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The effective defect passivation of metal halide perovskite (MHP) surfaces is a key strategy to simultaneously tackle MHP solar cell performances enhancement and their stability under operative conditions. Plasma‐based dry processing is an established methodology for the modification of materials surfaces as it does not present the disadvantages often associated with wet treatments. This is becoming a fine tool to reach precise atomic‐scale engineering of the MHP surfaces. Herein is reported a comprehensive picture of the interaction between different plasma chemistries and MHP thin films. The impact of Ar, H2, N2, and O2 low‐pressure plasmas on MHP optochemical properties and morphology is correlated with the performance of photovoltaic devices and rationalized by density functional theory calculations. Strong morphological modifications and selective removal of the uppermost methylammonium moieties are deemed responsible for nonradiative surface defects suppression and higher solar cell performances. Ellipsometry and X‐ray photoelectron spectroscopies shine light on the subtle modifications induced by the different plasma environments, paving the way for the more effective engineering of plasma‐based (deposition) processing. Notably, for O2 plasma treatment, deep‐state traps induced by the formation of IO4− species are demonstrated and rationalized, highlighting the challenges in optimizing O2 plasma‐based solutions for MHP‐based devices. [ABSTRACT FROM AUTHOR]

The prevalence of background hole doping in tin halide perovskites usually dominates their recombination dynamics. The addition of excess Sn halide source to the precursor solution is the most frequently used approach to reduce the hole doping and reveals photo‐carrier dynamics related to defects activity. This study presents an experimental and theoretical investigation on defects under light irradiation in tin halide perovskites by combining measurements of photoluminescence with first principles computational modeling. It finds that tin perovskite thin films prepared with an excess of Sn halide sources exhibit an enhancement of the photoluminescence intensity over time under continuous excitation in inert atmosphere. The authors propose a model in which light irradiation promotes the annihilation of VSn2−/Sni2+ Frenkel pairs, reducing the deep carrier trapping centers associated with such defect and increasing the radiative recombination. Importantly, these observations can be traced in the open‐circuit voltage dynamics of tin‐based halide perovskite solar cells, implying the relevance of controlling the Sn photochemistry to stabilize tin perovskite devices. [ABSTRACT FROM AUTHOR]

Perovskite semiconductors are an attractive option to overcome the limitations of established silicon based photovoltaic (PV) technologies due to their exceptional opto‐electronic properties and their successful integration into multijunction cells. However, the performance of single‐ and multijunction cells is largely limited by significant nonradiative recombination at the perovskite/organic electron transport layer junctions. In this work, the cause of interfacial recombination at the perovskite/C60 interface is revealed via a combination of photoluminescence, photoelectron spectroscopy, and first‐principle numerical simulations. It is found that the most significant contribution to the total C60‐induced recombination loss occurs within the first monolayer of C60, rather than in the bulk of C60 or at the perovskite surface. The experiments show that the C60 molecules act as deep trap states when in direct contact with the perovskite. It is further demonstrated that by reducing the surface coverage of C60, the radiative efficiency of the bare perovskite layer can be retained. The findings of this work pave the way toward overcoming one of the most critical remaining performance losses in perovskite solar cells. [ABSTRACT FROM AUTHOR]

Methylammonium lead iodide perovskite (MAPbI3) is today considered the most promising component for highly efficient third generation solar cells. However, the lifetime of the solar devices is strongly affected by the stability of the MAPbI3 films toward humidity, UV irradiation, and temperature. The search for efficient protective additives to be used for building up composite perovskite films with enhanced stability is a topic of great interest in the scientific community. In the present paper, a layered zirconium phosphate‐phosphonate based on N,N‐phosphonomethylglycine, exfoliated in thin nanosheets (NS), as additive for the stabilization of MAPbI3 crystalline films toward humidity, UV‐irradiation, and temperature changes is applied. Notably, the additive is extremely efficient in preventing degradation of the perovskite film, preserving the optical and structural properties, and avoiding the phase transitions normally observed due to temperature increase. [ABSTRACT FROM AUTHOR]

Organic halide salt passivation is considered to be an essential strategy to reduce defects in state-of-the-art perovskite solar cells (PSCs). This strategy, however, suffers from the inevitable formation of in-plane favored two-dimensional (2D) perovskite layers with impaired charge transport, especially under thermal conditions, impeding photovoltaic performance and device scale-up. To overcome this limitation, we studied the energy barrier of 2D perovskite formation from ortho-, meta- and para-isomers of (phenylene)di(ethylammonium) iodide (PDEAI2) that were designed for tailored defect passivation. Treatment with the most sterically hindered ortho-isomer not only prevents the formation of surficial 2D perovskite film, even at elevated temperatures, but also maximizes the passivation effect on both shallow- and deep-level defects. The ensuing PSCs achieve an efficiency of 23.9% with long-term operational stability (over 1000 h). Importantly, a record efficiency of 21.4% for the perovskite module with an active area of 26 cm2 was achieved. Salt passivation of perovskite often results in formation of 2D perovskite layers, which impaired charge transport behaviour. Here, the authors study the energy barrier of 2D perovskite formation upon passivation by different iodide salt, and provide insight how to manipulate this to maximise device performance. [ABSTRACT FROM AUTHOR]

Interfaces play a crucial role in determining perovskite solar cells, (PSCs) performance and stability. It is therefore of great importance to constantly work toward improving their design. This study shows the advantages of using a hole‐transport material (HTM) that can anchor to the perovskite surface through halogen bonding (XB). A halo‐functional HTM (PFI) is compared to a reference HTM (PF), identical in optoelectronic properties and chemical structure but lacking the ability to form XB. The interaction between PFI and perovskite is supported by simulations and experiments. XB allows the HTM to create an ordered and homogenous layer on the perovskite surface, thus improving the perovskite/HTM interface and its energy level alignment. Thanks to the compact and ordered interface, PFI displays increased resistance to solvent exposure compared to its not‐interacting counterpart. Moreover, PFI devices show suppressed nonradiative recombination and reduced hysteresis, with a Voc enhancement of ≥20 mV and a remarkable stability, retaining more than 90% efficiency after 550 h of continuous maximum‐power‐point tracking. This work highlights the potential that XB can bring to the context of PSCs, paving the way for a new halo‐functional design strategy for charge‐transport layers, which tackles the challenges of charge transport and interface improvement simultaneously. [ABSTRACT FROM AUTHOR]

Surface passivation treatment is a widely used strategy to resolve trap‐mediated nonradiative recombination toward high‐efficiency metal‐halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in‐depth understanding of its passivation mechanism. Here, a systematic study on a mixed‐salt passivation strategy of formamidinium bromide (FABr) coupled with different F‐substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F‐substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed‐salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI2. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high‐quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed‐salt treatment. In addition, the introduction of the moisture resisted F‐substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long‐term stability under a high humid atmosphere as well as operational conditions. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have raised huge excitement in the field of emerging photovoltaic technologies. The possibility of fabricating perovskite solar cells (PSCs) on lightweight, flexible substrates, with facile processing methods, provides very attractive commercial possibilities. Nevertheless, efficiency values for flexible devices reported in the literature typically fall short in comparison to rigid, glass‐based architectures. Here, a solution‐processable fullerene derivative, [6,6]‐phenyl‐C61 butyric acid n‐hexyl ester (PCBC6), is reported as a highly efficient alternative to the commonly used n‐type materials in perovskite solar cells. The cells with the PCBC6 layer deliver a power conversion efficiency of 18.4%, fabricated on a polymer foil, with an active area of 1 cm2. Compared to the phenyl‐C61‐butyric acid methyl ester benchmark, significantly enhanced photovoltaic performance is obtained, which is primarily attributed to the improved layer morphology. It results in a better charge extraction and reduced nonradiative recombination at the perovskite/electron transporting material interface. Solution‐processed PCBC6 films are uniform, smooth and displayed conformal capping of perovskite layer. Additionally, a scalable processing of PCBC6 layers is demonstrated with an ink‐jet printing technique, producing flexible PSCs with efficiencies exceeding 17%, which highlights the prospects of using this material in an industrial process. [ABSTRACT FROM AUTHOR]

The peculiar optoelectronic properties of metal‐halide perovskites, partly underlying their success in solar cells and light emitting devices, are likely related to the complex interplay of electronic and structural features mediated by formation of polarons. In this paper the current status of polaron physics in metal‐halide perovskites is reviewed based on a first‐principles computational perspective, which has delivered hitherto noaccessible insights into the electronic and structural features associated with polaron formation in this materials class. The role of organic (dipolar) versus inorganic (spherical) A‐site cations is extensively analyzed, these cations are related to modulation of the energetics and structural extension of polarons in lead‐halide perovskites. Further tuning of polaron energetics is achieved by individual variations in metal (e.g., Pb → Sn) and halide (e.g., I → Br), showing a transition from a semilocalized to a localized polaron regime in which charge holes can be trapped at isolated Sn centers. The vastly varying and tunable nature of charge lattice interactions represents a peculiarity of metal‐halide perovskites that should be taken into account when designing novel materials or targeting specific compositional engineering of existing perovskites. [ABSTRACT FROM AUTHOR]

Abstract: Despite the need of a reliable technology for solar energy harvesting, research on new materials for third generation photovoltaics is slowed down by the diffuse use of trial and error rather than rational material design approaches. The proposed study investigates the use of alternative strategies to material discovery inspired by drug design and molecular modeling. In particular, training set and test set (for validation purposes) comprising well‐known small molecule‐bulk heterojunction organic photovoltaics were built. Molecules were characterized by semiempirical calculated and 3D molecular interaction fields–based descriptors. Then partial least squares algorithm was applied to rationalize structure‐photovoltaic activity relationships, and coefficients were investigated to clarify contributions played by the different molecular properties to the final performance. In addition, a photovoltaic desirability function (PhotD) was also proposed as alternative and versatile novel tool for ranking potential candidates. The partial least squares model and PhotD function were both internally and externally validated demonstrating their ability in estimating new candidates performances. The proposed approach demonstrates that, in the context of computational materials science, chemometrics and molecular modeling tools could effectively boost the discovery of novel promising candidates for photovoltaic application. [ABSTRACT FROM AUTHOR]

The article discusses the theoretical studies on phases of anatase and less common titanium dioxide. Topics covered include electronic properties of bulk anatase, character of electron and holes states in anatase, and surface modification. Also mentioned are its applications in photocatalysis and hybrid/organic solar cells, and its less common polymorphs like brookite.

Two thiocyanate-free ruthenium(II) sensitizers, TFRS-41 and TFRS-42, with distinctive dialkoxyphenyl thienyl substituents were successfully prepared and tested for potential applications in making dye-sensitized solar cells (DSCs). Subsequent device fabrication was conducted by using a [Co(bpy)3]2+/3+-based (bpy=2,2′-bipyridine) electrolyte, for which the best performance data, namely, JSC=13.11 mA cm−2, VOC=862 mV, fill factor=0.771, and η=8.71 %, were recorded for the sensitizer TFRS-42 with a 2,6-dialkoxyphenyl substituent under AM 1.5G irradiation. The markedly higher Voc value was confirmed by the longer electron lifetime revealed in transient photovoltage (TPV) measurements versus the TFRS-1 sensitizer. In addition, DFT calculation and detailed first-principles computational analysis were conducted to provide a rationale for the observed trends in their photovoltaic performances and electron lifetimes, with reference to different performances exhibited by three thiocyanate-free sensitizers, TFRS-1, TFRS-41 and TFRS-42, versus Z907 reference. Through the proper control of peripheral substituents, the thiocyanate-free ruthenium(II)-based DSC sensitizers can positively influence the performances of DSCs, with better light-harvesting capability and suppressed charge recombination, for DSC cells fabricated by using a [Co(bpy)3]2+/3+-based electrolyte. [ABSTRACT FROM AUTHOR]

Hybrid AMX3 perovskites (A = Cs, CH3NH3; M = Sn, Pb; X = halide) have revolutionized the scenario of emerging photovoltaic technologies, with very recent results demonstrating 15% efficient solar cells. The CH3NH3PbI3/MAPb(I1-xClx)3 perovskites have dominated the field, while the similar CH3NH3SnI3 has not been exploited for photovoltaic applications. Replacement of Pb by Sn would facilitate the large uptake of perovskite-based photovoltaics. Despite the extremely fast progress, the materials electronic properties which are key to the photovoltaic performance are relatively little understood. Density Functional Theory electronic structure methods have so far delivered an unbalanced description of Pb- and Sn-based perovskites. Here we develop an effective GW method incorporating spin-orbit coupling which allows us to accurately model the electronic, optical and transport properties of CH3NH3SnI3 and CH3NH3PbI3, opening the way to new materials design. The different CH3NH3SnI3 and CH3NH3PbI3 electronic properties are discussed in light of their exploitation for solar cells, and found to be dominantly due to relativistic effects. These effects stabilize the CH3NH3PbI3 material towards oxidation, by inducing a deeper valence band edge. Relativistic effects, however, also increase the material band-gap compared to CH3NH3SnI3, due to the valence band energy downshift (∼0.7 eV) being only partly compensated by the conduction band downshift (∼0.2 eV). [ABSTRACT FROM AUTHOR]

We report a facile synthetic route to obtain functionalized quaterpyridine ligand and its trans-dithiocyanato ruthenium complex, based on a microwave-assisted procedure. The ruthenium complex has been purified using a silica chromatographic column by protecting carboxylic acid groups as iso-butyl ester, which are subsequently hydrolyzed. The highly pure complex exhibits panchromatic response throughout the visible region. DFT/time-dependent DFT calculations have been performed on the ruthenium complex in solution and adsorbed onto TiO2 to analyze relative electronic and optical properties. The ruthenium complex endowed with the functionalized quaterpyridine ligand was used as a sensitizer in dye-sensitized solar cell yielding a short-circuit photocurrent density of more than 19 mA cm−2 with a broad incident photon to current conversion efficiency spectra ranging from 400 to 900 nm, exceeding 80 % at 700 nm. [ABSTRACT FROM AUTHOR]

A facile and fast approach, based on microwave-enhanced Sonogashira coupling, has been employed to obtain in good yields both mono- and, for the first time, disubstituted push-pull ZnII porphyrinates bearing a variety of ethynylphenyl moieties at the β-pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β-mono- or disubstituted ZnII porphyrinates and meso-disubstituted push-pull ZnII porphyrinates. We have obtained evidence that, although the HOMO-LUMO energy gap of the meso-substituted push-pull dyes is lower, so that charge transfer along the push-pull system therein is easier, the β-mono- or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β-monosubstituted porphyrinic dye interacting with a TiO2 surface and by the positive effect of the β substitution on the incident photon-to-current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350-650 nm). In contrast, meso-substitution produces IPCE spectra with two less intense and well-separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge-transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β-monosubstituted ZnII porphyrinates extremely promising sensitizers for use in DSSCs. [ABSTRACT FROM AUTHOR]

An organic dye-sensitized solar cell consisting of a squaraine molecule attached to a TiO2 surface is modeled using first-principles molecular dynamics and time-dependent density functional theory. The system is surrounded by solvent molecules that are treated at the same level of theory as the dye molecule and the surface. The effect of the solvent on optical properties is investigated by computing many absorption spectra for various configurations along a molecular dynamics trajectory. It is shown that the dynamical effects induced by thermal fluctuations have a strong effect on the optical properties and that satisfactory agreement with experiments is achieved only when those thermal effects are accounted for explicitly. [ABSTRACT FROM AUTHOR]

We report a combined experimental and computational study of several ruthenium(II) sensitizers originated from the [Ru(dcbpyH2)2(NCS)2], N3, and [Ru(dcbpyH2)(tdbpy)(NCS)2], N621, (dcbpyH2 = 4,4'- dicarboxy-2,2'-bipyridine, tdbpy = 4,4'-tridecyl-2,2'-bipyridine) complexes. A purification procedure was developed to obtain pure N-bonded isomers of both types of sensitizers. The photovoltaic data of the purified N3 and N621 sensitizers adsorbed on TiO2 films in their monoprotonated and diprotonated state, exhibited remarkable power conversion efficiency at 1 sun, 11.18 and 9.57%, respectively. An extensive Density Functional Theory (DFT)-Time Dependent DFT study of these sensitizers in solution was performed, investigating the effect of protonation of the terminal carboxylic groups and of the counterions on the electronic structure and optical properties of the dyes. The calculated absorption spectra are in good agreement with the experiment, thus allowing a detailed assignment of the UV-vis spectral features of the two types of dyes. The computed alignments of the molecular orbitals of the different complexes with the band edges of a model TiO2 nanoparticle provide additional insights into the electronic factors governing the efficiency of dye-sensitized solar cell devices. [ABSTRACT FROM AUTHOR]

Two new hole selective materials (HSMs) based on dangling methylsulfanyl groups connected to the C‐9 position of the fluorene core are synthesized and applied in perovskite solar cells. Being structurally similar to a half of Spiro‐OMeTAD molecule, these HSMs (referred as FS and DFS) share similar redox potentials but are endowed with slightly higher hole mobility, due to the planarity and large extension of their structure. Competitive power conversion efficiency (up to 18.6%) is achieved by using the new HSMs in suitable perovskite solar cells. Time‐resolved photoluminescence decay measurements and electrochemical impedance spectroscopy show more efficient charge extraction at the HSM/perovskite interface with respect to Spiro‐OMeTAD, which is reflected in higher photocurrents exhibited by DFS/FS‐integrated perovskite solar cells. Density functional theory simulations reveal that the interactions of methylammonium with methylsulfanyl groups in DFS/FS strengthen their electrostatic attraction with the perovskite surface, providing an additional path for hole extraction compared to the sole presence of methoxy groups in Spiro‐OMeTAD. Importantly, the low‐cost synthesis of FS makes it significantly attractive for the future commercialization of perovskite solar cells. [ABSTRACT FROM AUTHOR]

A solution of MeNH3PbI3 in γ-butyrolactone is prepared from an equimolar mixture of MeNH3I and PbI2 and solutions of MeNH3PbI3-xClx in anhydrous DMF are obtained from MeNH3I and PbCl2 (3:1 molar ratio) and MeNH3Cl and PbI2 (1:1 molar ratio). [ABSTRACT FROM AUTHOR]

Protecting organohalide perovskitethin films from water and ambienthumidity represents a paramount challenge for the commercial uptakeof perovskite solar cells and, in general, of related optoelectronicdevices. Therefore, understanding the perovskite/water interface isof crucial importance. As a step in this direction, here we present ab initiomolecular dynamics simulations aimed at unravelingthe atomistic details of the interaction between the methylammoniumlead iodide (MAPbI3) perovskite surfaces and a liquid waterenvironment. According to our calculations, MAI-terminated surfacesundergo a rapid solvation process, driven by the interaction of watermolecules with Pb atoms, which prompts the release of I atoms. PbI2-terminated surfaces, instead, seem to be more robust to degradation,by virtue of the stronger (shorter) Pb–I bonds formed on thesefacets. We also observe the incorporation of a water molecule intothe PbI2-terminated slab, which could represent the firststep in the formation of an intermediate hydrated phase. Interestingly,PbI2defects on the PbI2-terminated surfacepromote the rapid dissolution of the exposed facet. Surface hydration,which is spontaneous for both MAI- and PbI2-terminatedslabs, does not modify the electronic landscape of the former, whilethe local band gap of the PbI2-exposing model widens by∼0.3 eV in the interfacial region. Finally, we show that waterincorporation into bulk MAPbI3produces almost no changesin the tetragonal structure of the perovskite crystal (∼1%volume expansion) but slightly opens the band gap. We believe thatthis work, unraveling some of the atomistic details of the perovskite/waterinterface, may inspire new interfacial modifications and device architectureswith increased stabilities, which could in turn assist the commercialuptake of perovskite solar cells and optoelectronic devices. [ABSTRACT FROM AUTHOR]

We report on ab initio electronicstructure and Car–Parrinellomolecular dynamics simulations for several structural models of theprototype MAPbI3perovskite for solar cells applications.We considered both configurations having a preferred orientation ofthe MA cations, giving rise to a net dipole alignment, and configurationswith an isotropic distribution of the MA cations, respectively representativeof polar (ferroelectric) and apolar (antiferroelectric) structures.Our calculations demonstrate the preferred stability of a set of polarstructures over apolar ones, with an energy difference within 0.1eV and a conversion barrier within 0.2 eV per unit cell (four MAPbI3), thus possibly accessible at room temperature. Ferroelectric-likeorientations lead to a quasi I4cmstructure for the inorganic component, characterized by lack ofinversion symmetry, while the antiferroelectric-like orientationsare associated to a quasi I4/mcmstructure. Ab initio molecular dynamics simulations on the polarstructures show no molecular rotations in the investigated time-scale,while several MA rotations are observed in the same time scale forthe considered apolar structure, which is thus characterized by ahigher disorder. The I4cmand I4/mcmtypes of structure have markedlydifferent band structures, despite showing a relatively small bandgap variation. Simulations carried out on finite surface slabs demonstratethat a net orientation of the MA cations gives rise to a strong bendingin the valence and conduction bands, which could definitely assistcharge separation and reduce carrier recombination, provided one isable to effectively stabilize polar compared to apolar structures.We believe our results could contribute an important step toward anin-depth comprehension of the basic properties of organohalide perovskites,assisting a further optimization of their photovoltaic response. [ABSTRACT FROM AUTHOR]

The article explores the application of titanium dioxide nanomaterials in photovoltaic devices. Topics discussed include the configuration and the working principle of the solar cell, the benefits of using nanostructured titanium dioxide materials, and the modulation of properties and the charge transfer of kinetics at the titanium oxide interface. The applications include dye-sensitized solar cells, quantum dot-sensitized solars, and perovskite solar cells.

Compositional engineering of a mixed cation/mixed halide perovskite in the form of (FAPbI3)0.85(MAPbBr3)0.15 is one of the most effective strategies to obtain record-efficiency perovskite solar cells. However, the perovskite self-organization upon crystallization and the final elemental distribution, which are paramount for device optimization, are still poorly understood. Here we map the nanoscale charge carrier and elemental distribution of mixed perovskite films yielding 20% efficient devices. Combining a novel in-house-developed high-resolution helium ion microscope coupled with a secondary ion mass spectrometer (HIM-SIMS) with Kelvin probe force microscopy (KPFM), we demonstrate that part of the mixed perovskite film intrinsically segregates into iodide-rich perovskite nanodomains on a length scale of up to a few hundred nanometers. Thus, the homogeneity of the film is disrupted, leading to a variation in the optical properties at the micrometer scale. Our results provide unprecedented understanding of the nanoscale perovskite composition. [ABSTRACT FROM AUTHOR]

Therapid development of organometal halide perovskite solar cellshas led to reports of power conversion efficiencies of over 20%. Despitethis excellent performance, their instability remains the major challengelimiting their commercialization. In this report, we systematicallyinvestigate the origin of the thermal instability of perovskite solarcells fabricated using ZnO electron transport layers. Through in situgrazing incidence X-ray diffraction experiments and density functionaltheory calculations, we show that the basic nature of the ZnO surfaceleads to proton-transfer reactions at the ZnO/CH3NH3PbI3interface, which results in decompositionof the perovskite film. The decomposition process is accelerated bythe presence of surface hydroxyl groups and/or residual acetate ligands;calcination of the ZnO layer results in a more thermally stable ZnO/CH3NH3PbI3interface, albeit at the costof a small decrease in power conversion efficiency. [ABSTRACT FROM AUTHOR]

Variousdipolar π-delocalized Ru(II) dialkynyl complexeswere prepared and characterized. Their second-order nonlinear optical(NLO) properties were investigated by the electric-field-induced secondharmonic generation (EFISH) technique working in CH2Cl2solution with an incident wavelength of 1907 nm, whereasthe dipole moments were determined by density functional theory (DFT)calculations. All the investigated complexes are characterized bya negative value of μβ1.907 EFISH, inagreement with a negative value of Δμeg(differenceof the dipole moment in the excited and ground state) upon excitation.Their second-order NLO response can be easily modulated by the natureof the alkynyl substituents. Besides, the most promising “push–pull”ruthenium diacetylide complex, adequately functionalized for anchoringto TiO2, was tested as photosensitizer in dye-sensitizedsolar cells (DSSCs). [ABSTRACT FROM AUTHOR]

Organohalide lead perovskites haverevolutionized the scenarioof emerging photovoltaic technologies. The prototype MAPbI3perovskite (MA = CH3NH3+) has dominatedthe field, despite only harvesting photons above 750 nm (∼1.6eV). Intensive research efforts are being devoted to find new perovskiteswith red-shifted absorption onset, along with good charge transportproperties. Recently, a new perovskite based on the formamidiniumcation ((NH2)2CH+= FA) has shownpotentially superior properties in terms of band gap and charge transportcompared to MAPbI3. The results have been interpreted interms of the cation size, with the larger FA cation expectedly deliveringreduced band-gaps in Pb-based perovskites. To provide a full understandingof the interplay among size, structure, and organic/inorganic interactionsin determining the properties of APbI3perovskites, inview of designing new materials and fully exploiting them for solarcells applications, we report a fully first-principles investigationon APbI3perovskites with A = Cs+, MA, and FA.Our results evidence that the tetragonal-to-quasi cubic structuralevolution observed when moving from MA to FA is due to the interplayof size effects and enhanced hydrogen bonding between the FA cationsand the inorganic matrix altering the covalent/ionic character ofPb–I bonds. Most notably, the observed cation-induced structuralvariability promotes markedly different electronic and optical propertiesin the MAPbI3and FAPbI3perovskites, mediatedby the different spin–orbit coupling, leading to improved chargetransport and red-shifted absorption in FAPbI3and in generalin pseudocubic structures. Our theoretical model constitutes the basisfor the rationale design of new and more efficient organohalide perovskitesfor solar cells applications. [ABSTRACT FROM AUTHOR]

Tounveil the mechanisms controlling photovoltaic conversion inhigh-performing perovskite-based mesostructured solar cells, we focuson the key role played by the mesoporous oxide/perovskite interface.We employ several spectroscopic techniques to design a complete scenarioand corroborate our results with first principle density functionaltheory calculations. In particular Stark spectroscopy, a powerfultool allowing interface-sensitive analysis is employed to prove theexistence of oriented permanent dipoles, consistent with the hypothesisof an ordered perovskite layer, close to the oxide surface. The existenceof a structural order, promoted by specific local interactions, couldbe one of the decisive reasons for highly efficient carriers transportwithin perovskite films. [ABSTRACT FROM AUTHOR]

A new general synthetic access to carboxylated quaterpyridines (qpy), of interest as ligands for panchromatic dye-sensitized solar cell organometallic sensitizers, is presented. The strategic step is a Suzuki--Miyaura cross-coupling reaction, which has allowed the preparation of a number of representative unsubstituted and alkyl and (hetero)aromatic substituted qpys. To bypass the poor inherent stability of 2-pyridylboronic acid derivatives, we successfully applied N-methyliminodiacetic acid (MIDA) boronates as key reagents, obtaining the qpy ligands in good yields up to (quasi)gram quantities. The structural, spectroscopic (NMR and UV--vis), electrochemical, and electronic characteristics of the qpy have been experimentally and computationally (DFT) investigated. The easy access to the bis-thiocyanato Ru(II) complex of the parent species of the qpy series, through an efficient route which bypasses the use of Sephadex column chromatography, is shown. The bis-thiocyanato Ru(ll) complex has been spectroscopically (NMR and UV--vis), electrochemically, and computationally investigated, relating its properties to those of previously reported Ru(II)--qpy complexes. [ABSTRACT FROM AUTHOR]

Novel unsymmetrical organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at a molecular level and synthesized for sensitization of mesoscopic titanium dioxide injection solar cells. The unsymmetrical organic sensitizers 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), 3-(5-bis(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D7), 5-(4-(bis(4-methoxyphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D9), and 3-(5-bis(4,4′-dimethoxydiphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D11) anchored onto TiO2 and were tested in dye-sensitized solar cell with a volatile electrolyte. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is above 80%, and D11-sensitized solar cells yield a short-circuit photocurrent density of 13.90 ± 0.2 mA/cm2, an open-circuit voltage of 740 ± 10 mV, and a fill factor of 0.70 ± 0.02, corresponding to an overall conversion efficiency of 7.20% under standard AM 1.5 sun light. Detailed investigations of these sensitizers reveal that the long electron lifetime is responsible for differences in observed open-circuit potential of the cell. As an alternative to liquid electrolyte cells, a solid-state organic hole transporter is used in combination with the D9 sensitizer, which exhibited an efficiency of 3.25%. Density functional theory/time-dependent density functional theory calculations have been employed to gain insight into the electronic structure and excited states of the investigated species. [ABSTRACT FROM AUTHOR]

Novel organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at molecular level and synthesized. The functionalized unsymmetrical organic sensitizers 3-{5-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-thiophene-2-yl}-2-cyano-acrylic acid (JK-1) and 3-{5′-[N,N-bis-(9,9-dimethylfluorene-2-yl)phenyl]-2,2′-bisthiophene-5-yl}-2-cyano-acrylic acid (JK-2), upon anchoring onto TiO2 film, exhibit unprecedented incident photon to current conversion efficiency of 91%. The photovoltaic data using an electrolyte having composition of 0.6 M M-methyl-N-butyl imidiazolium iodide, 0.04 M iodine, 0.025 M Lil, 0.05 M guanidinium thiocyanate, and 0.28 M tert-butylpyridine in a 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 14.0 ± 0.2 mA/cm², an open circuit voltage of 753 ± 10 mV, and a fill factor of 0.76 ± 0.02, corresponding to an overall conversion efficiency of 8.01% under standard AM 1.5 sunlight. DFT/TDDFT calculations have been performed on the two organic sensitizers to gain insight into their structural, electronic, and optical properties. Our results show that the cyanoacrylic acid groups are essentially coplanar with respect to the thiophene units, reflecting the strong conjugation across the thiophene-cyanoacrylic groups. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, while TDDFT calculations allowed assignment of the visible absorption bands. [ABSTRACT FROM AUTHOR]