Hybrid organic–inorganic perovskites have been established as good candidate materials for emerging photovoltaics, with device efficiencies of over 22% being reported. There are currently only two organic cations, methylammonium and formamidinium, which produce 3D perovskites with band gaps suitable for photovoltaic devices. Numerous computational studies have identified azetidinium as a potential third cation for synthesizing organic–inorganic perovskites, but to date no experimental reports of azetidinium containing perovskites have been published. Here we prepare azetidinium lead iodide for the first time. Azetidinium lead iodide is a stable, bright orange material which does not appear to form a 3D or a 2D perovskite. It was successfully used as the absorber layer in solar cells. We also show that it is possible to make mixed cation devices by adding the azetidinium cation to methylammonium lead iodide. Computational studies show that the substitution of up to 5% azetidinium into the methylammonium lead iodide is energetically favourable and that phase separation does not occur at these concentrations. Mixed azetidinium–methylammonium cells show improved performance and reduced hysteresis compared to methylammonium lead iodide cells.

Perovskite solar cells have gained increasing interest, especially after reaching performances which are comparable with mature silicon PV technologies. However, the perovskite crystalline structure CH3NH3PbI3 is unstable in the presence of moisture, which leads to fast degradation under ambient conditions. The commercialisation of perovskite solar cells will only be achieved with the engineering of long term stable materials. We report a modified perovskite absorber layer obtained by adding methylammonium iodide (MAI) and tetrabutylammonium (TBA) iodide. The incorporation of TBA improves the film coverage, reducing the number of pinholes. X-ray diffraction analysis suggests that, in common with other mixed larger cation perovskites, two distinct phases coexist: a 3D perovskite material and a 2D layered material. The TBA containing perovskite films showed improved hydrophobicity, which contributed to significantly higher moisture stability. The cells maintained their original PCE after 45 days under ambient conditions without encapsulation. In comparison, the CH3NH3PbX3 3D perovskite device lost more than 60% of its original efficiency over the same time.

Perovskite solar cells (PSC) are shown to behave as coupled ionic–electronic conductors with strong evidence that the ionic environment moderates both the rate of electron–hole recombination and the band offsets in planar PSC. Numerous models have been presented to explain the behaviour of perovskite solar cells, but to date no single model has emerged that can explain both the frequency and time dependent response of the devices. Here we present a straightforward coupled ionic–electronic model that can be used to explain the large amplitude transient behaviour and the impedance response of PSC.

•A new copper complex bearing thienyl-bipyridine ligands was prepared.•Dye-sensitized solar cells using this complex were constructed and evaluated.•Comparisons are made with an analogous dye which lacks the thiophene motifs.The 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.Figure optionsDownload full-size imageDownload as PowerPoint slide

We present a method for the polymerization of low molecular weight hydrogelators to form polymers with unique structures. Carbazole-protected amino acids are shown to form hydrogels by self-assembly into fibrous structures. We show that is possible to directly electropolymerize the hydrogels. This results in the formation of microporous electrochromic polymers with distinctive structure. Polymers formed from the same gelator without the pregelation step show more compact structures. This method opens the possibility of creating polymers templated from pre-assembled gels that have the potential to be used in a wide range of applications.

•Simple technique for the preparation of MAPbI3 investigated.•A glove box and an inert atmosphere were not necessary.•Only a spin coater, hotplate, desiccator and low vacuum pump required.•Glassy films were produced giving 12.7% efficiency for a planar device.Vacuum-vapor assisted solution processing has been investigated as a simple and low cost method for preparing perovskite solar cells without a glove box. The devices were prepared in ambient air without using a high vacuum or an inert atmosphere. A maximum efficiency of 12.7% for planar perovskite (CH3NH3PbI3) devices was obtained. The perovskite films could be stored in air (20 °C, ∼50% humidity) for up to 14 days without discoloration or the appearance of crystalline lead iodide in the films.

Thin film lead halide perovskite cells, where the perovskite layer is deposited directly onto a flat titania blocking layer, have reached AM 1.5 efficiencies of over 15%,1 showing that the mesoporous scaffold used in early types of perovskite solar cells is not essential. We used a variety of techniques to gain a better understanding of thin film perovskite cells prepared by a solution-based method. Twelve cells were studied, which showed AM 1.5 efficiencies of ∼11%. The properties of the cells were investigated using impedance spectroscopy, intensity-modulated photovoltage spectroscopy (IMVS), intensity-modulated photocurrent spectroscopy (IMPS), and open-circuit photovoltage decay (OCVD). Despite the fact that all 12 cells were prepared at the same time under nominally identical conditions, their behavior fell into two distinct groups. One half of the cells exhibited ideality factors of m ≈ 2.5, and the other half showed ideality factors of m ≈ 5. Impedance spectroscopy carried out under illumination at open circuit for a range of intensities showed that the cell capacitance was dominated by the geometric capacitance of the perovskite layer rather than the chemical or diffusion capacitance due to photogenerated carriers. The voltage dependence of the recombination resistance gave ideality factors similar to those derived from the intensity dependence of the open-circuit voltage. The IMVS time constant was determined by the product of the geometric capacitance and the recombination resistance. The two types of cells gave very different OCVD responses. The cells with m ≈ 2.5 showed a persistent photovoltage effect that was absent in the case of the cells with higher ideality factors. The IMPS responses provide evidence of minor efficiency losses by recombination under short-circuit conditions.

The reduction of the redox mediator ferricyanide, [Fe(CN)6]3−, by a range of algal and bacterial species, is frequently measured to probe plasma membrane ferrireductase activity or to quantify the reducing power of algal/bacterial biofilms and suspensions. In this study we have used rotating disk electrochemistry (RDE) to investigate the reduction of ferricyanide by the model organism Chlorella vulgaris. Importantly, we have seen that the diffusion limited current due to the oxidation of ferrocyanide, [Fe(CN)6]4−, at the electrode decreased linearly as C. vulgaris was added to the solution, even though in a pure ferrocyanide solution the algae are not able to reduce the mediator further and are simply spectator ‘particles’. We attribute this effect to trapping of ferrocyanide at the cell surface, with up to 14% of the ferrocyanide missing from the solution at the highest cell concentration. The result has important implications for all techniques that use electrochemistry and other concentration dependent assays (e.g. fluorescence and colourimetry) to monitor ferrocyanide concentrations in the presence of both biofilms and cell suspensions. Analyte trapping could lead to a substantial underestimation of the concentration of reduced product.

We report the surface nucleated growth of self-assembled dipeptide films. The seeding-layer was a thin dipeptide film with a globular structure. Placing the seeding-layer in contact with dipeptide led to growth of fibres overnight. Active enzymes were incorporated into the gel by adding them to the growth solution.

The synthesis, properties and application of a Cu(2,2′-biquinoline-4,4′-dicarboxylic acid)2 complex in dye-sensitized solar cells (DSSC) are described. The complex is electrochemically stable and strongly absorbing with a molar extinction coefficient at λ(max) = 564 nm of 11700 M−1 cm−1 (in MeOH). Experimental and computational data indicate that the HOMO, LUMO and electronic excited state energy levels are appropriate for functionality in a DSSC. From cyclic voltammetry the HOMO is estimated to be −5.27 eV, as supported by computational work, which locates the HOMO at −5.78 eV. From electrochemical, absorption and emission experiments, the MLCT energy levels are expected to be appropriate for electron injection into the TiO2 conduction band. Our computations support this and locate the key MLCT transition at 563 nm. Despite this, the efficiency in DSSCs is extremely low (<0.1%) suggesting that the dye does not inject excited electrons into the TiO2 conduction band.

The pH drop associated with sugar recognition and binding by boronic acids has been used to initiate the formation of gels from dipeptide gelators. Gels formed in the presence of fructose, but not glucose which has a weaker binding constant to boronic acids.

There is currently renewed interest in aqueous dye-sensitized solar cells (DSCs). Water ingress in conventional DSCs leads to a loss of efficiency; one solution to this problem is to optimize the cells to work in the presence of water. The aim is to create a stable cell and to avoid the need for buffer layers and encapsulation that increase device cost. Water containing electrolytes generally give lower photocurrents than those based on organic solvents, a problem that has in part been attributed to poor pore filling by the aqueous electrolyte. Here, two sets of cells have been made that are identical except for the nature of the solvent (water or acetonitrile). Photocurrent mapping has been used to compare spatially resolved inhomogeneities in the current density. High-resolution transmission mapping (3906 data points/cm2) has been used to decouple dye coverage and film thickness from electrolyte permeation. Filling cells using heating and vacuum was found to improve water electrolyte permeation. Photocurrent maps suggest that dye desorption occurs adjacent to the filling holes in both acetonitrile- and water-based cells, with significantly more dye desorbed in the water-based cells. The loss of dye was attributed to desorption by the tert-butyl pyridine base in the electrolyte.

This study focuses on porous ceramics as a promising new type of anode material for photo-microbial fuel cells (p-MFCs). The anodes were made from titanium dioxide and chemical vapour deposition was used to coat them with a layer of fluorine doped tin oxide (FTO) to make them conducting. Chlorella vulgaris biofilms were grown in the millimetre sized pores of the ceramic electrodes, producing an extensive extra cellular matrix that was anchored directly to the electrode surface. In contrast algal cells grown on carbon felt appeared misshapen and lacked a continuous extra cellular matrix. A preliminary comparison of different anodes in p-MFCs showed that the power density was ∼16 times higher on a ceramic anode compared to the best performing carbon anode. Good power densities were also found for algae grown directly onto FTO coated glass, but in contrast to the ceramic anodes the biofilm did not adhere strongly to the planar surface and was easily removed or damaged.

Over the last 12 months a number of papers have been published which shed light on the processes that control the self-assembly of peptides into fibrous hydrogel networks. A number of new properties of dipeptide hydrogels have also been reported. This article highlights recent activity in the area of peptide self-assembly, with a particular focus on tri-peptides, di-peptides and protected amino acids.

Optical waveguide spectroscopy has been used to study the real-time adsorption of ruthenium 535-bisTBA (N-719) dye in mesoporous nanocrystalline titanium dioxide films of the type used in dye-sensitized solar cells (DSCs). Porous titania films were prepared on top of gold substrates, and prism coupling was used to create a guided wave in the nanocrystalline film. The conditions under which a guided mode can be excited are dependent on both the refractive index and the extinction coefficient of the mesoporous layer, where the mesoporous layer refers to both the nanocrystals of TiO2 and the composition of the pores. It was therefore possible to track changes in dye concentration in the pores in real time. The total concentration of dye in the film appeared to continue increasing even after 22 h, in contrast to the amount of dye in the pores that was able to absorb light at 632.8 nm, which saturated after ∼5 h. The total concentration of dye molecules was 2.47 × 10−4 mol cm−3 as a function of the total pore volume at equilibrium; assuming a regular array of spherical particles with a porosity of 0.5, this translates to 10−6 moles m−2. The value of surface coverage obtained from OWS is similar to that calculated by dye desorption studies and is close to the value previously reported for the N3 dye. (Nazeeruddin, M. K.; Pechy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Gratzel, M. J. Am. Chem. Soc. 2001, 123, 1613). A preliminary model that simulates the increase in dye as measured by optical modes has also been developed and shows that the data does not fit a single diffusion coefficient.

The dipeptide amphiphile Fmoc-Leu-Gly-OH has been induced to self-assemble into thin surface-supported hydrogel gel films and gap-spanning hydrogel membranes. The thickness can be closely controlled, giving films/membranes from tens of nanometers to millimeters thick. SEM and TEM have confirmed that the dipeptides self-assemble to form fibers, with the membranes resembling a dense “mat” of entangled fibers. The films and membranes were stable once formed. The films could be reversibly dried and collapsed, then reswollen to regain the gel structure.

Cd0.1Zn0.9Se quantum dots with fluorescent emission centered on 614 nm were covalently coupled to a 11-amino-1-undecanethiol monolayer self-assembled on a gold surface. A 594 nm laser was used to excite surface plasmons in the gold film and the resulting surface plasmon enhanced fluorescence of the quantum dots was measured with a photomultiplier. The application of negative potentials (versus Ag/AgCl) led to a decrease in the surface plasmon enhanced fluorescence signal, the fluorescence signal recovered if the cell potential was returned to 0 V or open circuit. These results show that the fluorescence emission of attached quantum dots can be tuned by the application of an electrical potential in an aqueous environment, which may be relevant to quantum dot applications in biosensing.

The increasing interest in using nanoporous and mesoporous films for a range of applications including sensors and solar cells has created a concomitant demand for the development of analytical methodologies to study the films in situ. Especially important is the ability to quantify the filling of such films with guest molecules, be they dyes or proteins. In this paper we have demonstrated a simple methodology for the highly sensitive monitoring of nanoporous titania films as protein is both adsorbed in, and removed from the film matrix: optical waveguide mode spectroscopy. Porous titania films of thickness between 0.5 and 1.5 μm were created on gold slides by the deposition of a colloidal suspension of titanium dioxide nanoparticles with a phytate binder. Absorption of cytochrome c into the highly porous titanium structure was followed by both optical waveguide spectroscopy (OWS) and electrochemistry. OWS showed that saturation occurred when 27% of the pore volume was filled with cytochrome c and initial diffusion coefficients of 10−17 m2 s−1 were measured for cytochrome c within the pores. Electrochemical measurements displayed good agreement with OWS measurements and showed that the protein permeated all the way through the porous film to the gold substrate. The results further demonstrate that the OWS method is more than two orders of magnitude more sensitive than classical electrochemical methods conventionally used to study such systems, and is not dependent on having a redox-active adsorbate.

The reduction of the redox mediator ferricyanide, [Fe(CN)6]3−, by a range of algal and bacterial species, is frequently measured to probe plasma membrane ferrireductase activity or to quantify the reducing power of algal/bacterial biofilms and suspensions. In this study we have used rotating disk electrochemistry (RDE) to investigate the reduction of ferricyanide by the model organism Chlorella vulgaris. Importantly, we have seen that the diffusion limited current due to the oxidation of ferrocyanide, [Fe(CN)6]4−, at the electrode decreased linearly as C. vulgaris was added to the solution, even though in a pure ferrocyanide solution the algae are not able to reduce the mediator further and are simply spectator ‘particles’. We attribute this effect to trapping of ferrocyanide at the cell surface, with up to 14% of the ferrocyanide missing from the solution at the highest cell concentration. The result has important implications for all techniques that use electrochemistry and other concentration dependent assays (e.g. fluorescence and colourimetry) to monitor ferrocyanide concentrations in the presence of both biofilms and cell suspensions. Analyte trapping could lead to a substantial underestimation of the concentration of reduced product.

The increasing interest in using nanoporous and mesoporous films for a range of applications including sensors and solar cells has created a concomitant demand for the development of analytical methodologies to study the films in situ. Especially important is the ability to quantify the filling of such films with guest molecules, be they dyes or proteins. In this paper we have demonstrated a simple methodology for the highly sensitive monitoring of nanoporous titania films as protein is both adsorbed in, and removed from the film matrix: optical waveguide mode spectroscopy. Porous titania films of thickness between 0.5 and 1.5 μm were created on gold slides by the deposition of a colloidal suspension of titanium dioxide nanoparticles with a phytate binder. Absorption of cytochrome c into the highly porous titanium structure was followed by both optical waveguide spectroscopy (OWS) and electrochemistry. OWS showed that saturation occurred when 27% of the pore volume was filled with cytochrome c and initial diffusion coefficients of 10−17 m2 s−1 were measured for cytochrome c within the pores. Electrochemical measurements displayed good agreement with OWS measurements and showed that the protein permeated all the way through the porous film to the gold substrate. The results further demonstrate that the OWS method is more than two orders of magnitude more sensitive than classical electrochemical methods conventionally used to study such systems, and is not dependent on having a redox-active adsorbate.

Perovskite solar cells (PSC) are shown to behave as coupled ionic–electronic conductors with strong evidence that the ionic environment moderates both the rate of electron–hole recombination and the band offsets in planar PSC. Numerous models have been presented to explain the behaviour of perovskite solar cells, but to date no single model has emerged that can explain both the frequency and time dependent response of the devices. Here we present a straightforward coupled ionic–electronic model that can be used to explain the large amplitude transient behaviour and the impedance response of PSC.

We present a method for the polymerization of low molecular weight hydrogelators to form polymers with unique structures. Carbazole-protected amino acids are shown to form hydrogels by self-assembly into fibrous structures. We show that is possible to directly electropolymerize the hydrogels. This results in the formation of microporous electrochromic polymers with distinctive structure. Polymers formed from the same gelator without the pregelation step show more compact structures. This method opens the possibility of creating polymers templated from pre-assembled gels that have the potential to be used in a wide range of applications.

We report the surface nucleated growth of self-assembled dipeptide films. The seeding-layer was a thin dipeptide film with a globular structure. Placing the seeding-layer in contact with dipeptide led to growth of fibres overnight. Active enzymes were incorporated into the gel by adding them to the growth solution.

Over the last 12 months a number of papers have been published which shed light on the processes that control the self-assembly of peptides into fibrous hydrogel networks. A number of new properties of dipeptide hydrogels have also been reported. This article highlights recent activity in the area of peptide self-assembly, with a particular focus on tri-peptides, di-peptides and protected amino acids.

This study focuses on porous ceramics as a promising new type of anode material for photo-microbial fuel cells (p-MFCs). The anodes were made from titanium dioxide and chemical vapour deposition was used to coat them with a layer of fluorine doped tin oxide (FTO) to make them conducting. Chlorella vulgaris biofilms were grown in the millimetre sized pores of the ceramic electrodes, producing an extensive extra cellular matrix that was anchored directly to the electrode surface. In contrast algal cells grown on carbon felt appeared misshapen and lacked a continuous extra cellular matrix. A preliminary comparison of different anodes in p-MFCs showed that the power density was ∼16 times higher on a ceramic anode compared to the best performing carbon anode. Good power densities were also found for algae grown directly onto FTO coated glass, but in contrast to the ceramic anodes the biofilm did not adhere strongly to the planar surface and was easily removed or damaged.