generation from solar water splitting delivering unprecedentedly high photocurrent densities of 10 mA cm(-2) and stable operation beyond 50 h, establishing a new benchmark for metal oxide based photoelectrodes.

A series of novel near-infrared-absorbing zinc phthalocyanines bearing donor-chromophore-acceptor/anchoring groups have been synthesized to investigate their influence on solar cell performance. With the aim of extending the absorption spectra while maintaining the minimization of aggregation by using 2,6-diphenylphenoxy bulky groups, the benzodithiadazole was used as an electron acceptor moiety and the carboxylic acid and the anhydride unit were adopted as an anchoring group. These dyes have been used as sensitizers in dye-sensitized solar cells, and their performance has been compared with that of phthalocyanine (Pc) sensitizer TT40, which has an ethynyl bridge between the anchoring carboxy group and the macrocycle. The new ZnPcs show an extended pi-conjugated system which produces red maximum of ca. 10 nm in comparison to that of TT40. Despite the red-shifted spectral response, these cells gave modest power conversion efficiencies of ca. 3% because of the lower lowest unoccupied molecular orbital level of the Pcs, which limits the electron injection from the dyes to the TiO2.

A dye sensitized solar cell, wherein a compacting compound whose molecular structure comprises a terminal group, a hydrophobic part and an anchoring group is co-adsorbed together with the dye on the semi-conductive metal oxide layer of the photoanode, forming a dense mixed self-assembled monolayer.

In a high capacity primary or secondary cell, the active material of at least one of the electrodes is selected from transition metal oxides or their (partially) lithiated forms, such as TiO2, Nb2O5, HfO2, MnO2, LiyNiO2, LiyCo2, Ldy(NiCo)O2, or LiyMn2O4, in the form of electrically interconnected nanocrystalline particles of 1-250 nm. size. Pref. the particles are mixed with graphite and a binder, e.g. ethylene-propylene-diene monomer or PTFE, and compressed to form the electrode.

The organic small molecule 4,4',4",4"'-(5,5-dimethoxycyclopenta-1,3-diene-1,2,3,4-tetrayl)tetrakis(N,N-bis(4-methoxyhenyl)aniline (CPDA 1), shows electrochemical properties very close to spiro-OMeTAD indicating a high compatibility with PSC systems for its use as a hole transport material (HTM). The implementation of the cyclopentadiene dimethyl acetale core helps to red shift the absorption onset of the films as well as provide a flexible spatial configuration of the molecule, which is essential for optimum film forming properties. Transient and steady state emission analysis as well as hole mobility measurements indicate that the new HTM allows a better charge extraction, transport and separation than the spiro-OMeTAD reference compound. PSCs based on the new CPDA 1 show a PCE close to 23% with lower hysteresis than its analogue. Stability studies performed under ambient, heated and humid conditions all showed that CPDA 1 is over-performing spiro-OMeTAD. Furthermore the production cost of CPDA 1 is about 10 times lower than that of spiro-OMeTAD, contributing to render PSCs more affordable.

A series of donor-chromophore-anchor (D-C-A) sensitizers comprising the diketopyrrolopyrrole (DPP) chromophore were synthesized and tested in both I-3(-)/I- and Co[(bpy)](3+/2+) redox shuttle DSC devices. The dye series was strategically designed to elucidate structure-property relationships, concerning overall performance and compatibility with these two electrolytes. Selective fluorine incorporation improved I-3(-)/I--based DSC performance, while hindering performance with the positively charged cobalt-based redox shuttle. Incorporation of a pyridine heterocycle into the DPP chromophore increased spectral breadth, but decreased performance metrics for both electrolyte systems. These results are understood through detailed electrochemical, photophysical, and computational studies.

We report on the site-selective synthesis of PCBM-like [70]fullerene site-isomers, where the elusive -site-isomers are, for the first time, the major product in a (cyclo)addition chemical reaction involving [70]fullerene. The reaction involves an straightforward cyclopropanation of [70]fullerene from sulfonium salts, affording a mixture of and site-isomers in good yields. Amazingly, the preference for the - or -site-isomer can be efficiently controlled by means of the solvent polarity! DFT theoretical calculations (DMF and toluene) nicely predict that, although the formation of the -adduct is, as expected, thermodynamically favored, the selectivity of the process is determined by the energy difference of the respective transition states. Furthermore, the employ of or/and site-isomers, as pure materials or as a mixture of them, used as templating agent, has been evaluated in perovskite solar cells. The positive influence of the [70]fullerenes by passivating the voids/pin-holes and/or deep slits, is reflected in highly efficient and stable bulk heterojunction perovskite solar cells, whose performance (around 20%) is slightly but consistently depending on the isomeric fullerene composition. These experimental findings pave the way to investigate a new reactivity on C-70 and to explore the properties of the less-known -derivatives.

Perovskite solar cells are one of the most promising photovoltaic technologies, although their molecular level design and stability toward environmental factors remain a challenge. Layered 2D Ruddlesden-Popper perovskite phases feature an organic spacer bilayer that enhances their environmental stability. Here, the concept of supramolecular engineering of 2D perovskite materials is demonstrated in the case of formamidinium (FA) containing A(2)FA(n-1)Pb(n)I(3n+1) formulations by employing (adamantan-1-yl)methanammonium (A) spacers exhibiting propensity for strong Van der Waals interactions complemented by structural adaptability. The molecular design translates into desirable structural features and phases with different compositions and dimensionalities, identified uniquely at the atomic level by solid-state NMR spectroscopy. For A(2)FA(2)Pb(3)I(10), efficiencies exceeding 7% in mesoscopic device architectures without any additional treatment or use of antisolvents for ambient temperature film deposition are achieved. This performance improvement over the state-of-the-art FA-based 2D perovskites is accompanied by high operational stability under humid ambient conditions, which illustrates the utility of the approach in perovskite solar cells and sets the basis for advanced supramolecular design in the future.

A photovoltaic cell comprising an electrolyte which comprises a hole conductor compound as redox system.

A Ca2+ sensor based on the admittance change of synthetic membranes supported on derivatized silicon electrodes is reported. The ion-sensitive membranes consist of mixed monolayers of phospholipid and the Ca2+-ligand ETH 1001. The electrodes are characterized electrochem. and their sensor performances are described. Through ion complexation by the neutral ligand, elec. charges are incorporated in the low-dielec.-const. environment of the sensitive layer. The no. of charged complexes and thus the membrane admittance depend on the ion content of the electrolyte. The membrane response to Ca2+ and the competitive binding of other cations are studied. A noncompetitive process is obsd. if several ionophores, each one specific for a different ion, are incorporated in the membrane. Mixed layers with tetradecyl-18-crown-6 and ETH 1001 show both K+ and Ca2+ sensitivity. These electrodes allow direct comparison with a previously reported K+ sensor based on tetradecyl-18-crown-6. [on SciFinder (R)]

Photoelectrochemical (PEC) cells offer the ability to convert electromagnetic energy from our largest renewable source, the Sun, to stored chemical energy through the splitting of water into molecular oxygen and hydrogen. Hematite (alpha-Fe2O3) has emerged as a promising photo-electrode material due to its significant light absorption, chemical stability in aqueous environments, and ample abundance. However, its performance as a water-oxidizing photoanode has been crucially limited by poor optoelectronic properties that lead to both low light harvesting efficiencies and a large requisite overpotential for photoassisted water oxidation. Recently, the application of nanostructuring techniques and advanced interfacial engineering has afforded landmark improvements in the performance of hematite photoanodes. In this review, new insights into the basic material properties, the attractive aspects, and the challenges in using hematite for photoelectrochemical (PEC) water splitting are first examined. Next, recent progress enhancing the photocurrent by precise morphology control and reducing the overpotential with surface treatments are critically detailed and compared. The latest efforts using advanced characterization techniques, particularly electrochemical impedance spectroscopy, are finally presented. These methods help to define the obstacles that remain to be surmounted in order to fully exploit the potential of this promising material for solar energy conversion.

The present invention relates to a compound of formula (I) based on compound derived from Acceptor-Donor-Acceptor (A-D-A) oligothiophenes based on heteroacene core and used as hole transporting material in a photovoltaic device, in particular in a solid state solar cell.

We re-assess experimental soft X-ray absorption spectra of the oxygen K-shell which we recorded operando from iron oxide during photoelectrochemical water splitting in KOH electrolyte. In particular, we refer to recently reported transitional electron hole states which originate within the charge carrier depletion layer of the iron oxide and on the iron oxide surface. For the latter we find that an intermediate oxy-peroxo species is formed on the iron oxide with increasing bias potential, which disappears upon further polarization of the electrode, concomitantly with the evolution and disappearance of the aforementioned surface state. The oxygen spectra contain also the spectroscopic signatures of the electrolyte water, the position of which changes with increasing bias potential towards lower X-ray energies, revealing the breaking and formation of hydrogen bonds in the water during the experiment. Combined with potential dependent impedance spectroscopy data we are able to sketch the molecular structure of chemical intermediates and their charge carrier dynamics. (C) 2015 Elsevier B.V. All rights reserved.

The formation of H-aggregates as a function of solution, substrate and ambient variables is considered for the merocyanine dye 3-acetyl-5-12-(3-ethyl-2-benzothiazolydene) rhodanine. Colloidal semiconductor particles are shown to be a powerful tool to control the size of the aggregates. In water the blue shifted absorption band has been assigned to a dimer. Its spectrum has been isolated and the thermodynamical variables derived for the dissociation reaction are: ΔrG0=21.16 kJ/mol, ΔrH0=32.36 kJ/mol and ΔrS0=37.24 J/mol K. Exciton band absorption maxima for aggregates in solution and at the water-TiO2 and water-Al2O3 interface, respectively, have been correlated to the aggregation geometry using the extended dipole model in conjunction with crystallographic data. Microcrystals showing a hypsochromical shift in the absorption band have been produced within the pores of nanocrystalline semiconductor films. The calculation shows that these aggregates are needle shaped and are composed of about 2250 monomer units. A broad emission band appears when the organic molecules assemble in a head to tail stacking geometry which could be attributed to excimer fluorescence. It is not quenched by charge injection into TiO2 and indicates the existence of dislocations within the merocyanine stacks.