Effects of solvent additive on "s-shaped" curves in solution-processed small molecule solar cells.

A novel molecular chromophore, p-SIDT(FBTThCA8), is introduced as an electron-donor material for bulk heterojunction (BHJ) solar cells with broad absorption and near ideal energy levels for the use in combination with common acceptor materials. It is found that films cast from chlorobenzene yield devices with strongly s-shaped current-voltage curves, drastically limiting performance. We find that addition of the common solvent additive diiodooctane, in addition to facilitating crystallization, leads to improved vertical phase separation.

Highly Twisted Dianchoring D-π-A Sensitizers for Efficient Dye-Sensitized Solar Cells.

Two new organic dyes-BPDTA and BTTA-possessing dual D-π-A units have been synthesized, characterized, and employed as efficient sensitizers for dye-sensitized solar cells. The two individual D-π-A, which are based on (E)-3-(5'-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)-[2,2'-bithiophen]-5-yl)-2-cyanoacrylic acid unit (D21L6), are connected directly between phenylene or thiophene within linear π-conjugated backbone to constitute a highly twisted architecture for suppressing the dye aggregation. The new dianchoring dyes exhibited pronounced absorption profile with higher molar extinction coefficient, which is consistent with the results obtained from density functional theory (DFT) calculations.

Regioisomeric Effects of Donor-Acceptor-Acceptor' Small-Molecule Donors on the Open Circuit Voltage of Organic Photovoltaics.

Donor-acceptor-acceptor' small-molecule donors are synthesized to investigate regioisomeric effects on organic photovoltaic device performance. Cross-conjugation in 2-((7-(N-(2-ethylhexyl)-benzothieno[3,2-b]thieno[3,2-d]pyrrol-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)malononitrile leads to an increased open-circuit voltage compared with its isomer 2-((7-(N-(2-ethylhexyl)-benzothieno[3,2-b]thieno[2,3-d]pyrrol-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)malononitrile. A correlation is then established between molecular conjugation length and orbital energies, and hence open-circuit voltage.

Cofacial Versus Coplanar Arrangement in Centrosymmetric Packing Dimers of Dipolar Small Molecules: Structural Effects on the Crystallization Behaviors and Optoelectronic Characteristics.

Two D-π-A-A molecules (MIDTP and TIDTP) composed of an electron-rich ditolylamino group (D) and an electron-deficient 5-dicyanovinylenylpyrimidine (A-A) fragment bridged together with indeno[1,2-b]thiophene (IDT) were synthesized. These molecules provide an opportunity to examine in-depth the impact of side-chain variations (methyl vs p-tolyl) on the crystallization behaviors, solid-state morphology, physical properties, and optoelectronic characteristics relevant for practical applications. X-ray analyses on single-crystal structures indicate that methyl-substituted MIDTP forms "coplanar antiparallel dimers" via C-H···S interactions and organizes into an ordered slip-staircase arrays.

Regioisomeric effects on the electronic features of indenothiophene-bridged D-π-A'-A DSSC sensitizers.

Two D-π-A'-A regioisomers (A-IDT-D and D-IDT-A) featuring 4,4'-di-p-tolyl-4 H-indeno[1,2-b]-thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine-cyanoacrylic acid acceptor (A'-A) have been successfully synthesized and characterized as efficient sensitizers for the dye-sensitized solar cells (DSSCs). The different arrangements of the D and A'-A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A-IDT-D) or opposite (D-IDT-A) to the direction of intramolecular (donor-to-acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade-off between the molar extinction coefficient (ε) and the S0 →S1 transition energy.

Indolo[2,3-b]carbazole synthesized from a double-intramolecular Buchwald-Hartwig reaction: its application for a dianchor DSSC organic dye.

A new synthetic strategy for indolo[2,3-b]carbazole via a double-intramolecular Buchwald-Hartwig reaction has been established. The N-alkylated indolo[2,3-b]carbazole then was adopted as the geometry-fixed core for the synthesis of a new molecule (ICZDTA) bearing two bithiophene π-bridged 2-cyanoacrylic acid groups as the bidentate anchor. The bidentate anchoring together with efficient HOMO (indolo[2,3-b]carbazole) → LUMO (TiO2 nanocluster) electron transfer leads to the successful development of ICZDTA-based DSSC with a power conversion efficiency of 6.

Benzochalcogenodiazole-based donor-acceptor-acceptor molecular donors for organic solar cells.

Four new molecules with a donor-acceptor-acceptor (D-A-A) configuration, in which 2,1,3-benzoxadiazole or 2,1,3-benzoselenodiazole were adopted as the central bridging acceptor, were synthesized as electron donors for small-molecule organic solar cells. In conjunction with two previously reported 2,1,3-benzothiadiazole-based compounds, the influences of the benzochalcogenodiazole acceptor unit and the ditolylarylamine donor moiety on the molecular structure, electrochemical behavior, and optical properties of the materials were investigated systematically to obtain a clear structure-property relationship. Vacuum-deposited hybrid planar mixed-heterojunction devices fabricated with the new donors and C70 as the acceptor showed power conversion efficiencies in the range of 2.

A novel amine-free dianchoring organic dye for efficient dye-sensitized solar cells.

An amine-free oligothiophene-based dye (BTB) featuring a tailor-made dianchoring function, a spiro-configured central unit, and bulky end-capping TIPS groups to diminish intermolecular interactions and to suppress aggregation-induced self-quenching was synthesized to achieve efficient dye-sensitized solar cells with a high power conversion efficiency of 6.52%.

Cationic iridium complexes with intramolecular π-π interaction and enhanced steric hindrance for solid-state light-emitting electrochemical cells.

Cationic iridium complexes incorporated 4,5-diaza-9,9'-spirobifluorene as N(∧)N ancillary ligands, in which one (2) or two (3) phenyl groups were introduced onto 4,5-diazafluorene to afford intraligand π-π interactions. The X-ray crystal structures of complexes 2 and 3 show that the pendant phenyl ring forms strong intramolecular face-to-face π-stacking with the difluorophenyl ring of the cyclometalated ligand with distances of 3.38 Å for complex 2 and 3.

A low-energy-gap organic dye for high-performance small-molecule organic solar cells.

A novel donor-acceptor-acceptor (D-A-A) donor molecule, DTDCTB, in which an electron-donating ditolylaminothienyl moiety and an electron-withdrawing dicyanovinylene moiety are bridged by another electron-accepting 2,1,3-benzothiadiazole block, has been synthesized and characterized. A vacuum-deposited organic solar cell employing DTDCTB combined with the electron acceptor C(70) achieved a record-high power conversion efficiency (PCE) of 5.81%.

Design and synthesis of iridium bis(carbene) complexes for efficient blue electrophosphorescence.

Five iridium bis(carbene) complexes, [Ir(pmi)(2)(pypz)] (1), [Ir(mpmi)(2)(pypz)] (2), [Ir(fpmi)(2)(pypz)] (3), [Ir(fpmi)(2)(pyim)] (4), and [Ir(fpmi)(2)(tfpypz)] (5) (pmi=1-phenyl-3-methylimdazolin-2-ylidene-C,C(2'); fpmi=1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C,C(2'); mpmi=1-(4-methyl-phenyl)-3-methylimdazolin-2-ylidene-C,C(2'); pypz=2-(1H-pyrazol-5-yl)pyridinato; pyim=2-(1H-imidazol-2-yl)pyridinato; and tfpypz=2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato), were synthesized and their structures were characterized by NMR spectroscopy, mass spectroscopy and X-ray diffraction. These complexes showed phosphorescent emission with the emission maxima between 453 and 490 nm. Various spectrophotometric measurements, cyclic voltammetric studies, and density functional theory (DFT) calculations show that, unlike most of the phosphorescent cyclometalated iridium complexes, the lowest unoccupied molecular orbital (LUMO) energy and the emissive state of these iridium complexes are mainly controlled by the N,N'-heteroaromatic (N^N) ligand.

Electrochemistry and electrogenerated chemiluminescence of a spirobifluorene-based donor (triphenylamine)-acceptor (2,1,3-benzothiadiazole) molecule and its organic nanoparticles.

A new D-A-π-A-D molecule (Spiro-BTA) containing two 2,1,3-benzothiadiazole (BTA) as the acceptor (A) and triphenylamine as the donor (D) bridged by a spirobifluorene moiety has been synthesized. The novel D-A molecule shows intense red emission (612 nm) with a high PL quantum yield (Φ(PL) = 0.51) in a solid film.

Organic dyes containing coplanar diphenyl-substituted dithienosilole core for efficient dye-sensitized solar cells.

Two new organic dyes adopting coplanar diphenyl-substituted dithienosilole as the central linkage have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). The best DSSC exhibited a high power conversion efficiency up to 7.6% (TP6CADTS) under AM 1.