Global AM Research Articles

Effects of donors of bodipy dyes on the performance of dye-sensitized solar cells

A new series of donor-acceptor-π-linker-acceptor (D–A–π–A) featured organic dyes containing Bodipy derivative as the auxiliary acceptor, furan unit as the π conjugated spacer, and 2-cyanoacrylic acid as the anchor group were synthesized and applied in dye-sensitized solar cells (DSSCs). The incorporated electron-withdrawing unit of Bodipy enhances light harvesting by decreasing the molecular energy gap and red-shifting absorption spectra. For comparison, three different arylamine chromophores namely 3-methoxy-9H-carbazole (CBZ-B), triphenylamine (TPA-B) and phenoxazine (POZ-B) were separately appended onto the 6-position of Bodipy unit to study the effect of the electron donating groups on device performance. The UV–vis absorption spectra, electrochemical properties, density functional theory calculation, photovoltaic properties and electrochemical impedance measurements of DSSCs with these three dyes were systematically investigated. The Bodipy dyes have broad absorption spectra covering the range of 250–700 nm with the highest molar extinction coefficient up to >55 000 M−1 cm−1. The molecular energy level tuning can be conveniently accomplished by alternating the donor moiety. The DSSCs based on TPA-B showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 70%, a short-circuit photocurrent density (Jsc) of 13.95 mA cm−2, an open-circuit photovoltage (Voc) of 557 mV, and a fill factor (ff) of 0.61, corresponding to an overall conversion efficiency of 4.76% under standard global AM 1.5G solar light conditions. Our research demonstrates that Bodipy based D–A–π–A molecular architecture is a highly promising class for the improvement of the performance of DSSCs in the future.

Dithiafulvene-based organic sensitizers using pyridine as the acceptor for dye-sensitized solar cells

Three dithiafulvene-based metal-free organic sensitizers all using pyridine as the acceptor but with different π-bridges of phenyl (DTF-Py1), thienyl (DTF-Py2) and phenyl-thienyl (DTF-Py3) have been designed, synthesized and used as photosensitizers for dye-sensitized solar cells (DSCs). Introducing thienyl unit into the π-bridge, as well as extension of the π-bridge can dramatically improve their light harvesting ability and suppress the electron recombination, thus uplifting the performance of DSCs. The overall power conversion efficiency of DSC based on DTF-Py3 shows the highest efficiency of 2.61% with a short-circuit photocurrent density of 7.99 mA cm−2, an open-circuit photovoltage of 630 mV, and a fill factor of 0.52, under standard global AM 1.5 solar light condition. More importantly, the long-term stability of the DTF-Py3 based DSCs under 500 h light-soaking has been demonstrated.

Numerical modeling of a CdS/CdTe photovoltaic cell based on ZnTe BSF layer with optimum thickness of absorber layer

High efficiency ultrathin CdTe film is an excellent candidate for reliable, efficient, stable and low cost solar cells. In this paper, a high efficiency CdS/CdTe solar cell has been studied by using ADEPT 1D simulation tool. The proposed device has been simulated with a reduced CdTe absorber layer thickness and a ZnTe layer as back surface field (BSF) which substantiates sensible energy conversion efficiency. The investigation into the simulation results showed that the conversion efficiency with BSF layer and 1 μm thick CdTe absorber is 8.24% more as compared to the conventional CdTe cells (without BSF layer). Reduction of minority carrier recombination loss due to the insertion of BSF layer at the back contact in ultra-thin CdS/CdTe cells has also been investigated. The results depict that CdTe cell with BSF layer is responsible for increasing the quantum efficiency. However, the proposed structure of ZnO/CdS/CdTe/ZnTe demonstrates the highest efficiency of 24.66% (Voc = 946.51 mV, Jsc = 34.40 mA/cm2 and FF = 75.72%) under global AM1.5G illumination spectra.

New banana shaped A–D–π–D–A type organic dyes containing two anchoring groups for high performance dye-sensitized solar cells

Two new bent A–D–π–D–A type organic dyes (MA-1 and MA-2) consisting of carbazole and phenothiazine moieties as electron donors with 2,1,3-benzothiadiazole as a π-linker with two end-anchoring groups are designed, synthesized and tested in DSSCs. The photophysical and electrochemical properties of the dyes are investigated in detail. Incorporation of phenothiazine unit in MA-2 resulted in high HOMO level (0.62 V vs. NHE), with a red shift in absorption maxima and broadening of the absorption spectrum. Under standard global AM 1.5 solar conditions, the MA-2 sensitized solar cells exhibited a short circuit photocurrent density of 13.1 mA cm−2, an open-circuit voltage of 0.73 V, a fill factor of 0.72, corresponding to an overall conversion efficiency of 6.87%. Such design and development of molecular dyes are useful for improving the overall efficiency of DSSCs.

Novel organic dye sensitizers containing fluorenyl and biphenyl moieties for solar cells

Three novel triarylamine dyes (AFL1–AFL3) containing fluorenyl and the biphenyl moieties have been designed and synthesized for application in dye-sensitized solar cells. The light-harvesting capabilities and photovoltaic performance of these dyes were investigated systematically through comparison of different π-bridges. The dye with a furan linker exhibited a higher open-circuit voltage (VOC) and monochromatic incident photon-to-current conversion efficiency (IPCE) compared to thiophene and benzene linker. Thus, AFL3 containing a furan linker exhibited the maximum overall conversion efficiency of 5.81% (VOC=760mV,JSC=11.36mAcm−2 and ff=0.68) under standard global AM 1.5 G solar condition.

Design of Far-Red Sensitizing Squaraine Dyes Aiming Towards the Fine Tuning of Dye Molecular Structure.

Model squaraine dyes having sharp and narrow absorptions mainly in the far-red wavelength region has been logically designed, synthesized and used for their application as sensitizer in the dyesensitized solar cells (DSSC). In order to have fine control on energetics, dyes having same mother core and alkyl chain length varying only in molecular symmetry and position of substituent were designed. It has been found that even keeping all other structural factor constant, only positional variation of substituent leads to not only in the variation of energetics by 0.1 eV but affects the photovoltaic characteristics also. Optimum concentration of dye de-aggregating agent was found to be 100 times with respect to the sensitizing dye concentration. Amongst dyes utilized in this work best performance was obtained for unsymmetrical dye SQ-40 giving a photoconversion efficiency of 4.01% under simulated solar irradiation at global AM 1.5.

Naphtho[2,3-c][1,2,5]thiadiazole and 2H-Naphtho[2,3-d][1,2,3]triazole-Containing D-A-π-A Conjugated Organic Dyes for Dye-Sensitized Solar Cells.

Dipolar dyes comprising an arylamine as the electron donor, a cyanoacrylic acid as electron acceptor, and an electron deficient naphtho[2,3-c][1,2,5]thiadiazole (NTD) or naphtho[2,3-d][1,2,3]triazole (NTz) entity in the conjugated spacer, were developed and used as the sensitizers in dye-sensitized solar cells (DSSCs). The introduction of the NTD unit into the molecular frame distinctly narrows the HOMO/LUMO gap with electronic absorption extending to >650 nm. However, significant charge trapping and dye aggregation were found in these dyes. Under standard global AM 1.5 G illumination, the best cell photovoltaic performance achieved 6.37 and 7.53% (∼94% relative to N719-based standard cell) without and with chenodeoxycholic acid (CDCA) coadsorbent, respectively. Without CDCA, the NTz dyes have higher power conversion efficiency (7.23%) than NTD dyes due to less charge trapping, dye aggregation, and better dark current suppression.

Effect of electron-withdrawing groups in conjugated bridges: molecular engineering of organic sensitizers for dye-sensitized solar cells

Four organic sensitizers containing quinoxaline or benzoxadiazole as an auxiliary electron acceptor in conjugated bridge were synthesized and utilized for dye-sensitized solar cells (DSSCs). It was found that the incorporation of different electron-withdrawing moieties can affect the absorption spectra, electronic properties, the interfacial interactions and then the overall conversion efficiencies significantly. Therefore, the appropriate selection of the auxiliary acceptor was important to optimize the photovoltaic performance of solar cells. Among these sensitizers, LI-44 based solar cell showed the best photovoltaic performance: a shortcircuit photocurrent density (J sc) of 13.90 mA/cm2, an open-circuit photovoltage (V oc) of 0.66 V, and a fill factor (FF) of 0.66, corresponding to an overall conversion efficiency of 6.10% under standard global AM 1.5 solar light conditions.

Near-infrared unsymmetrical blue and green squaraine sensitizers.

Two novel panchromatic asymmetrical squaraine sensitizers (SPSQ1 and SPSQ2) have been synthesized, characterized and effectively used for TiO2-based dye sensitized solar cells. In a solution, both dyes display a highly intense near-IR absorption (SPSQ1; 651 nm and SPSQ2; 692 nm), the red shifted absorption of SPSQ2 was attributed to the incorporation of the auxiliary acceptor dicyanovinyl unit on the squaraine moiety. Interestingly, the dicyanovinyl unit lowered the LUMO level of SPSQ2, which decreased the band gap and red shifted the absorption when compared to SPSQ1. These dyes possess suitable HOMO and LUMO levels to work as efficient sensitizers in DSSCs. The experimental trends in their optical and electrochemical properties are well matched with the theoretical calculations modeled by TDDFT. The blue and green color of the devices showed their complementary absorption and harvest a greater number of photons from solar flux. Under standard global AM 1.5 G solar conditions, the DSSC based on SPSQ2 exhibited a high power conversion efficiency of 3.1% with a high short circuit current density (JSC) attributed to the broadening of the IPCE spectra in the UV-vis and near-IR regions when compared to SPSQ1 (2.5%).

Donor-π-donor type hole transporting materials: marked π-bridge effects on optoelectronic properties, solid-state structure, and perovskite solar cell efficiency.

Donor-π-bridge-donor type oligomers (D-π-D) have been studied intensively as active materials for organic optoelectronic devices. In this study, we introduce three new D-π-D type organic semiconductors incorporating thiophene or thienothiophene with two electron-rich TPA units, which can be easily synthesized from commercially available materials. A thorough comparison of their optoelectronic and structural properties was conducted, revealing the strong influence of the extent of longitudinal π-bridge conjugation on both the solid structure of the organic semiconductive materials and their photovoltaic performance when applied as hole transporting materials (HTM) in perovskite solar cells. Single-crystal measurements and time-resolved photoluminescence (TRPL) studies indicate that these coplanar donor-π-donor type HTMs could be promising alternatives to state-of-the-art spiro-OMeTAD, due to the multiple intermolecular short contacts as charge transporting channels and efficient charge extraction properties from the perovskite layer. The optimized devices with PEH-9 exhibited an impressive PCE of 16.9% under standard global AM 1.5 illumination with minimized hysteretic behaviour, which is comparable to that of devices using spiro-OMeTAD under similar conditions. Ambient stability after 400 h revealed that 93% of the energy conversion efficiency was retained for PEH-9, indicating that the devices had good long-term stability.

Indole-based organic dyes with different electron donors for dye-sensitized solar cells

Three novel organic dyes WY1, WY2 and WY3 with the same π-conjunction linker and acceptor but different donor units were synthesized and characterized to investigate the effects of different electron donor units on their photophysical, electrochemical and photovoltaic properties. Density functional theory calculations were carried out to study the ground state geometry structures and electronic structures of the three dyes. Under standard global AM 1.5 solar condition, the solar cells based on WY1, WY2 and WY3 show the overall power conversion efficiencies as 2.15%, 3.30% and 2.09%, respectively. All the investigation results reveal that different electron donors in organic dyes could cause significant differences in photovoltaic performances and organic dye WY2 with N-hexylphenothiazine as electron donor could show the best performance among the three dyes.

Rational Molecular Engineering of Indoline-Based D-A-π-A Organic Sensitizers for Long-Wavelength-Responsive Dye-Sensitized Solar Cells.

Indoline-based D-A-π-A organic sensitizers are promising candidates for highly efficient and long-term stable dye-sensitized solar cells (DSSCs). In order to further broaden the spectral response of the known indoline dye WS-2, we rationally engineer the molecular structure through enhancing the electron donor and extending the π-bridge, resulting in two novel indoline-based D-A-π-A organic sensitizers WS-92 and WS-95. By replacing the 4-methylphenyl group on the indoline donor of WS-2 with a more electron-rich carbazole unit, the intramolecular charge transfer (ICT) absorption band of dye WS-92 is slightly red-shifted from 550 nm (WS-2) to 554 nm (WS-92). In comparison, the incorporation of a larger π-bridge of cyclopentadithiophene (CPDT) unit in dye WS-95 not only greatly bathochromatically tunes the absorption band to 574 nm but also largely enhances the molar extinction coefficients (ε), thus dramatically improving the light-harvesting capability. Under the standard global AM 1.5 solar light condition, the photovoltaic performances of both organic dyes have been evaluated in DSSCs on the basis of the iodide/triiodide electrolyte without any coadsorbent or cosensitizer. The DSSCs based on WS-95 display better device performance with power conversion efficiency (η) of 7.69%. The additional coadsorbent in the dye bath of WS-95 does not improve the photovoltaic performance, indicative of its negligible dye aggregation, which can be rationalized by the grafted dioctyl chains on the CPDT unit. The cosensitization of WS-95 with a short absorption wavelength dye S2 enhances the IPCE and improves the η to 9.18%. Our results indicate that extending the π-spacer is more rational than enhancing the electron donor in terms of broadening the spectral response of indoline-based D-A-π-A organic sensitizers.

Comparative studies of organic dyes with a quinazoline or quinoline chromophore as π-conjugated bridges for dye-sensitized solar cells

A new series of organic D–π–A dyes bearing either quinazoline or quinoline as the conjugated bridges in the chromophore with a diphenylamine moiety as the electron donor and a cyanoacetic acid unit as the electron acceptor, have been designed and synthesized for photoconversion in dye sensitized solar cells (DSSCs). The absorption spectra, density functional theory calculations, electrochemical and photovoltaic properties of these dyes are systematically investigated. Among the four dyes the sensitized solar cell based upon the quinoline dye bearing butoxy groups gave a short circuit photocurrent density of 7.04 mA cm−2, an open circuit voltage of 0.52 V, and a fill factor of 0.69, corresponding to an overall conversion efficiency of 2.51% using I−/I3− redox couple-based liquid electrolyte without 4-tert-butylpyridine additives under standard global AM 1.5 irradiation (100 mW cm−2). The photovoltaic performance of the dye with 4,4′-dibutoxy diphenylamine as the donor and quinoline unit as the π-bridge was higher than that of the other photosensitizers, which is mainly attributed to the higher molar extinction coefficient and broader absorption band. The experimental results demonstrate that rational molecular engineering is crucial for constructing highly efficient charge transfer sensitizers.

2,3-Dipentyldithieno[3,2-f:2',3'-h]quinoxaline-Based Organic Dyes for Efficient Dye-Sensitized Solar Cells: Effect of π-Bridges and Electron Donors on Solar Cell Performance.

Five novel metal-free organic dyes DQ1-5 containing a dipentyldithieno[3,2-f:2',3'-h]quinoxaline (DPQ) unit were synthesized and applied in dye-sensitized solar cells (DSSCs), where DPQ was employed as a π-spacer for the first time. Their photophysical, electrochemical, and theoretical calculations and photovoltaic properties were systematically investigated. All the five dyes show broad photoresponse. Especially the absorption edges of DQ3-5 extend to 800 nm on the TiO2 films. The inserted electron-rich unit 3,4-ethylenedioxythiophene or electron-withdrawing group benzothiadiazole (BTD) in DPQ-based dyes can greatly influence the optoelectronic properties of the dyes. In addition, the different electron donors also significantly affect the performance of the DSSCs. Under standard global AM 1.5 solar light conditions, the DQ5 sensitized solar cell obtained a power conversion efficiency of 7.12%. The result indicates that the rigid DPQ-based organic dye is a promising candidate for efficient DSSCs.

The Global AM Radio Conundrum:

AbstractDue to electronic radio frequency encroachment, AM radio signal quality is deteriorating. As a result, the U.S. FCC is offering unprecedented technical assistance. This exploratory study documents the disposition of media managers about the future of the AM band in North America and Europe, the recent FCC’s efforts and role of new digital technologies. Findings show that elite interviewees offered candid and surprising comments on the state of AM radio and the advent of digital delivery.

Synthesis, crystal structure and properties of one-dimensional Ni(II) coordination polymer

A new metal-organic coordination polymer {[Ni(L)(en)2]·2DMF}n (L: azobenzene-4,4′-dicarboxylate; en: ethylenediamine; DMF: N, N-dimethylformamide) (compound 1) has been synthesised under solvothermal condition. Compound 1 is characterised by single-crystal X-ray diffraction (XRD), infrared (IR) spectra, elemental analysis, powder XRDs and thermogravimetric analysis (TGA). The results show that compound 1 display blue fluorescence emission in the solid state at room temperature, which is attributed to π-π* intraligand electronic transition. This electronic transition indicates that compound 1 can be a sensitiser for dye-sensitised solar cells. Dye-sensitised solar cells with compound 1/N719 exhibit a short-circuit photocurrent density as high as 11.80 mA cm− 2, open-circuit photovoltage of 0.82 V, the fill factor of 0.65, and overall conversion efficiency of 6.28% under standard global AM1.5 solar irradiation conditions.

Molecular Engineering and Theoretical Investigation of Novel Metal-Free Organic Chromophores for Dye-Sensitized Solar Cells

In this work we report design and synthesis of three new metal free D-D–A–π–A type dyes (E1-3) with different acceptor/anchoring groups, as effective sensitizers for nanocrystalline titanium dioxide based dye sensitized solar cells. All the three dyes carry electron donating methoxy group as an auxiliary and indole as a principal donor, cyanovinylene as an auxiliary acceptor and thiophene as a π-spacer. Whereas, cyanoacetic acid, rhodanine-3-acetic acid and 4-aminobenzoic acid perform as acceptor/anchoring moieties, respectively in the dyes E1-3. Though the dye containing 4-aminobenzoic acid unit (E3) exhibits comparatively lower λmax, it shows the highest power conversion efficiency arising from the higher electron life time and good light-harvesting capability. The DFT studies reveal a better charge separation between the HOMO and LUMO levels of E3, further substantiating the experimental results. Among the three dyes, E3 shows the best photovoltaic performance with short-circuit current density (Jsc) of 9.35mA cm−2, open-circuit voltage (Voc) of 620mV and fill factor (FF) of 0.71, corresponding to an overall conversion efficiency of 4.12% under standard global AM 1.5G.

Enhanced performance of ruthenium dye-sensitized solar cell by employing an organic co-adsorbent of N , N ’-bis((pyridin-2-yl)(methyl) methylene)- o -phenylenediamine

Abstract A pyridine-anchor co-adsorbent of N , N ’-bis((pyridin-2-yl)(methyl) methylene)- o -phenylenediamine (named BPPI) is prepared and employed as co-adsorbent in dye-sensitized solar cells (DSSCs). The prepared co-adsorbent could overcome the deficiency of N719 absorption in the low wavelength region of visible spectrum, offset competitive visible light absorption of I 3 − , enhance the spectral responses of the co-adsorbed TiO 2 film in region from 300 nm to 750 nm, suppress charge recombination, prolong electron lifetime, and decrease the total resistance of DSSCs. The optimized cell device co-sensitized by BPPI/N719 dye gives a short circuit current density of 12.98 mA cm −2 , an open circuit voltage of 0.73 V, and a fill factor of 0.66 corresponding to an overall conversion efficiency of 6.22% under standard global AM 1.5 solar irradiation, which is much higher than that of device solely sensitized by N719 (5.29%) under the same conditions. Mechanistic investigations are carried out by various spectral and electrochemical characterizations.

Highly efficient and stable cyclometalated ruthenium(II) complexes as sensitizers for dye-sensitized solar cells

Four novel thiocyanate-free cyclometallted Ru(II) complexes, D-bisCF3, D-CF3, D-OMe, and D-DPA, with two 4,4′-dicarboxylic acid-2,2′-bipyridine together with a functionalized phenylpyridine ancillary ligand, have been designed and synthesized. The effect of different substituents (R=bisCF3, CF3, OMe, and DPA) on the ancillary C^N ligand on the photophysical properties and photovoltaic performance is investigated. Under standard global AM 1.5 solar conditions, the device based on D-CF3 sensitizer gives a higher conversion efficiency of 8.74% than those based on D-bisCF3, D-OMe, and D-DPA, which can be ascribed to its broad range of visible light absorption, appropriate localization of the frontier orbitals, weak hydrogen bonds between -CF3 and -OH groups at the TiO2 surface, moderate dye loading on TiO2, and high charge collection efficiency. Moreover, the D-bisCF3 and D-CF3 based DSSCs exhibit good stability under 100mWcm−2 light soaking at 60°C for 400h.

Facile synthesis of tungsten carbide nanorods and its application as counter electrode in dye sensitized solar cells

Tungsten carbide nanorods (WC-NRs) are synthesized by pseudomorphic transformation of chemically synthesized W3O8 nanorods using a high-temperature method. The WC-NRs was introduced into dye sensitized solar cell (DSSC) as counter electrode (CE) catalyst to replace the expensive platinum (Pt). The synthesized WC-NRs were characterized by field emission scanning electron microscopy (FESEM), BET surface area analysis and powder X-ray diffraction (PXRD) measurements. The electrochemical properties of WC-NRs counter electrode were studied using electrochemical impedance spectroscopy (EIS) techniques. The photovoltaic performance of the DSSC with WC-NRs counter electrode was evaluated under simulated standard global AM 1.5G sunlight (100mW/cm2). The solar to electrical energy conversion efficiency (η) of the WC-NRs with binder and binder free based DSSC was found to be 1.92% and 0.59% respectively. The cell performance can be attributed to the WC-NRs network, catalytic redox activity and 1-D efficient charge-transfer network. Such WC-NRs configuration as CE provides a potential feasibility for counter electrodes in DSSC applications.