Evaluation of bis-dicyanovinyl short-chain conjugated systems as donor materials for organic solar cells (original) (raw)
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Simple and Versatile Molecular Donors for Organic Photovoltaics Prepared by Metal-Free Synthesis
Chemistry - A European Journal, 2014
Donor-acceptor molecules (D-p-A) built by connecting a diphenylhydrazone block to a dicyanovinyl acceptor group via various thiophene-based p-conjugating spacers (1-5) were synthesized from mono-or dialdehydes by a simple metal-free procedure. Cyclic voltammetry and UV/ Vis absorption spectroscopy show that the extension and/or increase of the donor strength of the spacer produces a decrease of the HOMO and LUMO energy level, a red shift of the absorption spectrum and an increase of the molecular absorption coefficient. Compared to solutions, the optical spectra of spin-cast thin films of compounds 1-3 show a broadening and red shift of the absorption bands, consis-tent with the formation of J-aggregates. In contrast the blue shift observed for the EDOT-containing compounds 4 and 5 suggests the presence of H-aggregates. Solution-cast and vacuum-deposited films of donors 1-5 were evaluated in solar cells with fullerene C 60 as acceptor. A power-conversion efficiency among the highest reported for bilayer devices of basic configuration was obtained with compound 2. On the other hand, the results obtained with 4 and 5 suggest that the presence of EDOT in the structure can have deleterious effects on the organization and performances of the donor material.
Small Molecular Donors for Organic Solar Cells Obtained by Simple and Clean Synthesis
ChemSusChem, 2014
A small donor-acceptor molecule is synthesized in a two-step procedure involving reaction of N,N-diphenylhydrazine on 2,5diformylthiophene and Knoevenagel condensation. Results of UV/Vis absorption spectroscopy and cyclic voltammetry show that replacement of the phenyl ring bridge of a reference compound 2 by an azo group produces a slight red-shift of l max , an enhancement of the molecular absorption coefficient, and a decrease of the energy level of the frontier orbitals. A preliminary evaluation of the potentialities of compound 1 as donor material in a basic bilayer planar heterojunction cell of 28 mm 2 active area using C 60 as acceptor gave a short-circuit current density of 6.32 mA cm À2 and a power conversion efficiency of 2.07 %.
Dyes and Pigments, 2018
Structural modification of benzo[c]-1,2,5-thiadiazole (BT) has been proved to be the prominent way to fine-tune the frontier energy levels and the intermolecular and intramolecular interactions in organic conjugated materials. In this study, a new acceptor unit, alkyl benzo[c][1,2,5]thiadiazole-5-carboxylate (BT-Est), was designed and synthesized by drafting mono alkoxy-carboxylate substituent on 5-position of BT core. Its compatibility in the conjugated system was investigated by co-polymerizing BT-Est with well-known benzo[1,2-b:4,5-b']dithiophene monomers containing either 2-(2ethylhexyl)thienyl or 2-((2-ethylhexyl)thio)thienyl side chains to form two new polymers, P1 and P2, respectively. The BT-Est yielded polymers with good solubility, medium bandgap (~1.71 eV), and deep highest occupied molecular orbital energy levels (−5.48 to −5.54 eV). Among the polymers, P1 exhibited broader absorption, compact molecular packing, high charge carrier mobility, and effective exciton dissociation, despite of the torsion angle caused by the free rotation of the carboxylate group in the polymer backbone. Consequently, the best power-conversion efficiency of 6.9%, with a J SC of 14.6 mA cm −2 , V OC of 0.9 V, and FF of 52.5% were obtained for P1-based devices with the well-known non-fullerene acceptor ITIC. We systematically expounded the structureproperty relationship of the BT-Est polymers using diverse characterization methods. Our results demonstrated that the mono carboxylate-substitution on the BT core can be used as the alternate strategy to modulate the optoelectronic properties and control the aggregation in the conjugated polymers. Thus, BT-Est has the potential to produce new donor-acceptor conjugated polymers and small molecules for application in organic electronics.
Dyes and Pigments, 2012
Bulk heterojunction (BHJ) photovoltaic devices were fabricated from the blends of compounds BTD-TNP (electron donor) and P-A (electron acceptor) and characterized through current-voltage measurements under illumination. Compound BTD-TNP contains dithyenyl-benzothiadiazole central unit and cyanovinylene-p-nitrophenyl terminal moieties. Compound P-A is a symmetrical perylene-anthracene diimide with tert-butylphenoxy side groups at the 1,7-bay positions. Both the absorption spectra and the incident photon to the current conversion efficiency (IPCE) spectra of the device were extended up to 800 nm. A power conversion efficiency of 2.85% with short-circuit current density of 6.8 mA/cm 2 , open-circuit voltage of 0.88 V and fill factor of 0.47 were obtained. It was found that the hole and electron mobility in the active layer were about 4.6 Â 10 À5 and 8.8 Â 10 À4 cm 2 /Vs, respectively, which indicates the fairly balanced charge transport in the device.
A new organic small molecule, 2-((10-(6-(3,6-di-tert-butyl-9H-carbazole-9-yl)hexyl)-10H-phenothiazine-7-yl)methylene) malononitrile named CSORG5 has been synthesized and successfully applied for organic bulk heterojunction (BHJ) solar cells as a novel electron acceptor along with P3HT as a donor. The CSORG5 molecule possess facile synthesis, solution processability, visible light absorption, a properly matched lowest unoccupied molecular orbital (LUMO) energy level with conjugated polymers and moderate electron mobility, making the molecule an ideal acceptor for P3HT and other low band gap conjugated polymers. The BHJ organic solar cell constructed from a P3HT : CSORG5 (1 : 1) active layer processed from a DIO/THF solvent, exhibits a high open circuit voltage of up to 0.98 V resulting in an overall power conversion efficiency of 2.80%. Furthermore, the PCE is enhanced up to 4.16% when a thin layer of TiO 2 is inserted between the active layer and the Al electrode.
Donor–acceptor–acceptor–donor small molecules for solution processed bulk heterojunction solar cells
Organic Electronics, 2015
We report on the optical and electrochemical characterization (experimental and theoretical) of two donor substituted benzothiadiazole with different cyano based acceptor p-linkers, tetracyanobutadiene (TCBD) SM1 and dicyanoquinomethane (DCNQ) SM2, and explore them as the donor component for solution processed bulk heterojunction organic solar cells, along with PC 71 BM as the electron acceptor. The solution bulk heterojunction (BHJ) solar cells based on dichloromethane (DCM) processed active layer with SM1 and SM2 as donor and PC 71 BM as acceptor achieve power conversion efficiency (PCE) of 2.76% and 3.61%, respectively. The solar cells based on these two small molecules exhibit good Voc, which is attributed to their deep HOMO energy level. The higher PCE of the device based on SM2 compared to SM1 is attributed to the its small bandgap, broader absorption profile and enhanced hole mobility. Additionally, the PCE of the SM2:PC 71 BM based solar cells processed with 1-chloronaphthalene CN (3 v%)/DCM is further improved reaching upto 4.86%. This increase in PCE has been attributed to the improved nanoscale morphology and more balanced charge transport in the device, due to the solvent additive.
Organic Electronics, 2015
Two benzothiazole (BT) based donor-acceptor-p-acceptor (D-A-p-A) molecular system denoted as BT3 and BT4 have been designed, synthesized and their optical and electrochemical properties were investigated. The BT4 show wider absorption profile and lower bandgap as compared to BT3 due to the strong electron withdrawing ability of dicyanoquinodimethane (DCNQ) as compared to tetracyanobutadiene (TCBD). The solution processed bulk heterojunction solar cells were fabricated using BT3 and BT4 as electron donor and PC 71 BM as electron acceptor. The organic solar cells optimized dichloromethane (DCM) processed BT3:PC 71 BM (1:1) and BT4:PC 71 BM (1:1) showed PCE of 2.56% and 3.68%, respectively. The higher PCE of BT4:PC 71 BM is related to the wider absorption of the blend and better ordered domain sizes in the blend as compared to BT3:PC 71 BM. The devices processed with 1,8-diiodoctane (DIO) additives showed PCE of 3.77% and 5.27%, for BT3:PC 71 BM and BT4:PC 71 BM blends, respectively.
European Journal of Organic Chemistry, 2015
We describe the detailed syntheses and characterization of two new electron-donor molecules based on an acceptor-donor-acceptor (A-D-A) structure with carbazole as the electron-rich building block, benzothiadiazole (BT) as the electron-acceptor building block and octylrhodanine as the end group. We also examined the effects of a thiophene group as a spacer between the BT and the carbazole units on the optoelectronic, morphological and photovoltaic properties.
Synthetic Metals, 2019
Three novel molecules based on thiophene-fused 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) units linked through functionalized π-conjugated arene bridges are synthesized by three-step sequence of Sonagashira coupling, double thioannulation and Knoevenagel condensation. The energy of their frontier orbitals shows that these molecules are suitable for replacing fullerenes as electron acceptors in composites with conjugated donor polymers used in organic photovoltaics (OPV). The composite of polymer donor PCDTBT with fluorene-linked thiophene-fused TCAQs demonstrates good solubility in organic solvents and bulk heterojunction morphology with characteristic donor and acceptor domain size of several tens of nanometers, favourable for photoelectric conversion. This composite also exhibits prominent light-induced EPR signal indicating efficient photoinduced free charge generation. OPV devices based on this composite were fabricated by vacuum-free method. They show photoelectric conversion with maximum PCE of 0.71%.
Journal of Molecular Modeling, 2020
A series of twelve Acceptor-π-Donor-π-Acceptor (A-π-D-π-A) topology-based donor molecules, where diketopyrrolopyrrole (DPP) as donor core unit is connected through furan which acts as conjugated π-bridge (CB) to aromatic derivatives (Ar) as acceptor units, have been investigated by making substitutions in acceptor units by using density functional theory(DFT) and time-dependent density functional theory (TD-DFT) for organic solar cell applications. The comparative study of optoelectronic properties indicates that thiadiazole with pyridine units containing molecules (M6b) exhibit lower energy of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels than those of oxadiazole and pyridine containing units (M6b). Among our investigated donors, the smallest Eg of 1.60 eV was observed for both M6a and M6b with distinctive broad absorption at 843 and 857 nm, respectively. Overall, smaller electron transfer (λ e) values in contrast to hole transfer (λ h) demonstrate that these donor compounds would be best for λ e. The calculated open circuit voltage (Voc) is 2.45 and 2.17 eV, regarding bisPCBM and PC60BM (phenyl-C61-butyric acid methyl ester) acceptors. Thus, these theoretical calculations not only endorse the deep consideration between the chemical structures and optoelectronic characteristics of the donor-acceptor systems but also suggest appropriate materials for high-performance Organic Photovoltaics (OPV).