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A series of small‐molecule‐based hole‐transporting materials (HTMs) featuring a 4H‐cyclopenta[2,1‐b : 3,4‐b′]dithiophene as the central core with triphenylamine‐ and carbazole‐based side groups was synthesized and evaluated for perovskite solar cells. The correlations of the chemical structure of the HTMs on the photovoltaic performance were explored through different combinations of the central π‐bridge moieties. The optical and electrochemical properties, energy levels, and hole mobility were systematically investigated, revealing the significant influence of the central core planarity and packing structure on their photovoltaic performance. The optimized device based on CT1 exhibited a PCE (power conversion efficiency) of 17.71 % with a device architecture of FTO/TiO2 compact layer/TiO2 mesoporous/CH3NH3PbI3/HTM/MoO3/Ag, which was found to be on par with that of a cell fabricated based on state‐of‐the‐art spiro‐OMeTAD (16.97 %) as HTM. Moreover, stability assessment showed an improved stability for CPDT‐based HTMs in comparison with spiro‐OMeTAD over 1300 h. Four HTMs based on cyclopenta[2,1‐b;3,4‐b′]dithiophene core are designed and applied for lead perovskite (MAPbI3) solar cells. PSCs based on CT1 as HTM afford an impressive power conversion efficiency of 17.71 %. The devices based on the CT1 presented significantly higher stability than the device based on spiro‐OMeTAD. [ABSTRACT FROM AUTHOR]

ABSTRACT Two D-π-A copolymers, based on the benzo[1,2- b:4,5- b′]-dithiophene (BDT) as a donor unit and benzo-quinoxaline (BQ) or pyrido-quinoxaline (PQ) analog as an acceptor (PBDT-TBQ and PBDT-TPQ), were designed and synthesized as a p-type material for bulk heterojunction (BHJ) photovoltaic cells. When compared with the PBDT-TBQ polymer, PBDT-TPQ exhibits stronger intramolecular charge transfer, showing a broad absorption coverage at the red region and narrower optical bandgap of 1.69 eV with a relatively low-lying HOMO energy level at −5.24 eV. The experimental data show that the exciton dissociation efficiency of PBDT-TPQ:PC71BM blend is better than that in the PBDT-TBQ:PC71BM blend, which can explain that the IPCE spectra of the PBDT-TPQ-based solar cell were higher than that of the PBDT-TBQ-based solar cell. The maximum efficiency of PBDT-TPQ-based device reaches 4.40% which is much higher than 2.45% of PBDT-TBQ, indicating that PQ unit is a promising electron-acceptor moiety for BHJ solar cells. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1822-1833 [ABSTRACT FROM AUTHOR]

Two fused-thiophene-containing ruthenium sensitizers, [Ru(Hdcbpy)(ottip)(NCS)2]- ·0.5[H]+ ·0.5[N(C4H9)4]+ [ Z1, H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine, ottip = 2-(5-octylthieno[3,2- b]thiophen-2-yl)-1 H-imidazo[4,5- f][1,10]phenanthroline] and [Ru(Hdcbpy)(odttip)(NCS)2]- ·0.5[H]+ ·0.5[N(C4H9)4]+ { Z2, odttip = 2-[6-octyldithieno(3,2- b:2′,3′)thiophen-2-yl]-1 H-imidazo[4,5- f][1,10]phenanthroline}, were designed for use in dye-sensitized solar cell (DSSC) applications. The fused-thiophene-based Z1 and Z2 have stronger light-harvesting capabilities compared with a non-fused-thiophene analog, [Ru(Hdcbpy)(otip)(NCS)2]- ·0.5[H]+ ·0.5[N(C4H9)4]+ [ JF-2t, otip = 2-(5-octylthiophen-2-yl)-1 H-imidazo[4,5- f][1,10]phenanthroline], and a standard N3 dye. The power-conversion efficiency of the Z1- and Z2-sensitized solar cells were superior (8.70 % and 8.15 %) to JF-2t- and N3-sensitized solar cells (7.85 and 7.40 %, respectively) under standard AM1.5G full sunlight irradiation. The photovoltaic performance of Z1 was better than Z2, primarily owing to the fact that Z1-based cells have a higher level of dye loading and less charge recombination, as seen from the electrochemical impedance spectroscopy data. This study not only demonstrates the excellent power-conversion efficiency of new fused-thiophene ruthenium sensitizers, but also points to the promise that fused-thiophene antennas might be a useful molecule in the engineering of ruthenium dyes for DSSCs. [ABSTRACT FROM AUTHOR]

Abstract: Four donor–conjugated spacer–acceptor (D–π–A) organic dyes containing cyclopentadithiophene unit as a part of the conjugated spacer are prepared and studied to investigate the effects of the conjugated spacer and donor on the short-circuit current and conversion efficiency of the corresponding DSSCs. Theoretical calculations reveal that a shorter conjugated spacer or a stronger donor leads to more effective electron injection upon photo excitation. Therefore, D–π–A typed dye with longer conjugated spacer may have higher absorption coefficient and longer λ max. Nevertheless, it may also have lower effective electron injection upon photo excitation. Calculation data also show that cyclopentadithiophene although is a good moiety for extending the conjugation length of the organic dyes, it also acts as an electron sink, decreasing the effective electron injection. The transition probability calculated with the electron density difference analyses combining with the experimental absorption and photovoltaic performance data provides a useful protocol for designing organic photosensitizers for DSSCs at the electronic and structural levels. [Copyright &y& Elsevier]

Three unsymmetrical squaraines, where the electron-rich thiophene or bithiophene conjugated fragment was used to link unconventionally the squaraine core and carbazole (or methyl) group, were prepared. JYL-SQ1 with thiophene as a donor and indoline-carboxylic acid as an acceptor has λmax of 568 nm which is much longer than the general metal-free organic dyes. Adding a carbazole unit in JYL-SQ1 (forms JYL-SQ2) can red-shift the λmax to 603 nm. However, cabazole is not a strong donor (and indoline-carboxylic acid is a weak acceptor) the LUMO of all three dyes are delocalized majorly on squaraine unit: the excited electrons of dye molecules injecting into TiO2 are not so efficiency, resulting in low short-circuit current and conversion efficiency. The corresponding DSSC devices have the conversion efficiency of 0.71%, 2.59% and 2.22% for JYL-SQ1, JYL-SQ2 and THL-SQ3, respectively. [ABSTRACT FROM AUTHOR]

Seven new donor-spacer-acceptor metal-free organic dyes containing a fluorene and/or thiophene unit as a conjugated spacer are prepared and their physicochemical properties as well as photovoltaic performance are studied. The electron transfer from donor to acceptor upon excitation of these dyes is sensitive to the conjugated spacers. If a stronger donor moiety such as (ethylenedioxy)thiophene is used as a spacer, such as in F-E1 dye, the dye molecule has a better charge separation and therefore high efficiency. Furthermore, for the same donor and acceptor, fluorene is a better conjugated spacer than the bithiophene moiety because of its nonplanar conformation, which avoids the electron-hole recombination of dye upon photoexcitation. Short molecules with planar conformation aggregate easily, and the corresponding device reveals low open-circuit voltage Voc. On the other hand, dye molecules with long alkyl side chains (large size) adsorb less on the TiO2 electrode, which results in a smaller short-circuit current density Jsc. The difference in the efficiency of these dyes is small except for F-1 (owing to its short conjugation length), and electron density difference map analyses reveal that photoexcitation transfer of electron density from the donating moieties toward the acceptor/anchoring units occurs for all molecules. The small difference in the efficiency is attributed partly to the degree of effective charge transfer upon excitation, not totally to the absorption profile of the dye molecules. Furthermore, time-dependent DFT simulated absorption spectra are in excellent agreement with experimental spectra when the dyes are in their protonated states in THF solution. The transition probability calculated with the electron density difference analyses combined with the absorption data and photovoltaic performance provide useful information for designing organic sensitizers for dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

Abstract: A series of conjugated/non-conjugated copolymers and their corresponding oligomers were prepared and their optical and physical properties were investigated for understanding the merit of blocking the conjugated chromophores with non-conjugated spacers. It was found that compared to the oligomers, copolymers have the advantages of amorphous nature, high thermal stability, and good thin film processability without sacrificing the quantum efficiency and purity of the emission color. Furthermore, based on the optical data of these copolymers and oligomers, the conjugation length of the polyoctylthiophene was estimated to be extended over 23–31 octylthiophene rings. [Copyright &y& Elsevier]

Abstract: Starting from 2,6-bis-(3-octylthiophene-2yl)-pyridine, two new poly(alkylthiophene) derivatives, POTPyOT and POTPy, containing pyridine in the backbone were prepared from nickel(0)-mediated Stille coupling or by palladium-catalyzed Yamamoto coupling. These polymers exhibited good solubility in common organic solvents, thermal stability up to 400°C, and facile film formation. They were amorphous and give strong luminescence both in CHCl3 solution and solid state film. The polymers emitted blue light in solution with photoluminescence (PL) emission maximum at 420–484nm and green light with PL emission maximum at 500–514nm in thin films. These polymers showed a reversible redox reaction at potential from 0 to 1.3V (vs. SCE). Nevertheless, the reduced form of the polymer was very unstable; it decomposed in the presence of oxygen or water. The emission and UV–vis absorption of the polymer were influenced by the solvent polarity, protonation, and acid–base treatment. These may be the results of the stabilization of the polar excited state by solvation and the change of the conformation in polymer backbone. Electroluminescence (EL) was achieved from a single-layer PLED with the configuration of ITO/POTPyOT/Al. The turn-on voltage of the device is 10V and the λ max (550nm) of the EL is voltage independent. [Copyright &y& Elsevier]

Water-soluble conducting poly(2-(3thienyloxy)ethanesulfonic acid) (PTOESA)/V2O5 nanocomposite, (PTOESA)xV2O5, was prepared by simply mixing PTOESA with V2O5 wet gel at room temperature. XRD data showed that the interlayer spacings of (PTOESA)xV2O5 films are 14.0±1.5 Å and increased as the polymer content increased. These values are consistent with the insertion of polythiophene chains into the V2O5 layer gallery. The formation of alternative layers of PTOESA and V2O5 was further supported by depth profile SIMS analyses. Cyclic voltammograms of (PTOESA)xV2O5 film showed two pairs of redox peaks with colors varying from orange, yellowish green, green, to purple blue, depending on the stoichiometry of the nanocomposites. Moreover, a synergetic effect was observed on the electrochromic properties of these nanocomposites. It was found that the optical contrast (ΔOD) of the composites is better than those of PTOESA and V2O5 at the film thickness from 150 to 500 nm. The oxidation optical response time of (PTOESA)xV2O5 is independent of the stoichiometry and falls in between those of PTOESA and V2O5. At higher polymer content (x>0.5), the reduction optical response time of (PTOESA)xV2O5 is smaller than those of PTOESA and V2O5. Variable temperature conductivity data showed that the conductivity of (PTOESA)xV2O5 films increased as temperature increased, characteristic of thermal activated behavior, which was dominated by the interparticle contact resistance. The room-temperature conductivity of water-soluble (PTOESA)xV2O5 films was in between those of PTOESA and V2O5 xerogel and higher conductivity was found in the composite with lower polymer content. The anomalous conductivity of (PTOESA)xV2O5 with high PTOESA content may be due to the reason that the higher the polymer content, the bigger the grain size of (PTOESA)xV2O5 film as revealed with scanning electron microscopy and AFM micrographs. [Copyright &y& Elsevier]

From light to electricity: The inside cover picture illustrates the concept of designing hole transporting materials (HTMs) for perovskite solar cells. A subtle change of the central π‐bridge unit can lead to a significant improvement of device performance. In view of their excellent performance, the materials with two‐dimensional structural framework are promising HTMs for efficient and stable perovskite photovoltaic devices. More details can be found in the Full Paper by Yan‐Duo Lin et al. on page 307 in Issue 2, 2019 (10.1002/ente.201800939). [ABSTRACT FROM AUTHOR]

The open-circuit voltage of CH 3 NH 3 PbI 3 based photovoltaics was enhanced from 0.77 V to 0.9 V, which resulted in an improvement of the average power conversion efficiency from 5.63% to 11.74% achieved by tuning the work function of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer. The higher work function of the PEDOT:PSS (1:20 wt%) thin film, as compared to the PEDOT:PSS (1:6 wt%) and PEDOT:PSS (1:2.5 wt%) thin films, was observed using photoelectron spectrometer. The carrier density of PEDOT was obtained by analyzing the transmittance spectrum of PEDOT:PSS/glass with the transfer matrix method. The Drude model can be used to explain the increased work function of the PEDOT:PSS thin film obtained by decreasing the ratio of PEDOT to PSS. The increased carrier density of the PEDOT in PEDOT:PSS thin films originated from conformational changes in the PEDOT chains as confirmed by Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

Two new unsymmetrical squaraines (WCH-SQ10and WCH-SQ11), wherein the electron-rich 3,4-ethylenedioxy-thiophene conjugated fragment was linked unconventionally to the squaraine core and triphenyl amine donor, and carboxylic acid substituted quinoline was used as an acceptor, were prepared. WCH-SQ10and WCH-SQ11dyes in ethanol have the λmaxof 686 and 673 nm, respectively. The corresponding photovoltaic devices exhibit an attractively panchromatic response over 1000 nm, suggesting that quinoline benefits the low energetic electron injection. [ABSTRACT FROM AUTHOR]

Abstract: A novel, heteroleptic ruthenium dye comprising a vinyl group between the carboxylate and bipyridine segments as well as extended π-conjugation of the ancillary ligand, employing alkyl-bithiophene, was synthesized. The dye displayed a remarkably high absorption coefficient of 2.51 × 104 M−1 cm−1 (at 562 nm) for its metal-to-ligand charge transfer band. The photo-to-current conversion efficiency of the corresponding dye-sensitized solar cell was 9.12% under AM 1.5 (100 mW/cm2) irradiation. Furthermore, owing to both the very strong metal-to-ligand charge transfer band and the large number of dye molecules adsorbed on the TiO2 electrode, the conversion efficiency of the dye-sensitized cell was >7.5% at a light intensity ≤198 mW cm−2. [Copyright &y& Elsevier]