Panchromatic symmetrical squaraines: a step forward in the molecular engineering of low cost blue-greenish sensitizers for dye-sensitized solar cells.

Two novel symmetrical blue squaraine sensitizers were synthesized, which exhibit panchromatic light harvesting and a record efficiency over 6% with Jsc exceeding 14 mA cm(-2), and Voc over 620 mV under 1 sun. Their color, low cost, easiness of synthesis, and relatively high photo- and thermal stability open up the way for commercial applications.

Cation-induced band-gap tuning in organohalide perovskites: interplay of spin-orbit coupling and octahedra tilting.

Organohalide lead perovskites have revolutionized the scenario of emerging photovoltaic technologies. The prototype MAPbI3 perovskite (MA = CH3NH3(+)) has dominated the field, despite only harvesting photons above 750 nm (∼1.6 eV). Intensive research efforts are being devoted to find new perovskites with red-shifted absorption onset, along with good charge transport properties. Recently, a new perovskite based on the formamidinium cation ((NH2)2CH(+) = FA) has shown potentially superior properties in terms of band gap and charge transport compared to MAPbI3. The results have been interpreted in terms of the cation size, with the larger FA cation expectedly delivering reduced band-gaps in Pb-based perovskites. To provide a full understanding of the interplay among size, structure, and organic/inorganic interactions in determining the properties of APbI3 perovskites, in view of designing new materials and fully exploiting them for solar cells applications, we report a fully first-principles investigation on APbI3 perovskites with A = Cs(+), MA, and FA. Our results evidence that the tetragonal-to-quasi cubic structural evolution observed when moving from MA to FA is due to the interplay of size effects and enhanced hydrogen bonding between the FA cations and the inorganic matrix altering the covalent/ionic character of Pb-I bonds. Most notably, the observed cation-induced structural variability promotes markedly different electronic and optical properties in the MAPbI3 and FAPbI3 perovskites, mediated by the different spin-orbit coupling, leading to improved charge transport and red-shifted absorption in FAPbI3 and in general in pseudocubic structures. Our theoretical model constitutes the basis for the rationale design of new and more efficient organohalide perovskites for solar cells applications.

Adapting Ruthenium Sensitizers to Cobalt Electrolyte Systems.

In this work, we report the use of bulky substitutions in a new heteroleptic ruthenium(II) bipyridine complex, Ru(NCS)2LL', coded TT-230 to obtain high open-circuit potential in a dye-sensitized solar cell (where L is a bipyridine ligand appended with two cyclopenta(2,1-b;3,4-bA)dithiophene moieties, and L' = 4,4,'-dicarboxylic acid 2,2'-bipyridine). The electrolytes based on cobalt complexes have shown significant advantages in terms of attainable open-circuit potential compared to the standard iodide/tri-iodide redox mediators. These merits of the cobalt complexes were previously realized with a porphyrin sensitizer, achieving a VOC greater than 1 V in DSC. However, with conventional Ru(II)-polypyridyl complexes such as the C101 dye, similar increase in the VOC could not be attained due to the enhanced recombination. In this work, we have shown that the use of bulky substituents can prevent the back reaction of photogenerated electron and subsequently increase the open-circuit potential of the device. The recombination processes were investigated by transient photovoltage decay measurements.

Mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cells.

We report for the first time on a hole conductor-free mesoscopic methylammonium lead iodide (CH(3)NH(3)PbI(3)) perovskite/TiO(2) heterojunction solar cell, produced by deposition of perovskite nanoparticles from a solution of CH(3)NH(3)I and PbI(2) in γ-butyrolactone on a 400 nm thick film of TiO(2) (anatase) nanosheets exposing (001) facets. A gold film was evaporated on top of the CH(3)NH(3)PbI(3) as a back contact. Importantly, the CH(3)NH(3)PbI(3) nanoparticles assume here simultaneously the roles of both light harvester and hole conductor, rendering superfluous the use of an additional hole transporting material. The simple mesoscopic CH(3)NH(3)PbI(3)/TiO(2) heterojunction solar cell shows impressive photovoltaic performance, with short-circuit photocurrent J(sc)= 16.1 mA/cm(2), open-circuit photovoltage V(oc) = 0.631 V, and a fill factor FF = 0.57, corresponding to a light to electric power conversion efficiency (PCE) of 5.5% under standard AM 1.5 solar light of 1000 W/m(2) intensity. At a lower light intensity of 100W/m(2), a PCE of 7.3% was measured. The advent of such simple solution-processed mesoscopic heterojunction solar cells paves the way to realize low-cost, high-efficiency solar cells.

A structural study of DPP-based sensitizers for DSC applications.

Four D-π-A sensitizers comprising a thienyl-diketopyrrolopyrrole (ThDPP) bridge were synthesized and tested in iodide/triiodide liquid electrolyte DSC devices. The dye series was strategically designed to develop a structure-property relationship. The best performing sensitizer utilized a phenyl-based anchor and triphenylamine donor (η = 5.03%).

High efficiency quantum dot heterojunction solar cell using anatase (001) TiO2 nanosheets.

This is the first report of using anatase TiO(2) nanosheets with exposed (001) facets in a high-efficiency PbS quantum dot/TiO(2) heterojunction solar cell. The TiO(2) nanosheets have higher conduction band, and surface energy compared to normal anatase (101) TiO(2) nanoparticles. This PbS QD/TiO(2) heterojunction solar cell produces power conversion efficiency of 4.7% which is one of the highest reported in literature.

Self-assembled photosystem-I biophotovoltaics on nanostructured TiO(2 )and ZnO.

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(2) and photocurrent density of 362 µA/cm(2), over four orders of magnitude higher than any photosystem-based biophotovoltaic to date.

A cobalt complex redox shuttle for dye-sensitized solar cells with high open-circuit potentials.

Dye-sensitized solar cells are a promising alternative to traditional inorganic semiconductor-based solar cells. Here we report an open-circuit voltage of over 1,000 mV in mesoscopic dye-sensitized solar cells incorporating a molecularly engineered cobalt complex as redox mediator. Cobalt complexes have negligible absorption in the visible region of the solar spectrum, and their redox properties can be tuned in a controlled fashion by selecting suitable donor/acceptor substituents on the ligand. This approach offers an attractive alternate to the traditional I(3)(-)/I(-) redox shuttle used in dye-sensitized solar cells. A cobalt complex using tridendate ligands [Co(bpy-pz)(2)](3+/2+)(PF(6))(3/2) as redox mediator in combination with a cyclopentadithiophene-bridged donor-acceptor dye (Y123), adsorbed on TiO(2), yielded a power conversion efficiency of over 10% at 100 mW cm(-2). This result indicates that the molecularly engineered cobalt redox shuttle is a legitimate alternative to the commonly used I(3)(-)/I(-) redox shuttle.

Symmetric vs. asymmetric squaraines as photosensitisers in mesoscopic injection solar cells: a structure-property relationship study.

A symmetric squaraine and its related non-symmetric structure are shown to have comparable efficiencies in DSCs, but with undoubtedly advantages in the low cost and easiness of synthesis for the symmetrical structure.

Evaluation of a ruthenium oxyquinolate architecture for dye-sensitized solar cells.

Synthesis of the [Ru(dcbpy)(2)(OQN)](+) complex is reported in which dcbpy and OQN(-) are the bidentate 4,4'-dicarboxy-2,2'-bipyridyl and 8-oxyquinolate ligands, respectively. Spectroscopic, electrochemical, and theoretical analyses are indicative of extensive Ru(OQN) molecular orbital overlap due to degenerate Ru d(π) and OQN p(π) mixing. [Ru(dcbpy)(2)(OQN)](+) displays spectroscopic properties remarkably similar to those of the N3 dye, making it a promising candidate for application in dye-sensitized solar cell devices. However, its solar power conversion efficiency requires further optimization.

Toward interaction of sensitizer and functional moieties in hole-transporting materials for efficient semiconductor-sensitized solar cells.

Sb(2)S(3)-sensitized mesoporous-TiO(2) solar cells using several conjugated polymers as hole-transporting materials (HTMs) are fabricated. We found that the cell performance was strongly correlated with the chemical interaction at the interface of Sb(2)S(3) as sensitizer and the HTMs through the thiophene moieties, which led to a higher fill factor (FF), open-circuit voltage (V(oc)), and short-circuit current density (J(sc)). With the application of PCPDTBT (poly(2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)) as a HTM in a Sb(2)S(3)-sensitized solar cell, overall power conversion efficiencies of 6.18, 6.57, and 6.53% at 100, 50, and 10% solar irradiation, respectively, were achieved with a metal mask.

Design and development of novel linker for PbS quantum dots/TiO2 mesoscopic solar cell.

A novel bifunctional linker molecule, bis(4-mercaptophenyl)phosphinic acid, is designed to be used in a QDs solar cells. The linker anchors to TiO(2) mesoporous film through the phosphinic acid functional group and to the PbS QDs through the two thiol groups. The way of attachment of this new linker molecule in a photovoltaic PbS QDs/TiO(2) mesoporous device was studied by FTIR measurements. The photovoltaic performance of this new linker in a heterojunction PbS QDs solar cell show high V(oc) relative to QDs based solar cells, which will allow to receive high power conversion efficiency using this novel designed linker. This novel bifunctional linker molecule should pave the way for enhancing binding strength, and efficiency of QDs solar cells compared to the state-of-the-art linkers.

CdSe quantum dot (QD) and molecular dye hybrid sensitizers for TiO2 mesoporous solar cells: working together with a common hole carrier of cobalt complexes.

Redox couples based on cobalt complexes were found to be effective in regenerating both inorganic CdSe quantum dot- and organic dye-sensitizers. The hybrid sensitizer composed of CdSe QD and ruthenium sensitizer (Z907Na) dye showed a maximum power conversion efficiency of 4.76% on using cobalt(o-phen)(3)(2+/3+) as a common redox mediator.

Novel luminescent Ir(III) dyes for developing highly sensitive oxygen sensing films.

New sensing films have been developed for the detection of molecular oxygen. These films are based on luminescent Ir(III) dyes incorporated either into polystyrene (with and without plasticizer) or metal oxide, nanostructured material. The preparation and characterization of each film have been investigated in detail. Due to their high sensitivity for low oxygen concentration, the parameters p(O2) (S=1/2) and DeltaI(1%) have been also evaluated in order to establish the most sensitive membrane for controlling concentrations between 0 and 10% and low oxygen concentrations (lower than 1%), respectively. The results show that the use of nanostructured material increased the sensitivity of the film; the most sensitive membrane for controlling O(2) between 0 and 10% is based on N1001 immobilized in AP200/19 (k(sv)=2848+/-101 bar(-1) and p(O2) (S=1/2)=0.0006), and the complex N969 incorporated into AP200/19 seems to be the most suitable for applications in oxygen trace sensing (DeltaI(1%)=93.13+/-0.13%).

High-performance nanostructured inorganic-organic heterojunction solar cells.

We report all solid-state nanostructured inorganic-organic heterojunction solar cells fabricated by depositing Sb(2)S(3) and poly(3-hexylthiophene) (P3HT) on the surface of a mesoporous TiO(2) layer, where Sb(2)S(3) acts as an absorbing semiconductor and P3HT acts as both a hole conductor and light absorber. These inorganic-organic light harvesters perform remarkably well with a maximum incident-photon-to-current efficiency (IPCE) of 80% and power conversion efficiency of 5.13% under air-mass 1.5 global (AM 1.5G) illumination with the intensity of 100 mW cm(-2). These devices are highly stable under room light in air, even without encapsulation. The present findings offer novel directions for achieving high-efficiency solid-state solar cells by hybridization of inorganic-organic light harvesters and hole transporters.

Dual-emitting Langmuir-Blodgett film-based organic light-emitting diodes.

Langmuir-Blodgett (LB) films containing alternating layers of the metallosurfactants bis(4,4'-tridecyl-2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium(II)-bis(chloride) (1) and bis[2-(2,4-difluorophenyl)pyridine](4,4'-dinonadecyl-2,2'-bipyridine)iridium(III) chloride (2) have been prepared. Langmuir monolayers at the air-water interface of 1 and 2 with different anions in the subphase have been characterized by pi-A compression isotherms and Brewster angle microscopy (BAM). The transferred LB films have been characterized by IR, UV-vis and emission spectroscopy, and atomic force microscopy (AFM). Electroluminescent devices formed by LB films containing alternating layers of these two molecules show dual emission by simple mixing of the two emitters in a single LB film, and by preparing two stacked configurations, in which a LB layer of the ruthenium complexes is deposited on top of a LB layer of the iridium complexes and the inverse situation. The color of the electroluminescence can be tuned by changing the thickness of each LB layer. Due to efficient hole blocking of a layer of the iridium complexes when deposited on top of the layer of ruthenium complexes, in that configuration the green emission of the iridium complexes is suppressed. In the opposite case, excitons are generated in both layers although most likely preferentially in the layer of the iridium complexes.

High molar extinction coefficient organic sensitizers for efficient dye-sensitized solar cells.

We have designed and synthesized highly efficient organic sensitizers with a planar thienothiophene-vinylene-thienothiophene linker. Under standard global AM 1.5 solar conditions, the JK-113-sensitized cell gave a short circuit photocurrent density (J(sc)) of 17.61 mA cm(-2), an open-circuit voltage (V(oc)) of 0.71 V, and a fill factor (FF) of 72%, corresponding to an overall conversion efficiency (eta) of 9.1%. The incident monochromatic photo-to-current conversion efficiency (IPCE) of JK-113 exceeds 80% over the spectral region from 400 to 640 nm, reaching its maximum of 93% at 475 nm. The band tails off toward 770 nm, contributing to the broad spectral light harvesting. Solar-cell devices based on the sensitizer JK-113 in conjunction with a volatile electrolyte and a solvent-free ionic liquid electrolyte gave high conversion efficiencies of 9.1% and 7.9%, respectively. The JK-113-based solar cell fabricated using a solvent-free ionic liquid electrolyte showed excellent stability under light soaking at 60 degrees C for 1000 h.

Design and synthesis of a novel anchoring ligand for highly efficient thin film dye-sensitized solar cells.

A novel ligand, 5,5'-(2,2'-bipyridine-4,4'-diyl)-bis(thiophene-2-carboxylic acid) (BTC), and its Ru(II) complex (BTC-1) in which the anchoring group is attached to the thiophene units were developed. Using a low-volatility electrolyte and 3.3 mum mesoporous TiO2 films BTC-1 achieved a solar-to-electricity conversion efficiency of 6.1%, compared to 4.8% for N719 under the same experimental conditions.

Efficient CdSe quantum dot-sensitized solar cells prepared by an improved successive ionic layer adsorption and reaction process.

In pursuit of efficient quantum dot (QD)-sensitized solar cells based on mesoporous TiO(2) photoanodes, a new procedure for preparing selenide (Se(2-)) was developed and used for depositing CdSe QDs in situ over TiO(2) mesopores by the successive ionic layer adsorption and reaction (SILAR) process in ethanol. The sizes and density of CdSe QDs over TiO(2) were controlled by the number of SILAR cycles applied. After some optimization of these QD-sensitized TiO(2) films in regenerative photoelectrochemical cells using a cobalt redox couple [Co(o-phen)(3)(2+/3+)], including addition of a final layer of CdTe, over 4% overall efficiencies were achieved at 100 W/m(2) with about 50% IPCE at its maximum. Light-harvesting properties and transient voltage decay/impedance measurements confirmed that CdTe-terminated CdSe QD cells gave better charge-collection efficiencies and kinetic parameters than corresponding CdSe QD cells. In a preliminary study, a CdSe(Te) QD-sensitized TiO(2) film was combined with an organic hole conductor, spiro-OMeTAD, and shown to exhibit a promising efficiency of 1.6% at 100 W/m(2) in inorganic/organic hybrid all-solid-state cells.

White-light phosphorescence emission from a single molecule: application to OLED.

A simple mononuclear cyclometallated iridium(iii) complex exhibits white photo- and electro- luminescence in the wavelength range from 440 to 800 nm, which originates from a single emitting excited state of mixed character.