Full Solution Process of a Near-Infrared Light-Emitting Electrochemical Cell Based on Novel Emissive Ruthenium Complexes of 1,10-Phenanthroline-Derived Ligands and a Eutectic Alloy as the Top Electrode.

Near-infrared luminescent materials have recently received considerable attention for a large number of applications, including in solid-state lighting, as bioimaging agents, as photovoltaic cells, and in the telecommunication industry. By adding diverse electron-donating or withdrawing groups on ancillary ligands based on benzenethiol-phenanthroline, we synthesized and optoelectronically characterized a series of novel ionic ruthenium complexes, namely RuS, RuSCl, RuSMe, and RuSNH2, for using in a light-emitting electrochemical cell. The synthesized complexes are intense red emitters in the range of 584-605 nm in solution, which depends on the substitutions of electron donor/acceptor moieties on the ancillary ligands. To find a suitable quantum mechanical approach, benchmark calculations based on time-dependent density functional theory were carried out on these complexes. Our benchmark revealed that the M06-L method has results close to those of the experiment. Furthermore, to gain a deeper insight into electronic transitions, several excitation processes were investigated at the TD-DFT-SMD-MN12-L/gen level. The results showed that in the designed complexes, the dominant transition is between the 4dZ2 electron of Ru (particle) and the π* orbitals of the ancillary ligand (hole). The single-layer devices, including these complexes along with a Ga/In cathode by a facile deposition method without the addition of any electron or hole transport layers, were fabricated and displayed red (678 nm) to near-infrared (701 nm) emission as well as a decrease of turn-on voltage from 3.85 to 3.10 V. In particular, adding a methyl group to the ancillary ligand in the complex RuSNH2 increases the external quantum efficiency to 0.55%, one of the highest observed values in the ruthenium phenanthroline family. This simple structure of the device lets us develop the practical applications of light-emitting electrochemical cells based on injection and screen-printing methods, which are very promising for the vacuum-free deposition of top electrodes.

The evolution of triphenylamine hole transport materials for efficient perovskite solar cells.

In recent years, the dramatic increase in power conversion efficiency (PCE) coupled with a decrease in the total cost of third-generation solar cells has led to a significant increase in the collaborative research efforts of academic and industrial researchers. Such interdisciplinary studies have afforded novel materials, which in many cases are now ready to be brought to the marketplace. Within this framework, the field of perovskite solar cells (PSCs) is currently an important area of research due to their extraordinary light-harvesting properties. In particular, PSCs prepared via facile synthetic procedures, containing hole transport materials (HTMs) with versatile triphenylamine (TPA) structural cores, amenable to functionalization, have become a focus of intense global research activity. To optimize the efficiency of the solar cells to achieve efficiencies closer to rival silicon-based technology, TPA building blocks must exhibit favourable electrochemical, photophysical, and photochemical properties that can be chemically tuned in a rational manner. Although PSCs based on TPA building blocks exhibit attractive properties such as high-power efficiencies, a reduction in their synthetic costs coupled with higher stabilities and environmental considerations still need to be addressed. Considering the above, a detailed summary of the most promising compounds and current methodologies employed to overcome the remaining challenges in this field is provided. The objective of this review is to provide guidance to readers on exploring new avenues for the discovery of efficient TPA derivatives, to aid in the future development and advancement of TPA-based PSCs for commercial applications.

Versatile Electroluminescence Color-Tuning Strategy of an Efficient Light-Emitting Electrochemical Cell (LEC) by an Ionic Additive.

The color-tuning strategies of solid-state light-emitting devices (ss-LEDs) are mainly focused on engineering molecular structures. In this paper, for the first time, we developed a facile strategy for tuning the electroluminescence (EL) color from orange to green through the addition of the ionic additive TBAP (tetrabutylammonium perchlorate). To achieve the active ionic emissive compound for use in a light-emitting electrochemical cell (LEC), the neutral biscyclometalated bromo tetrazole iridium(III) [Ir(ppy)2(BrTz)] was exchanged to its cationic complex, [Ir(ppy)2(BrTz-Me)]ClO4 (ppy = 2-phenyl pyridine, BrTz = 4-bromo-2-pyridine tetrazole, BrTz-Me = 4-bromo-2-pyridine methyl tetrazole) with a new synthetic strategy. This method allows employing neutral Ir-cyclometalated complexes, which are ruled out for use in LECs because of their non-ionic behaviors. In the following, an LEC based on the new cationic [Ir(ppy)2(BrTz-Me)]ClO4 as the emissive layer was fabricated between the FTO (fluorine-doped tin oxide) anode and Ga:In alloy cathode without using any additive or polymers, which makes this configuration the simplest ss-LED so far. By adding the ionic additives, the electroluminescence characteristics of [Ir(ppy)2(BrTz-Me)]ClO4 were dramatically increased, including luminance (L) from 162.8 cd/m2 for the device with an additive to 212.9 and 355.9 cd/m2 for devices containing LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) and TBAP, respectively. In particular, when TBAP was added to the [Ir(ppy)2(BrTz-Me)]ClO4 complex, the irradiance was significantly increased from 166.4 to 220.8 µW/cm2 with an efficacy of 1.78 cd/A and external quantum efficiency (EQE) value of 2.14%. The obtained EL results clearly showed that adding TBAP and LiTFSI significantly improved the electroluminescence characteristics and tuned the electroluminescence color.

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)-Silver(I) Complex.

Turn-on time is a key factor for lighting devices to be of practical application. To decrease the turn-on time value of a deep-red light-emitting electrochemical cells (DR-LECs), two novel approaches based on molecularly engineered ruthenium phenanthroimidazole complexes were introduced. First, we found that with the incorporation of ionic methylpyridinium group to phenanthroimidazole ligand, the turn-on time of the DR-LECs device was dramatically reduced, from 79 to 27 s. By complexation of ruthenium emitter with Ag+, the turn-on time was improved by 85%, and the EQE of DR-device was increased from 0.62 to 0.71%. These results open a new avenue in decreasing the turn-on time without adding ionic electrolytes, leading to an efficient LEC.

Synthesis, Study, and Application of Pd(II) Hydrazone Complexes as the Emissive Components of Single-Layer Light-Emitting Electrochemical Cells.

For the first time, square planar Pd(II) complexes of hydrazone ligands have been investigated as the emissive components of light-emitting electrochemical cells (LECs). The neutral transition metal complex, [Pd(L1)2]·2CH3OH (1), (HL1 = (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinhydrazide), was prepared and structurally characterized. Complex 1 displays quasireversible redox properties and is emissive at room temperature in solution with a λmax of 590 nm. As a result, it was subsequently employed as the emissive material of a single-layer LEC with configuration FTO/1/Ga/In, where studies reveal that it has a yellow color with CIE(x, y) = (0.33, 0.55), a luminance of 134 cd cm-2, and a turn-on voltage of 3.5 V. Protonation of the pendant pyridine nitrogen atoms of L1 afforded a second ionic complex [Pd(L1H)2](ClO4)2 (2) which is also emissive at room temperature with a λmax of 611 nm, resulting in an orange LEC with CIE(x, y) = (0.43, 0.53). The presence of mobile anions and cations in the second inorganic transition metal complex resulted in more efficient charge injection and transport which significantly improved the luminance and turn-on voltage of the device to 188.6 cd cm-2 and 3 V, respectively. This study establishes Pd(II) hydrazone complexes as a new class of materials whose emissive properties can be chemically tuned and provides proof-of-concept for their use in LECs, opening up exciting new avenues for potential applications in the field of solid state lighting.

Two in One: A Dinuclear Ru(II) Complex for Deep-Red Light-Emitting Electrochemical Cells and as an Electrochemiluminescence Probe for Organophosphorus Pesticides.

The emissive properties of two Ru(II) complexes, [Ru(dmbipy)2L1][PF6]2 (1) and [Ru2(dmbipy)4L2][PF6]4 (2), (where L1 and L2 are π-extended phenanthroline-based ligands and dmbipy = 4,4'-dimethyl-2,2'-bipyridine) have been explored for dual applications, namely, deep-red light-emitting electrochemical cells (LECs) and electrochemiluminescence (ECL) sensors for the detection of organophosphorus pesticides (OPs) that include chlorpyrifos (CPS). A simple single-layer deep-red LEC device comprising 2 is reported that outperforms both its mononuclear derivative 1 and all previously reported dinuclear LECs, with a maximum brightness of 524 cd/m2, an external quantum efficiency of 0.62%, and a turn-on voltage of 3.2 V. Optoelectronic studies reveal that the ECL response of 2 is improved when compared to its mononuclear counterpart 1 and benchmark [Ru(bipy)3]2+ (3). Modified glassy carbon electrodes coated with 2 are highly sensitive deep-red ECL sensors that facilitate the detection of CPS directly from river water and fruit samples without any complex pretreatment steps, operating over a broad logarithmic concentration range, with a low detection limit.

Polypyridyl ligands as a versatile platform for solid-state light-emitting devices.

The replacement of inorganic semiconductors with molecule-based compounds for applications in current-to-light conversion has led to a significant increase in interdisciplinary collaborations worldwide, affording new improved organic-light emitting diodes (OLEDs) ripe for commercial applications, as well as light-emitting electrochemical cells (LECs) that have recently started to head to the market. This review highlights the role that transition metal coordination complexes (TMCs) have played in advancing the field of molecular electronics, from early conception to the advanced development of several polypyridyl complexes currently pursued for both OLED and LEC concepts. In this context, the design and synthesis of Ir(iii), Pt(ii), Cu(i) and Ag(i) complexes as the emissive components of OLEDs and LECs are thoughtfully presented. We discuss how molecular design is pivotal for fine-tuning color and optimizing power efficiencies, highlighting the key roles of the metal, cyclometalate, and ancillary polypyridyl ligands. We provide insight into the strategies exploited for the development of new, improved emitters and their fabrication into OLEDs/LECs with high external quantum efficiencies and stabilities. In addition, we have surveyed the remarkable photophysical properties of third generation TMCs capable of undergoing thermally activated delayed fluorescence (TADF). Since previous reviews of TADF materials are strongly biased towards organic-based systems, this overview compliments other synopses of light emitting TADF materials. Finally, we shed light onto the conceptual challenges that still need to be overcome to advance the rational design of TMC-based TADF emitters with tunable ligands and the subsequent fabrication of OLEDs/LECs, which are tailor-made for each specific application.

Influence of Ancillary Ligands in Dye-Sensitized Solar Cells.

Dye-sensitized solar cells (DSSCs) have motivated many researchers to develop various sensitizers with tailored properties involving anchoring and ancillary ligands. Ancillary ligands carry favorable light-harvesting abilities and are therefore crucial in determining the overall power conversion efficiencies. The use of ancillary ligands having aliphatic chains and/or π-extended aromatic units decreases charge recombination and permits the collection of a large fraction of sunlight. This review aims to provide insight into the relationship between ancillary ligand structure and DSSC properties, which can further guide the function-oriented design and synthesis of different sensitizers for DSSCs. This review outlines how the new and rapidly expanding class of chelating ancillary ligands bearing 2,2'-bipyridyl, 1,10-phenanthroline, carbene, dipyridylamine, pyridyl-benzimidazole, pyridyl-azolate, and other aromatic ligands provides a conduit for potentially enhancing the performance and stability of DSSCs. Finally, these classes of Ru polypyridyl complexes have gained increasing interest for feasible large-scale commercialization of DSSCs due to their more favorable light-harvesting abilities and long-term thermal and chemical stabilities compared with other conventional sensitizers. Therefore, the main idea is to inspire readers to explore new avenues in the design of new sensitizers for DSSCs based on different ancillary ligands.

Saddle-shaped porphyrins for dye-sensitized solar cells: new insight into the relationship between nonplanarity and photovoltaic properties.

We report on the theoretical and experimental studies of the new dye-sensitized solar cells functionalized with 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin zinc(II) complexes bearing 2- and 8-bromo substituents at the ß positions. In agreement with the results of TD-DFT calculations, the absorption maxima of di- and octa-brominated Zn(II) complexes, ZnTCPPBr2 and ZnTCPPBr8, exhibited large red-shift compared to that of the non-brominated free base porphyrin (H2TCPP). Furthermore, DFT calculations showed that the higher stabilization of the LUMO levels relative to the HOMO ones makes the HOMO-LUMO gap of the brominated Zn-porphyrins models smaller compared to that of the nonbrominated counterparts, which explains the red shifts of the Soret and Q bands of the brominated compounds. Solar cells containing the new saddle-shaped Zn(II) porphyrins were subjected to analysis in a photovoltaic calibration laboratory to determine their solar to electric energy conversion. In this regard, we found that the overall conversion efficiency of ZnTCPPBr8 adsorbed on TiO2 nanocrystalline films was 5 times as large as that of ZnTCPPBr2 adsorbed on the same films. The effect of the increasing number of Br groups on the photovoltaic performance of the complexes was compared to the results of computational methods using ab initio DFT molecular dynamics simulations and quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer (IET) in TCPPBrx/TiO2-anatase nanostructures. Better IET in ZnTCPPBr8 compared to ZnTCPPBr2, and in H2TCPP was evaluated from interfacial electron transfer (IET) simulations. The IET results indicate that electron injection in ZnTCPPBr8-TiO2 (τ = 25 fs) can be up to 5 orders of magnitude faster than ZnTCPPBr2-TiO2 (τ = 125 fs). Both experimental and theoretical results demonstrate that the increase of the number of bromo-substituents at the ß-pyrrole positions of the porphyrin macrocycle created a new class of porphyrin-based DSSC, which exhibits a remarkable increase in the photovoltaic performance compared to non-brominated porphyrins.

Enhancement of electroluminescence in zirconium poly carboxylic acid-based light emitting diodes by bathophenanthroline ligand.

The reactions of a zirconium salt with 1,2,4,5-benzenetetracarboxylate (btec), bathophenanthroline (Bphen) and thiocyanate ions were synthesized and studied by changing the mole ratio, the order of reactant and their pH. It is found that the coordination mode of btec acid depends on the control of reaction conditions. Monodentate, bidentate and bridging modes were investigated by FT-IR spectroscopy. The structures of Zr(btec) and Zr(btec)(Bphen) complexes were also characterized by UV-Vis, CHN, ICP-AES, (1)H NMR and cyclic voltammetry. The role of Bphen ligand in the photopysical properties of Zr(btec)(Bphen) complexes was investigated by DFT calculation. The photoluminescence (PL) emission of nine Zr(btec) complexes that have two peaks, a sharp and intense band for the first peak from 320 to 430 nm in comparison to the second peak with a less intensity and broadened in the regions of 650-780 nm. PL spectra of twelve Zr(btec)(Bphen) complexes also showed bands at 450, 550, 625 nm. LED devices with Zr complex as emitter layer and the structure ITO/PEDOT:PSS/PVK:PBD/zirconium complex/Al emitted a broad band centered at 550 and 650 originating from the Zr complexes. The EL spectra of Zr(btec) and Zr(btec)(Bphen) complexes indicated a long red shift rather than PVK:PBD blend. We believe that the electroplex occurring at PVK-Zr complexes interface is responsible for the green-red emission in the EL of the device. These observations suggest an important role for the Bphen ligand to improve EL performance.

Shedding light on the environmental impact of the decomposition of perovskite solar cell.

Perovskite materials, as the heart of perovskite solar cells (PSC), attracted great interest in the photovoltaic community since the efficiency of PSC dramatically increased to over 25% in a short period. However, the presence of Pb metal in the perovskite crystalline limits the progress of this new generation of solar cells from environmental aspects. Here, we have systematically investigated the impact of the decomposition of perovskite material on the special plant, named Coleus. The influence of the decomposition of a perovskite solar cell (p-PbI2) has a three-fold lower destruction than commercial PbI2 (s-PbI2) in the same condition. The p-PbI2 made destroying the roots and leafs slower and smoother than s-PbI2, which the amount of water absorption with the plant's root from p-PbI2 is two-fold lower than s-PbI2. The atomic absorption spectroscopy (AAS) indicated that the amount of Pb in the first week is about 3.2 and 2.1 ppm for s-PbI2, and p-PbI2, respectively, which in following for two next weeks reached to about relatively close together and finally in the last week decreased to 1.8 ppm for s-PbI2 and increased to 2.4 ppm for p-PbI2. This paper opens new avenues and challenges about the actual scenario on the impact of perovskite materials in PSCs on the plant and live metabolisms.

Mechanistic insights into the key role of methylammonium iodide in the stability of perovskite materials.

The possible mechanisms damaging perovskite solar cells have attracted considerable attention in the photovoltaic community. This study answers specifically open problems regarding the critical role of methylammonium iodide (MAI) in investigations as well as stabilizing the perovskite cells. Surprisingly, we found that when the molar ratio between PbI2 : MAI precursor solution increased from 1 : 5 to 1 : 25, the stability of perovskite cells dramatically increased over time. The stability of perovskite in the air without any masking in the average stoichiometry was about five days, while when the amount of MAI precursor solution increased to 5, the perovskite film was unchanged for about 13 days; eventually, when the value of MAI precursor solution enhanced to 25, the perovskite film stayed intact for 20 days. The outstanding XRD results indicated that the intensity of perovskite's Miler indices increased significantly after 24 h, and the MAI's Miler indices decreased, which means that the amount of MAI was consumed to renew the perovskite crystal structure. In particular, the results suggested that the charging of MAI using the excess molar ratio of MAI reconstructs the perovskite material and stabilizes the crystal structure over time. Therefore, it is crucial that the main preparation procedure of perovskite material is optimized to 1 unit of Pb and 25 units of MAI in a two-step procedure in the literature.

New molecularly engineered binuclear ruthenium(II) complexes for highly efficient near-infrared light-emitting electrochemical cells (NIR-LECs).

From the practical point of view, the stability, response time and efficiency of near-infrared light-emitting electrochemical cells (NIR-LECs) are key factors. By using the high potential of chemical modification potential of the phenanthroimidazole ligand, three new binuclear ruthenium(II) complexes with an alkyl spacer as the NIR-emitter were designed and synthesized. NIR-LECs based on these complexes exhibit near-infrared emission at the maximum wavelength of up to 705 nm and with an EQE of up to 0.72% at 4.0 V, which are among the highest values for NIR-LECs based on cationic binuclear ruthenium(II) complexes reported so far. The lifetimes of NIR-LECs based on binuclear complexes were increased about 1.5-to-4-fold with respect to the ones based on mononuclear complexes. Furthermore, a significant decrease in the turn-on time of NIR-LECs by chemical tethering of a new ionic methylpyridinium moiety from 6.3 to 1.4 minutes was observed. It seems that this combinational modification approach can open a new avenue for practical applications.

Molecularly engineered hole-transport material for low-cost perovskite solar cells.

Triphenylamine-N-phenyl-4-(phenyldiazenyl)aniline (TPA-AZO) is synthesized via a facile CuI-catalyzed reaction and used as a hole transport material (HTM) in perovskite solar cells (PSCs), as an alternative to the expensive spiro-type molecular materials, including commercial 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Experimental and computational investigations reveal that the highest occupied molecular orbital (HOMO) level of TPA-AZO is deeper than that of spiro-OMeTAD, and optimally matches with the conduction band of the perovskite light absorber. The use of TPA-AZO as a HTM results in PSC prototypes with a power conversion efficiency (PCE) approaching that of the spiro-OMeTAD-based reference device (17.86% vs. 19.07%). Moreover, the use of inexpensive starting reagents for the synthesis of TPA-AZO makes the latter a new affordable HTM for PSCs. In particular, the cost of 1 g of TPA-AZO ($22.76) is significantly lower compared to that of spiro-OMeTAD ($170-475). Overall, TPA-AZO-based HTMs are promising candidates for the implementation of viable PSCs in large-scale production.

Molecularly engineered electroplex emission for an efficient near-infrared light-emitting electrochemical cell (NIR-LEC).

Electroplex emission is rarely seen in ruthenium polypyridyl complexes, and there have been no reports from light-emitting electrochemical cells (LECs) to date. Here, for the first time, near-infrared (NIR) emission via the electroplex mechanism in a LEC based on a new blend of ruthenium polypyridyl complexes is described. The key factor in the design of the new complexes is the 0.4 V decrease in the oxidation half-potential of Ru(ii)/Ru(iii) in [Ru(DPCO)(bpy)2]ClO4 (DPCO = diphenylcarbazone, bpy = 2,2 bipyridine), which is about one-third of the value for benchmark [Ru(bpy)3](ClO4)2, as well as the long lifetime of excited states of 350-450 ns. The LEC based on the new blend with a narrow band gap (≈1.0 eV) of a Ru(DPCO) complex and Ru(bpy)3 2+ can produce an electroluminescence spectrum centred at about 700 nm, which extends to the NIR region with a high external quantum efficiency (EQE) of 0.93% at a very low turn-on voltage of 2.6 V. In particular, the very simple LEC structure was constructed from indium tin oxide (anode)/Ru(DPCO):Ru(bpy)3 2+/Ga:In (cathode), avoiding any polymer or transporting materials, as well as replacing Al or Au by a molten alloy cathode. This system has promising applications in the production of LECs via microcontact or inkjet printing.

A near infrared light emitting electrochemical cell with a 2.3 V turn-on voltage.

We report on an organic electroluminescent device with simplified geometry and emission in the red to near infrared (NIR) spectral region which, has the lowest turn-on voltage value, 2.3 V, among light emitting electrochemical cells (LEECs). We have synthesized and characterized three novel ruthenium π-extended phenanthroimidazoles which differ on their N^N ligands. The use of dimethyl electron donating groups along with the π-extended phenanthroimidazole moiety promotes ambipolar transport thereby avoiding the use of additional charge transport layers. Furthermore, a facile cathode deposition method based on transfer of a molten alloy (Ga:In) on top of the active layer is deployed, thus avoiding high vacuum thermal deposition which adds versatile assets to our approach. We combine ambipolar charge transport organic complex design and a simple ambient cathode deposition to achieve a potentially cost effective red to NIR emitting device with outstanding performance, opening new avenues towards the development of simplified light emitting sources through device optimization.

Ultrafast interfacial charge transfer from the LUMO+1 in ruthenium(ii) polypyridyl quinoxaline-sensitized solar cells.

This paper describes the implementation of robust and modular sensitizers containing aromatic-amphiphilic ligands to provide new insights into the relationship between the molecular structure and electron injection process governing the efficiency of dye-sensitized solar cells (DSSCs). The significance of this work lies in the combination of favorable experimental and theoretical results in a new class of Ru(ii) polypyridyl complexes with the molecular formula of [Ru(E101)(Dicnq)x(Y)] which is named M101-M104 when X = 1 and Y = bpy, X = 1 and Y = phen, X = 2, and X = 1 and Y = 2 NCS, respectively. E101 and Dicnq ligands are 1,10-phenanthroline-5,6 heptan ammin and 6,7-dicyanodipyrido[2,2-d:2',3'-f]quinoxaline, respectively. The good agreement between the experimental and the time-dependent density functional theory (TDDFT)-calculated absorption spectra of the M101-104 sensitizers allowed us to provide a detailed assignment of the main spectral features of the investigated dyes. M102 which contained phen as an ancillary ligand had the best photovoltaic performance which can be attributed to the higher light harvesting of M102 in the visible light region. A DSSC based on complex M102 without the E101 ligand did not show any observable power conversion efficiency (PCE), indicating the importance of the amphiphilic ligand, E101. Transient absorption studies indicated that the ratio of kreg/krec (krec = the rate constant of the recombination of the dye and kreg = the rate constant of regeneration in the presence of the electrolyte) for M101-104 is 1.1, 2.9, 1.3, and 1.2, clearly confirming a weak competition between dye regeneration and recombination. Therefore, because this ratio for M101, 103, and 104 is small, kreg ≈ krec, the operation of the device has been limited by back electron transports, subsequently enhancing the recombination process. However, the rate of recombination is relatively normal for an efficient DSSC, while the rate of regeneration is very low. Subsequently, the PCE will be poor, confirming the role of aliphatic chains in reducing the recombination process. To obtain a deeper insight into the charge transfer process in the investigated devices, ab initio DFT molecular dynamics simulations and quantum dynamics of electronic relaxation were carried out, clearly showing that the interfacial electron transfer (IET) time scale particularly depends on the type of ancillary ligand. The IET results substantially proved that M102 has the fast lifetime of 2.3 ps and 90 fs for the LUMO and LUMO+1, respectively, indicating the experimentally higher PCE of M102 compared to the other three investigated sensitizers.

On how ancillary ligand substitution affects the charge carrier dynamics in dye-sensitized solar cells.

With respect to N3, a champion sensitizer in dye-sensitized solar cells (DSSCs), S3 which contained a phenTz (1,10-phenanthroline 5-tetrazole) ancillary ligand showed outstanding improvements in molar extinction coefficient (ε) from 10 681.8 to 12 954.5 M cm-1 as well as 0.92% and 0.9% increases in power conversion efficiency (PCE) and incident photon-to-electron conversion efficiency (IPCE), reaching 8.46% and 76.5%, respectively. To find the origin of the high performance of the DSSC based on a phenTz ancillary ligand, transient absorption spectroscopy (TA) was carried out and indicated that the rate of the regeneration reaction is about 100 times faster than the rate of recombination with the dye which is very exciting and surely a good reason to promote the phenTz ligand as a promising ancillary ligand in DSSCs.

Low-Turn-On-Voltage, High-Brightness, and Deep-Red Light-Emitting Electrochemical Cell Based on a New Blend of [Ru(bpy)3]2+ and Zn-Diphenylcarbazone.

Deep red light-emitting electrochemical cells were prepared based on a blend of [Ru(bpy)3]2+, a cationic complex, and a neutral Zn(II)-complex based on diphenylcarbazone ligands, named Zn(DPCO). The crystal structure of the Zn(DPCO)2 (bpy)] molecule revealed that the DPCO ligand has been deprotonated to form DPCO- and coordinated to the Zn center metal through the C=O and N=N moieties of DPCO. From the cyclic voltammetry results and controlled potential coulometry data of the diphenylcarbazide (DPC) ligand, it is possible to establish that DPC is oxidized in an irreversible process at +0.77 V, giving DPCO and later oxidized at a higher potential (+1.32 V) to produce diphenylcarbadiazone (DPCDO). A detailed assignment of UV-vis spectra futures to determine the origin of ground- and excited-state transitions was achieved by time-dependent density functional theory calculations, which showed good agreement with the experimental results. Using a simple device architecture, we obtained deep red electroluminescence (EL) with high brightness (740 cd m-2) and luminous efficiency of 0.39 cd/A at a low turn-on voltage of 2.5 V. The favorable configuration of the cell consists of only a blend of complexes of indium tin oxide as the anode electrode and molten alloy cathode (Ga/In) without any polymer as the transporting layer. The comparison between [Ru(bpy)3]2+ and [Ru(bpy)3]2+/Zn(DPCO) demonstrates a red shift in the EL wavelength from 625 to 700 nm in the presence of Zn(DPCO), revealing the importance of using blends for future systems.

Efficient near infrared light emitting electrochemical cell (NIR-LEEC) based on new binuclear ruthenium phenanthroimidazole exhibiting desired charge carrier dynamics.

Near-infrared light-emitting electrochemical cell (NIR-LEEC) has emerged as a new and promising lighting sourcewhich could serve as low-cost alternatives in NIR light-emitting sources which are typically expensive. LECs were also shown advantages such as light weight, simplicity and low operation voltages. However, only a few examples of NIR-LEEC are reported in which external quantum efficiency(EQE) of devices limited to 0.1%. Here, we report, efficient NIR-LEEC based of two novel binuclear ruthenium phenanthroimidzole complex which differ by employing the type of ancillary ligand including 2, 2'bipyridine (bpy) (B1) and 4, 4' dimethyl bpy (B2) that realize maximum EQE of 0.14 and 0.68% and extremely long excited state lifetimes of 220 and 374 ns for thin film were estimated, respectively, indicating that influences of substitution on ancillary ligand. Moreover, this substitution dramatically influences other electroluminescence metrics including decreasing turn on voltage from 4.5 to 3.1 V, increasing maximum luminance (Lmax) from 193to 742 cd.m-2 and increasing lifetime from 539 to 1104 second, which are the best value among the binuclear ruthenium polypyridyl complexes to date.