Effect Of Π-bridge Research Articles

Effect of π-Bridge in D–π–A Architecture and Adsorption of Phenothiazine Dyes on TiO2 Nanocrystalline for Dye-Sensitized Solar Cells: A DFT Approach

In this work, the impact of extending [Formula: see text]-bridge and the adsorption of dyes on the nanocrystalline surface of TiO2 on photovoltaic parameters in dye-sensitized solar cells (DSSCs) has been explored. The dyes comprise phenothiazine (donor), along with benzene, furan, thiophene and selenophene ([Formula: see text]-spacers), and cyanoacrylic acid anchoring group (acceptor). The dye geometries, charge transference, and electronic characteristics were investigated using density functional theory (DFT). The impact of extended [Formula: see text]-bridge in conjugated systems was explored in dyes along with dyes adsorbed on TiO2 nanocrystalline surface (dye@TiO[Formula: see text]. For the architecture D–[Formula: see text]–A in this work, the dyes are effectively adsorbed on the TiO2 nanocrystalline surface. The energy gap between HOMO and LUMO (HLG), ionization potential (IP), reorganization energies ([Formula: see text], electron affinity (EA), photovoltaic parameters, adsorption energy (AE), and total density of state (TDOS) are simulated theoretically. Additionally, our investigation illustrates that the studied organic photosensitizer dyes may have improved photovoltaic characteristics and are suitable applicants for efficient charge transportation in organic electronic materials.

Theoretical analysis on D-π-A triphenylamine-based dyes for dye-sensitized solar cells: effect of π-bridges on the optoelectronic, and photovoltaic properties.

The dye-sensitized solar cell is a technology unique in its light conversion properties as it operates with record efficiencies in diffused light conditions. The choice of the appropriate sensitizer is one of the important strategies to improve photovoltaic performance of DSSC devices. This theoretical study mainly aims to determine the impact of the π-spacer on the geometric and optoelectronic parameters of sensitizer dyes. For that, we have chosen six organic dyes of Donor-π-Acceptor structure based on triphenylamine unit as electron donor, cyanoacrylic acid as electron acceptor with various π-bridges. The results indicated that the doping process modify dihedral angles and electronic properties by enhancing the planarity and decreasing the gap energy. We have examined the optoelectronic and photovoltaic properties of studied triphenylamine based-dyes. Introducing thiophene and furan as π-spacer groups in D6 dye can effectively decrease the gap energy (Egap = 2.21 eV), broaden the absorption range (λmax = 671.19 nm), and promote the light-harvesting properties. The D2 dye based on two pyrrole units presents an improved electron injection driving force (ΔGinject = - 2.269 eV) and regeneration driving force corresponding to better charge separation. The π-bridge groups can efficiently tune the optoelectronic and photovoltaic properties of sensitizers, which contribute to the efficiency of solar cells. The geometrical and electronic properties of all systems were studied by the DFT method using the correlation exchange functional B3LYP combined with 6-31G(d, p) basis set. On the other hand, the maximum absorption wavelengths λmax and the corresponding oscillator strengths were calculated using the hybrid functional BHandHLYP and 6-31+G(d) basis set. The solvent tetrahydrofuran (THF) are used to study the effect of the solvent, using the "Conductor-Polarizable Continuum" (C-PCM) model. All calculations were performed using Gaussian 09 program.

Effect of aromatic π-bridges on molecular structures and optoelectronic properties of A-π-D-π-A small molecular acceptors based on indacenodithiophene

Investigation on the relationship between molecular structure and device performance is of great important to develop highly efficient A-π-D-π-A small molecular acceptors (SMAs). However, there is still lack of a complete and in-depth study on effects of π-bridge on molecular structure, optoelectronic properties and photovoltaic performances. Herein, we reported the design, synthesis and photovoltaic application of four A-π-D-π-A type SMAs, denoted as IDT-Py-IC , IDT-Fu-IC , IDT-Th-IC , and IDT-Ph-IC , which possess an identical central D unit of indacenodithiophene and the terminal A group of 3-(dicyanomethylidene)indol-1-one, linked by various aromatic π-bridges of pyrrole, furan, thiophene, and benzene, respectively. The impact of the different aromatic π-bridge on molecular structures, optoelectronic and photovoltaic properties as well as active layer morphologies was comprehensively explored. Results show that both molecular co-planarity and electron-donating ability of aromatic π-bridges distinctly affect optical bandgaps ( E g opt ) and HOMO/LUMO levels of these SMAs. The poor backbone planarity of pyrrole-bridged IDT-Py-IC observed by theory calculation leads to a blue-shifted absorption and up-shifted HOMO/LUMO levels. The E g opt of these SMAs is gradually increased and HOMO levels are gradually down-shifted with the decrease of the electron-donating ability of aromatic π-bridges. Polymer solar cells (PSCs) based on these SMAs exhibit a high V oc over 0.93 V, especially for PBDB-T: IDT-Py-IC -based PSCs, producing a rather high V oc up to 1.06 V due to the high-lying LUMO level. After optimizations, the PBDB-T: IDT-Th-IC -based PSC outperforms the other three SMAs with a high PCE up to 8.72% mainly due to the large J sc and FF, which could be ascribed to better absorption characteristics, higher and more proportional carrier mobility, efficient exciton dissociation and charge collection, reduced bimolecular recombination and superior active layer morphology. This finding demonstrates that the π-bridge plays a crucial role in tailoring molecular structures, optoelectronic properties and device performance of A-π-D-π-A type SMAs. • Four A-π-D-π-A SMAs with the same D and A groups, but various π-bridge were developed. • Effect of aromatic π-bridges on structures and optoelectronic properties of SMAs was studied. • Pyrrole-bridged IDT-Py-IC showed a blue-shifted absorption and a high V oc over 1.0 V. • IDT-Th-IC -based PSCs outperformed other three SMAs, along with a high PCE up to 8.72%.

Effect of π-bridges on the performance of indeno[1,2-b]fluorene-based non-fullerene small molecular acceptors

Two non-fullerene acceptors based on the indeno[1,2-b]fluorene central moiety, with selenophene or 2-vinylselenophene as π-bridges and 2-(5,6-difuoro-3-oxo-2,3- dihydro-1H-inden-1-ylidene)malononitrile as end-capping groups, i.e. FICBF-Se and FICBF-SeVi, were synthesized, and the structure-property relationships of the acceptors were systematically studied. The introduction of the vinylene group led to clearly redshifted and broader absorption and a smaller bandgap. FICBF-Se and FICBF-SeVi exhibited optical bandgaps of 1.68 and 1.54 eV, respectively. Solar cells using polymer PBDB-T as a donor and FICBF-Se as an acceptor demonstrated a power conversion efficiency (PCE) of 6.25% with a short-circuit current density (Jsc) of 11.61 mA cm−2. However, the device based on PBDB-T/FICBF-SeVi only delivered a PCE of 3.63% with a Jsc of 9.08 mA cm−2, which should be mainly because the vinylene group decreased the crystallinity and its active layer morphology showed no distinct phase separation.

Effect of furan π-bridge on the photovoltaic performance of D-A copolymers based on bi(alkylthio-thienyl)benzodithiophene and fluorobenzotriazole

The medium band gap donor-acceptor (D-A) copolymer J61 based on bi(alkylthio-thienyl)benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit and thiophene as π-bridge has demonstrated excellent photovoltaic performance as donor material in nonfullerene polymer solar cells (PSCs) with narrow bandgap n-type organic semiconductor ITIC as acceptor. For studying the effect of π-bridges on the photovoltaic performance of the D-A copolymers, here we synthesized a new D-A copolymer J61-F based on the same donor and acceptor units as J61 but with furan π-bridges instead of thiophene. J61-F possesses a deeper the highest occupied molecular orbital (HOMO) level at −5.45 eV in comparison with that (−5.32 eV) of J61 . The non-fullerene PSCs based on J61-F :ITIC exhibited a maximum power conversion efficiency (PCE) of 8.24% with a higher open-circuit voltage ( V oc) of 0.95 V, which is benefitted from the lower-lying HOMO energy level of J61-F donor material. The results indicate that main chain engineering by changing π-bridges is another effective way to tune the electronic energy levels of the conjugated D-A copolymers for the application as donor materials in non-fullerene PSCs.

Novel D-π-A-π-A coumarin dyes for highly efficient dye-sensitized solar cells: Effect of π-bridge on optical, electrochemical, and photovoltaic performance

Abstract The direct connection of coumarin and auxiliary acceptor in D-A-π-A construction will cause large dihedral angle between these two planes, thus affecting the intramolecular charge transfer process. Herein, with an additional π-bridge between coumarin and auxiliary acceptor, two novel coumarin sensitizers, CS-1 and CS-2 , based on D-π-A-π-A construction have been designed and synthesized. With this modification, the planarity of donor-to-auxiliary acceptor part is effectively improved, thus resulting in smoother ICT process and less energy loss. Along with the planarization of molecule, the energy levels of the dyes are also effectively optimized. Moreover, the introduction of additional π-bridge will not affect the photostability of the dye. Accordingly, a record high PCE of 8.03% is obtained by CS-2 sensitized DSSCs, with a J SC of 16.38 mA cm −2 , a V OC of 694 mV, and a ff of 0.707, while only around 3.5% decline in PCE is found after 1000 h aging test. Our results demonstrate that good planarity is obviously preferred to optimize the energy level and photovoltaic performance of sensitizer, providing a powerful strategy for the development of highly efficient organic sensitizers in the future.

Indacenodithiophene-based wide bandgap copolymers for high performance single-junction and tandem polymer solar cells

Two wide bandgap copolymers based on bulky indacenodithiophene (IDT) and alkoxylated benzothiadiazole units (PIDTBTO-T and PIDTBTO-TT) with the thiophene or thieno[3,2-b]thiophene (TT) π-bridge are designed and synthesized. The effect of π-bridge on the π-π packing, optical, carrier transport, nano-sized phase separation and photovoltaic properties of the copolymers are investigated in depth. In comparison with the PIDTBTO-T-based counterpart, the best performance solar cell based on PIDTBTO-TT exhibits a higher power conversion efficiency (PCE) of 8.15% which is mainly attributed to the formation of a fibrous network for the active layer based on PIDTBTO-TT. Furthermore, when a novel hybrid electron transport layer (PDIN:PFN) is introduced into a tandem solar cell using the PIDTBTO-TT-based device and a PTB7-Th-based device as the bottom and top cell components, respectively, the resulting solar cell exhibits an outstanding PCE of 11.15% with a large open circuit voltage of 1.70V. To the best of our knowledge, the PCEs of 8.15% and 11.15% are the highest values reported to date for the single-junction and tandem solar cells using IDT-based copolymers, respectively. Our results demonstrate that the π-bridge modulation is effective in adjusting the charge carrier mobility and photovoltaic performance of IDT-based wide bandgap copolymers for single-junction and tandem devices.

Near-Infrared Asymmetrical Squaraine Sensitizers for Highly Efficient Dye Sensitized Solar Cells: The Effect of π-Bridges and Anchoring Groups on Solar Cell Performance

Conventional squaraine dyes exhibit an intense absorption band in the red region of the solar spectrum and with appropriate design can also have high energy absorption as well, making them interesting building blocks toward achieving panchromatic dyes for dye sensitized solar cell (DSSC) applications. In this report, eight squaraine dyes with thiophene, 4-hexyl-4H-dithieno[3,2-b:2′,3′-d]pyrrole, dithieno[3,2-b:2′,3′-d]thiophene, and 4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b′]dithiophene (DTS) π-bridges with cyanoacetic acid (CA) and cyanophosphonic acid (PA) acceptor/anchoring groups are synthesized to extend the squaraine absorption into the 450–550 nm region and to provide different spatial arrangements of solubilizing groups. Squaraines with CA anchoring groups have higher power conversion efficiencies compared to their PA analogs, with the highest being 8.9% for the DTS-based dye, which is among the highest reported in the literature for squaraine dyes. This is due to high short circuit currents (JSC) and increased open circuit voltages (VOC). Dyes with PA anchoring groups exhibited lower JSC resulting from decreased charge injection efficiency, as determined by femtosecond transient absorption spectroscopy. This study suggests that out-of-plane bulky substituents may increase DSSC performance not only by increasing JSC through decreased aggregation but also by increasing VOC through decreased TiO2/electrolyte recombination.

Insight into quinoxaline containing D–π–A dyes for dye-sensitized solar cells with cobalt and iodine based electrolytes: the effect of π-bridge on the HOMO energy level and photovoltaic performance

Maintaining a balance between the spectral absorption range and driving force for dye regeneration is the key to increase the photovoltaic performance of dye-sensitized solar cells.

Electrochemical Properties of Perylene Diimide (PDI) and Benzotriazole (Btz) Bearing Conjugated Polymers to Investigate the Effect of π-Bridge on Electrochemical Properties

In this study, a series of benzotriazole (BTZ) and perylene diimide (PDI) based copolymers; CoP1 and CoP2 were synthesized via Stille coupling. The effect of perylene diimide (PDI) unit on electrochemical properties of BTZ bearing polymers was investigated. In addition, two different π-bridges: thiophene and dithienopyrrole (DTP) were incorporated into polymer backbone to explore their effects on electrochemical and spectroelectrochemical properties of corresponding polymers; CoP1 and CoP2. Electrochemical and spectral results showed that while CoP1 has only n-type doping property CoP2 has an ambipolar character although p-type doping property is rare for PDI based polymers. Owing to the DTP group, CoP2 showed the lowest band gap reported up to now between perylene diimide derivatives. The effect of different π–bridges and perylene diimide (PDI) unit on the HOMO and LUMO energy levels, optical band gaps, switching time, and optical contrast were presented.

Synthesis and electrochromic properties of triphenylamine containing copolymers: Effect of π-bridge on electrochemical properties

In this study, a series of benzotriazole (BTz) and triphenylamine (TPA)-based random copolymers; poly4-(5-(2-dodecyl-7-methyl-2H-benzo[d][1,2,3]triazol-4-yl)thiophen-2-yl)-N-(4-(5-methylthiophen-2-yl)phenyl)-N-phenylaniline (P1), poly4′-(2-dodecyl-7-methyl-2H-benzo[d][1,2,3]triazol-4-yl)-N-(4′-methyl-[1,1′-biphenyl]-4-yl)-N-phenyl-[1,1′-biphenyl]-4-amine (P2), and poly4-(5′-(2-dodecyl-7-(5-methylthiophen-2-yl)−2H-benzo[d][1,2,3]triazol-4-yl)-[2,2′-bithiophen]-5-yl)-N-(4-(5-methylthiophen-2-yl)phenyl)-N-phenylaniline (P3) were synthesized to investigate the effect of TPA unit and π-bridges on electrochemical and spectroelectrochemical properties of corresponding polymers. The synthesis was carried out via Stille coupling for P1, P3, and Suzuki coupling for P2. Electrochemical and spectral results showed that P1 has an ambipolar character, in other words it is both p-type and n-type dopable, whereas P2 and P3 have only p-doping property. Effect of different π-bridges and TPA unit on the HOMO and LUMO energy levels, switching time, and optical contrast were discussed. All polymers are promising materials for electrochromic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 537–544