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We report on the use of a fluorinated imidazolium ionic liquid as a source of iodide ions in solvent-based electrolytes for DSSCs. Efficient dye regeneration and fast charge transport in the fluorinated electrolyte result in an overall improvement of the device performances compared to conventional hydrogenated ionic liquids. © 2012 Elsevier B.V. All rights reserved.

Two new macrocyclic structures containing 8-hidroxyisoalloxazine and 1,5-dihydroxyanthracene moieties linked by aliphatic chains of different lengths ( n = 4 and 6) were designed and synthesized in order to study photoinduced electron transfer (PET) processes from the anthracene unit towards the isoalloxazine singlet excited state induced by structural changes due to different intrachromophoric distances and orientations. The compounds have been fully characterized by NMR spectroscopy and the X-ray solid state structures of both macrocycles have been elucidated. Photophysical measurements, including continuous wavelength photoinduced absorption (cw-PIA), at room temperature and 77 K have been carried out in order to investigate the influence of the close contacts between the aromatic groups (π–π stacking) on the photophysical properties of the macrocycles.

Two new metal-free organic dyes, CR29 and CR52, with high extinction coefficients in the visible spectral region between 400–650 nm, have been synthesized. The donor–acceptor structure of the dyes feature benzodithiophene moieties BDT1 and BDT as rigid π-conjugated spacers, which have so far been very little studied for dye-sensitized solar cell (DSSC) applications. DFT/TDDFT calculations have been employed to guide the design of the chromophores as well as to shed light on their electronic and optical properties. Photophysical and electrochemical characterization studies have been carried out to gather information on the charge transfer processes occurring at the dye–semiconductor interfaces. Under standard AM 1.5 conditions, DSSC sensitized with CR29 showed good conversion efficiencies: 5.14 % in the liquid electrolyte cell setup and 2.47 % in the solid-state DSSC.

One of the most fascinating characteristics of perovskite solar cells (PSCs) is the retrieved obtainment of outstanding photovoltaic (PV) performances withstanding important device configuration variations. Here we have analyzed CH3NH3PbI3–xClx in planar or in mesostructured (MS) configurations, employing both titania and alumina scaffolds, fully infiltrated with perovskite material or presenting an overstanding layer. The use of the MS scaffold induces to the perovskite different structural properties, in terms of grain size, preferential orientation, and unit cell volume, in comparison to the ones of the material grown with no constraints, as we have found out by X-ray diffraction analyses. We have studied the effect of the PSC configuration on photoinduced absorption and time-resolved photoluminescence, complementary techniques that allow studying charge photogeneration and recombination. We have estimated electron diffusion length in the considered configurations observing a decrease when the material is confined in the MS scaffold with respect to a planar architecture. However, the presence of perovskite overlayer allows an overall recovering of long diffusion lengths explaining the record PV performances obtained with a device configuration bearing both the mesostructure and a perovskite overlayer. Our results suggest that performance in devices with perovskite overlayer is mainly ruled by the overlayer, whereas the mesoporous layer influences the contact properties This work was supported by the Universitat Jaume I (Project 12I361.01/1), by Spanish MINECO (MAT2013-47192-C3-1-R), by EFOR (Iniziativa CNR per il Mezzogiorno L. 191/2009 art. 2 comma 44), by PON-MAAT (Project Number: PON02_00563_3316357-CUP B31C12001230005), by PON-FORM@BEYOND-NANO, and by Regione PUGLIA (APQ Reti di Laboratorio, Project “PHOEBUS” cod. 31). The authors gratefully acknowledge Dr. Paolo Perazzelli for fruitful discussion

This paper reports the spectroscopic and electrochemical characterization of two pi-extended D-A-pi-A organic dyes, G1 and G2, along with a comparison with their donor-free congeners, DTB-T and DTB-B. A collection of measurements has been carried out to provide insight into the different processes (injection, regeneration, and recombination) involved in the photovoltaic conversion. The study aims, in particular, at rationalizing how the presence of a bulky triarylamine donor group, along with the modification in the chemical structure of the pi-bridge, influences the operative cycle of dye-sensitized solar cells. We demonstrated that the donor group contributes to the formation of a more robust organic layer uniformly covering the TiO2 surface, thus decreasing unfavorable charge recombination processes. In addition, the presence of the thiophene sulfur atom in one of the dye pi-extensions (G1), by favoring interactions with the triiodide in the electrolyte, triggers detrimental recombination pathways. We conclude from these observations that G2, the sensitizer with a non-thiophene p-extension, possesses the highest photovoltaic performances among the investigated sensitizers.

A spectroscopic investigation focusing on the charge generation and transport in inverted p-type perovskite-based mesoscopic (Ms) solar cells is provided in this report. Nanocrystalline nickel oxide and PCBM are employed respectively as hole transporting scaffold and hole blocking layer to sandwich a perovskite light harvester. An efficient hole transfer process from perovskite to nickel oxide is assessed, through time-resolved photoluminescence and photoinduced absorption analyses, for both the employed absorbing species, namely MAPbI(3-x)Cl(x) and MAPbI(3). A striking relevant difference between p-type and n-type perovskite-based solar cells emerges from the study.

Here we conceive an innovative nanocomposite to endow hybrid perovskites with the easy processability of polymers, providing a tool to control film quality and material crystallinity. We verify that the employed semiconducting polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), controls the self-assembly of CH3NH3PbI3 (MAPbI(3)) crystalline domains and favors the deposition of a very smooth and homogenous layer in one straightforward step. This idea offers a new paradigm for the implementation of polymer/perovskite nanocomposites towards versatile optoelectronic devices combined with the feasibility of mass production. As a proof-of-concept we propose the application of such nanocomposite in polymer solar cell architecture, demonstrating a power conversion efficiency up to 3%, to date the highest reported for MEH-PPV. On-purpose designed polymers are expected to suit the nanocomposite properties for the integration in diverse optoelectronic devices via facile processing condition.

We propose a new approach for converting light energy into electrical energy, based on the photogeneration of nano-dipoles at donor-acceptor interfaces. The nano-dipoles are oriented in space so as to contribute to a collective polarization that induces a potential difference across the material, sandwiched between electrodes. A current is detected in the external circuit upon illumination. Such a device would exploit many advantages of organic semiconductors and get rid of the main limitation, namely transport. We provide a proof of concept and we discuss the ideal limit of the device based on numerical simulations. This provides design guidelines to the achievement of best performances. Simulations show that the proposed device can be an appealing opportunity with giant conversion efficiency provided some technological issues are overcome.

Charge generation and transport in (CH3NH3) Pbl(3-x)Cl(x) sensitized mesostructured solar cells are investigated. A highly efficient charge generation is directly proven by time correlated single photon counting analysis. Photoinduced absorption and transient photo-voltage investigations depict double charge recombination dynamics. To explain the high device performances according to those spectroscopic observations, we suggest the existence of two complementary paths for electron transport, involving either TiO2 or perovskite matrixes.

Charge generation and transport in CH3NH3PbI3-xClx based mesostructured solar cells are investigated. Time correlated single photon counting analysis proves highly efficient charge generation and provides insights on the structural properties of perovskite films. Photoinduced absorption and transient photovoltage analyses depict a double charge recombination dynamics suggesting the existence of two complementary paths for electron transport, involving either TiO2 and perovskite matrixes. Stark spectroscopy, a powerful tool allowing interface-sensitive analysis, is employed to prove the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer close to the oxide surface. This evidence is also confirmed by first principle DFT calculations. The existence of a structural order, promoted by specific local interactions, could be one of the decisive reasons for highly efficient carriers transport within perovskite films.

To unveil the mechanisms controlling photovoltaic conversion in high-performing perovskite-based meso-structured solar cells, we focus on the key role played by the mesoporous oxide/perovskite interface. We employ several spectroscopic techniques to design a complete scenario and corroborate our results with first principle density functional theory calculations. In particular Stark spectroscopy, a powerful tool allowing interface-sensitive analysis is employed to prove the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer, close to the oxide surface. The existence of a structural order, promoted by specific local interactions, could be one of the decisive reasons for highly efficient carriers transport within perovskite films.

Dye-sensitized solar cells (DSCs) have a typical sandwich structure, with the active layers between two conductive glass sheets. Their co-planarity could be an issue in the mass production of large area devices. The micrometric gap should be uniform all over the device, in order to maintain a good electrolyte layer. The frames of sealant, which isolate the adjacent cells in a module, usually work also as spacers. Nevertheless, the uniformity of the gap is not commonly tested in a systematic way. Here large area empty blanks and full DSCs were studied by means of optical interferometry, i.e., monochromatic surface scan and wavelength scan. The collected fringe patterns allowed retrieval of the microchamber’s absolute profile. In some cases, evident U-shaped bending was found, with edge-to-center variation up to Δ h / h ≈ 80%. Interestingly, despite the large absorption and the weak index contrast in the full DSCs, a good fringes’ visibility was achieved, by adopting near-infrared (IR) laser source and filtering off external reflections. Moreover, the IR n and k indexes of porous titania dyed and filled with electrolyte were retrieved. In summary, the results show that the bending effect must always be tackled for large area, by using the right sealing frames and thermal treatments. Further improved IR interferometry can be successfully implemented for in-line testing of DSCs structure and uniformity.