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Two quinoxaline-based conjugated polymers were successfully synthesized for application in polymer solar cells (PSCs). The quinoxaline unit with an electron-donating dimethylamino substituent was used as the electron-accepting (A) moiety, whereas indacenodithiophene (IDT) and indacenodithieno-thiophene (IDTT) were chosen as the electron-donating (D) groups to synthesize D-A type conjugated polymers. To investigate the photovoltaic properties of the polymers, an inverted-type device with the configuration of ITO/ZnO/polymer:PC71BM/MoO3/Ag was fabricated. It has been observed that the overall performances of the organic photovoltaic cells were significantly improved by changing the electron-donating components from IDT to IDTT. Therefore, this study can provide insights into the design and structure–property correlation of quinoxaline-based conjugated polymers for PSCs. [ABSTRACT FROM AUTHOR]

We have synthesized two acceptor-donor-acceptor (A-D-A) type quinoxaline-based small molecules for organic photovoltaic cells (OPVs). To construct the A-D-A architecture, the electron-accepting quinoxaline derivative (Qx) was attached on both ends of the electron-donating benzodithiophene (BDT) unit via the Stille coupling reaction. After the confirmation of the structural features, the optical and electrochemical characteristics and the photovoltaic properties of the two small molecules were investigated. A typical inverted-type device with the configuration of ITO/ZnO/small molecules: PC71BM/MoO3/Ag was fabricated and examined. It has been observed that the performances of OPVs were improved by the incorporation of the additional thiophene linkage between the BDT and Qx moieties. Therefore, this study can provide insights into the design and structure–property correlation of quinoxaline-based organic small molecules for OPVs [ABSTRACT FROM AUTHOR]

Reduction of a Schottky barrier between the active layer and electrodes can play an important role enhancing the power conversion efficiency (PCE) of organic solar cells (OSCs), which originated from a favorable interface dipole at the cathode interface. Herein, two new small molecules (SM) electrolytes based on tosylate anions, named 2,2'-(ethane-1,2-diylbis(oxy))bis(N,N,N-trimethylethananminium) benzenesulfonate (TEG-M-OTs) and 1,1'-bis(1-dodecyl)-4,4′-bipyridine-1,1′-diium benzenesulfonate (V-C12-OTs), were synthesized to induce the reduction of a Schottky barrier in OSCs. The PCE of devices based on ZnO with TEG-M-OTs or V-C12-OTs as the cathode buffer layer (CBL) was enhanced from 7.48% to 7.74% and 7.88%. In case of ZnO-free devices, the PCE of TEG-M-OTs or V-C12-OTs was achieved up to 4.22% and 6.95%, respectively. The Kelvin probe microscopy was performed by measuring the work function (WF) of SM electrolytes with or without ZnO on the ITO surface. It showed that the WFs of SM electrolytes coated ITO are closer to - 4.02 eV, the lowest unoccupied molecular orbitals (LUMO) of the acceptor, than the WF of MeOH treated ITO with ZnO (- 4.37 eV). [ABSTRACT FROM AUTHOR]

Two D-A-D type quinoxaline-based small molecules have been synthesized by Suzuki coupling reaction for solution-processable organic photovoltaic cells (OPVs). The electron-donating triphenylamine was connected to both ends of an electron-withdrawing 2,3-diphenylquinoxaline core through thiophene bridge to produce QxTPA. In addition, QxCF3TPA was formed by introducing strong electron-withdrawing trifluoromethyl (CF3) groups into the para-position of the phenyl ring at the 2,3-position of quinoxaline core in QxTPA to explore their effect on the various properties of small molecules. The finding revealed the significant contributions of CF3 substituents in enhancing the photovoltaic performances of OPVs with QxCF3TPA compared to the reference case with QxTPA. [ABSTRACT FROM AUTHOR]

Abstract: A series of quinoxaline‐based conjugated polymers, in which the electron‐donating benzodithiophene (BDT) unit is linked to the electron‐accepting 6,7‐difluorinated quinoxaline (DFQ) derivatives by a thiophene bridge, is synthesized. To investigate their effects on the intrinsic properties of polymers, strong electron‐withdrawing trifluoromethyl (CF3) groups were incorporated into the meta‐position of the phenyl ring at the 2,3‐positions of the DFQ unit of the reference polymer, labelled PEhB‐FQx, to yield the target polymer PEhB‐FQxCF3. In addition, the 2‐ethylhexyloxy substituents on the BDT donor in PEhB‐FQxCF3 are changed to the more planar 2‐ethylhexyl thiophene units to produce another target polymer PThB‐FQxCF3. Owing to the significant contributions of the CF3 moiety, PEhB‐FQxCF3 exhibits quite discernible optical and electrochemical properties along with significant enhancement in photovoltaic performances compared to the reference polymer PEhB‐FQx. Furthermore, the incorporation of the alkylthienyl side chains on the BDT moiety confers on the resultant PThB‐FQxCF3 to possess the maximum power conversion efficiency of 7.26% with an open circuit voltage of 0.88 V, short‐circuit current density of 12.20 mA cm−2, and fill factor of 67.80%. [ABSTRACT FROM AUTHOR]

A series of small molecules (SMs) containing fluorinated benzothiadiazole (BT) and phenothiazine (PT) were synthesized via the Suzuki coupling reaction. For exploring the effect of auxiliary electron-accepting moieties on the chemical structures, one or two fluorine atoms were selectively incorporated into the central electron-withdrawing BT unit of the non-fluorinated standard small molecule (BDP) to affordBDP-FandBDP-FF, respectively. Because of the favorable contributions of the fluorine atoms, the optimized inverted-type photovoltaic devices containing the SMs as active components exhibited improvement in PCE with increasing fluorine substitution, i.e., 0.49%, 0.54%, and 0.78% forBDP, BDP-F, andBDP-FF, respectively. [ABSTRACT FROM AUTHOR]

Polymer acceptors based on perylene diimide (PDI) with three symmetrical S-heteroacene backbone units of different sizes were synthesized for use in all-polymer solar cells (all-PSCs). The effects of varying the size of the heteroacene unit on the backbone of the PDI polymer are evident in the absorption spectra and their energy level offsets, which are correlated with their morphological and photovoltaic properties. These newly synthesized polymers were employed as acceptors with the polymer poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) as the donor in all-PSCs that were found to exhibit modest power conversion efficiencies. The variations in photovoltaic properties of all-PSCs are investigated by characterizing the charge generation, carrier mobilities and recombination. The morphological disorder at the polymer/PPDT2FBT interface and average composition variations are revealed by using grazing incidence wide angle X-ray scattering (GIWAXS) and resonance soft X-ray scattering (R-SoXS) characterizations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Low band gap polymers based on 2,1,3-benzooxadiazole and thiophene. [•] Effect of number of thiophen rings on the optical, electrochemical, and photovoltaic property. [•] The open circuit voltage is dependent on the HOMO energy of the polymer. [ABSTRACT FROM AUTHOR]

Abstract A series of new acceptor-donor-acceptor (A-D-A) type conjugated small-molecule-dyes based on indacenodithieno[3,2- b ]thiophene (IDTT) and 2-(2-methyl-4 H -chromen-4-ylidene)malononitrile (CMCN), named IDTT-CMCN and IDTT-HT-CMCN , have been synthesized for application in organic solar cells. A-D-A type small-molecules with CMCN can effectively form a powerful push-pull structure that induces effective intramolecular charge transport (ICT) and enhanced optical absorption. In comparison with IDTT-CMCN , IDTT-HT-CMCN has 3-hexylthiophene (HT) as a π-bridge unit between the IDTT and CMCN moieties to increase the solubility and extend the π-conjugation length. The resulting dye (IDTT-HT-CMCN) with a hexylthiophene ring as a π-bridge showed a smaller band gap and better solubility. Thus, a power conversion efficiency (PCE) as high as 7.60% was achieved with a short circuit current of 12.7 mA/cm2, open circuit voltage of 0.94 V, and fill factor of 63.8%. To the best of our knowledge, small-molecule-based donors with CMCN as an electron-withdrawing unit have never been reported before. In addition, the PCE of 7.60% reported in this work is highly efficient among the PCE reported for an organic solar cell using an IDTT -based small-molecule-donor material. Graphical abstract Image 1 Highlights • A series of new conjugated small-molecule-donors were synthesized. • Chromone malononitrile (CMCN) as the electron-withdrawing group. • The PCE of OSCs accomplished was reached up to 7.6%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel methodology to obtain soluble solid-state metal oxide precursor (PTO). • Highly pure, stable and monodispersed PTO was obtained. • PTO exhibits excellent solution processibility and optical/electrical properties. • Optoelectronic devices made with PTO provides improved performance and stability. Metal suboxides (MOs) are among the most attractive interfacial materials owing to their outstanding functionality and excellent electrical and optical properties. However, the limitations of solution processability and ambient stability of the precursor hinder their widespread application. In this study, we developed a novel methodology for the solidification of sol–gel-derived MO-based organic complexes without affecting the properties of the MO products. By controlling the polarity of a conventional sol–gel derived titanium suboxide solution (STO) with organic functional side groups, we can easily obtain a nearly monodispersed solid-state precursor of STO (PTO) with excellent solubility in alcohols. PTO demonstrates ideal optical and electrical properties as an electron transport layer (ETL) with a significantly enhanced stability due to the elimination of the reactive residue. Owing to the optical, electrical, and excellent film-forming properties of PTO, organic and perovskite solar cells with PTO exhibit drastically improved performances and stability. Thus, a PTO-based ETL was successfully fabricated on various active layers, including those prepared from organic and perovskite materials, demonstrating the universality of PTO. [ABSTRACT FROM AUTHOR]

Highlights: [•] The work function ZnO can be tuned by the self assembled monolayer. [•] SAM treated ZnO used as an electron transporting layer for inverted solar cells. [•] The direction of interface dipole depends on the dipole orientation of SAM molecules. [•] The photovoltaic parameters depend on the dipole orientation of SAM molecules. [Copyright &y& Elsevier]

Abstract: In order to improve the performance and mechanical flexibility of the transparent conducting electrodes (TCEs) for organic photovoltaics, we proposed a flexible PEDOT:PSS/ITO hybrid TCE. A conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was introduced as a buffer layer beneath the ITO film. This PEDOT:PSS/ITO hybrid electrode showed a sheet resistance of 85Ω/sq, which was much better than that of a single-layer ITO film. The mechanical integrity of the flexible PEDOT:PSS/ITO hybrid electrode was investigated by bending and fragmentation tests. The failure bending radius was lower in bending tests of the PEDOT:PSS/ITO electrode than for the ITO electrode due to buffering effect of PEDOT:PSS film. A fragmentation test showed superior stretchability and better interfacial adhesion strength for the PEDOT:PSS/ITO hybrid electrode on a PET substrate than for the ITO electrode. We have prepared flexible organic photovoltaic (OPV) devices using the PEDOT:PSS/ITO hybrid TCE. The flexible OPV device fabricated using the PEDOT:PSS/ITO hybrid anode exhibited a power conversion efficiency of 3.21% (FF=0.45, V oc=0.72V), which is comparable with that using an ITO anode. A bending test of the OPV device also showed better mechanical bending and crack-resistance performances for the OPV device with the PEDOT:PSS/ITO hybrid anode than for the ITO anode. The comparable performance and superior flexibility of flexible OPVs with an PEDOT:PSS/ITO hybrid anode indicates that the PEDOT:PSS/ITO hybrid electrode is a promising flexible electrode scheme for next generation flexible photovoltaic devices. [Copyright &y& Elsevier]

Abstract: Hybrid carbon nanotubes–bimetallic composite nanoparticles with sea urchin-like structures (SU-CNTs) were introduced to bulk heterojuction polymer-fullerene solar cells to improve their performance. The SU-CNTs were composed of multi-walled CNTs, which were grown radially over the entire surface of the bimetallic nanoparticles composed of Ni and Al. SU-CNTs with a precisely controlled length of ∼200±40nm were dispersed homogenously in a polymer active layer. Compared with a pristine device (i.e., without SU-CNTs), the SU-CNTs-doped organic photovoltaic (OPV) cells showed an improved short-circuit current density and power conversion efficiency from 7.5 to 9.5mA/cm2 and 2.1±0.1% to 2.2±0.2% (max. 2.5%), respectively. The specially designed SU-CNTs have strong potential as an effective exciton dissociation medium in the polymer active layer to enhance the performance of organic solar cells. [Copyright &y& Elsevier]

A new approach is presented here to maximize the efficiency of ternary blend polymer solar cells (ter-PSCs). The properties of co-absorbing wide band-gap polymers are fine-tuned via the insertion of two different appropriate electron-acceptor units on their backbone in different ratios, and the resulting polymers are utilized as a co-absorbent on ter-PSCs. The copolymerization of benzodithiophene, pyrrolopyrrole-1,3-dione, and difluoro-benzothiadiazole derivatives at three different ratios, 1.00:1.00:0.00, 1.00:0.50:0.50, and 1.00:0.25:0.75, produces the polymers P1–P3. The absorption bands of P1–P3 are gradually red-shifted, and the band-gaps are reduced. The crystallinity of the polymers is increased in the order of P1 < P2 < P3. The binary polymer solar cells (bi-PSCs) are fabricated using blends of P1 , P2, or P3 with PC 70 BM and provide comparable power conversion efficiencies (PCE s) of 5.41%, 5.55%, and 4.01%, respectively. However, the inclusion of 20 wt% of each of P1 , P2 , and P3 on a P4 (=PTB7-Th):PC 70 BM blend offers PCE s of 9.31%, 9.60%, and 9.85%, respectively, which are higher than that of the bi-PSC made using a blend of P4:PC 70 BM (PCE = 8.20%). The improved absorption, crystallinity, and carrier mobilities of the ternary blends are the main reasons for their enhanced photovoltaic performance compared with the binary blends. Image 1 • The properties of co-absorbing polymers were tuned via main chain modification. • The band-gaps of co-absorbing polymers were varied between 2.11 and 1.71 eV. • The HOMO levels of co-absorbing polymers were varied between −5.38 and −5.26 eV. • The binary PSCs properties of co-absorbing polymers were comparable. • Each co-absorbing polymers displayed different performance on ternary PSCs. [ABSTRACT FROM AUTHOR]