Influence of the π‑Bridge-Fused Ring and Acceptor Unit Extension in D−π–A-Structured Organic Dyes for Highly Efficient Dye-Sensitized Solar Cells

Three new D−π–A-structured organic dyes, coded as SGT-138, SGT-150, and SGT-151, with the expansion of π-conjugation in the π-bridge and acceptor parts have been developed to adjust HOMO/LUMO levels and to expand the light absorption range of organic dyes. Referring to the SGT-137 dye, the π-bridge group was extended from the 4-hexyl-4H-thieno[3,2-b]indole (TI) to the 9-hexyl-9H-thieno[2′,3′:4,5]thieno[3,2-b]indole (TII), and the acceptor group was extended from (E)-3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylic acid (BTCA) to (E)-3-(4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)phenyl)-2-cyanoacrylic acid (BTECA), where TII was introduced as a π-bridging unit for the first time. It was determined that both extensions are promising strategies to enhance the light-harvesting ability. They present several features, such as (i) efficiently intensifying the extinction coefficient and expanding the absorption bands; (ii) exhibiting enhanced intramolecular charge transfer in comparison with the SGT-137; and (iii) being favorable to photoelectric current generation of dye-sensitized solar cells (DSSCs) with cobalt electrolytes. In particular, the π-spacer extension from TI to TII was useful for modulating the HOMO energy levels, while the acceptor extension from BTCA to BTECA was useful for modulating the LUMO energy levels. These phenomena could be explained with the aid of density functional theory calculations. Finally, the DSSCs based on new SGT-dyes with an HC-A1 co-adsorbent presented good power conversion efficiencies as high as 11.23, 11.30, 11.05, and 10.80% for SGT-137, SGT-138, SGT-150, and SGT-151, respectively. Furthermore, it was determined that the use of the bulky co-adsorbent, HC-A1, can effectively suppress the structural relaxation of dyes in the excited state, thereby enhancing the charge injection rate of SGT-dyes. The observations in time-resolved photoluminescence were indeed consistent with the variation in the PCE, quantitatively

Synergistic Effect of Size-Tailored Structural Engineering and Postinterface Modification for Highly Efficient and Stable Dye-Sensitized Solar Cells

Despite significant progress in device performance, dye-sensitized solar cells (DSSCs) continue to fall short of their theoretical potential. Moreover, research in recent years needs to pay more attention to improving the device fabrication process. To achieve the theoretical efficiency limit, it is crucial to optimize the interface between the dye and TiO2 nanoparticles in the entire device stack. Our study indicates that optimizing the structure or size of the coadsorbents and implementing a monolayer adsorption process can be an effective strategy to reduce charge recombination and enhance light-harvesting properties. Our research aims to develop a surface-coating adsorbent plan that controls the TiO2 nanoparticle interface to achieve the radiative limit of power conversion efficiency (PCE). Specifically, we utilized 2-thiophenecarboxylic acid (THCA) or chenodeoxycholic acid (CDCA) as postinterfacial surface-coating adsorbents. Our results demonstrate that this approach effectively achieves the desired PCE limit. Combined with the coadsorbent structure engineering and interface optimization, the device increased the packing area on the TiO2 nanoparticles’ surface, reaching an improved PCE of over 13.17% under simulated sunlight (1.5G), which is the highest efficiency of a porphyrin single dye-based DSSC. In particular, this practical approach was also applied to a large-area DSSC with an area of 3 cm2, yielding a remarkable PCE of 9.04%. Furthermore, when applied to a polymer gel electrolyte, this novel approach recorded the highest PCE of 11.16% with a long-term operational stability of up to 1000 h for the quasi-solid-state DSSCs. Our research findings provide a promising avenue for achieving high-performance DSSCs with ease of access and demonstrate practical applications as alternatives to conventional power sources

A Eu^III Tetrakis(β-diketonate) Dimeric Complex: Photophysical Properties, Structural Elucidation by Sparkle/AM1 Calculations, and Doping into PMMA Films and Nanowires

Reaction of Ln^III with a tetrakis­(diketone) ligand H₄L [1,1′-(4,4′-(2,2-bis­((4-(4,4,4-trifluoro-3-oxobutanoyl) phenoxy)­methyl)­propane-1,3-diyl)­bis­(oxy)­bis­(4,1-phenylene))­bis­(4,4,4-trifluorobutane-1,3-dione)] gives new podates which, according to mass spectral data and Sparkle/AM1 calculations, can be described as dimers, (NBu₄[LnL])₂ (Ln = Eu, Tb, Gd:Eu), in both solid-state and dimethylformamide (DMF) solution. The photophysical properties of the Eu^III podate are compared with those of the mononuclear diketonate (NBu₄[Eu­(BTFA)₄], BTFA = benzoyltrifluoroacetonate), the crystal structure of which is also reported. The new Eu^III dimeric complex displays bright red luminescence upon irradiation at the ligand-centered band in the range of 250–400 nm, irrespective of the medium. The emission quantum yields and the luminescence lifetimes of (NBu₄[EuL])₂ (solid state: 51% ± 8% and 710 ± 2 μs; DMF: 31% ± 5% and 717 ± 1 μs) at room temperature are comparable to those obtained for NBu₄[Eu­(BTFA)₄] (solid state: 60 ± 9% and 730 ± 5 μs; DMF: 30 ± 5% and 636 ± 1 μs). Sparkle/AM1 calculations were utilized for predicting the ground-state geometries of the Eu^III dimer. Theoretical Judd–Ofelt and photoluminescence parameters, including quantum yields, predicted from this model are in good agreement with the experimental values, proving the efficiency of this theoretical approach implemented in the LUMPAC software (http://lumpac.pro.br). The kinetic scheme for modeling energy transfer processes show that the main donor state is the ligand triplet state and that energy transfer occurs on both the ⁵D₁ (44.2%) and ⁵D₀ (55.8%) levels. Furthermore, the newly obtained Eu^III complex was doped into a PMMA matrix to form highly luminescent films and one-dimensional nanowires having emission quantum yield as high as 67%–69% (doping concentration = 4% by weight); these materials display bright red luminescence even under sunlight, so that interesting photonic applications can be foreseen

Novel Carbazole-Based Hole-Transporting Materials with Star-Shaped Chemical Structures for Perovskite-Sensitized Solar Cells

Novel carbazole-based hole-transporting materials (HTMs), including extended π-conjugated central core units such as 1,4-phenyl, 4,4′-biphenyl, or 1,3,5-trisphenylbenzene for promoting effective π–π stacking as well as the hexyloxy flexible group for enhancing solubility in organic solvent, have been synthesized as HTM of perovskite-sensitized solar cells. A HTM with 1,3,5-trisphenylbenzene core, coded as <b>SGT-411,</b> exhibited the highest charge conductivity caused by its intrinsic property to form crystallized structure. The perovskite-sensitized solar cells with <b>SGT-411</b> exhibited the highest PCE of 13.00%, which is 94% of that of the device derived from <i>spiro</i>-OMeTAD (13.76%). Time-resolved photoluminescence spectra indicate that <b>SGT-411</b> shows the shortest decay time constant, which is in agreement with the trends of conductivity data, indicating it having fastest charge regeneration. In this regard, a carbazole-based HTM with star-shaped chemical structure is considered to be a promising candidate HTM

B‑Doped Graphene as an Electrochemically Superior Metal-Free Cathode Material As Compared to Pt over a Co(II)/Co(III) Electrolyte for Dye-Sensitized Solar Cell

We report that B-doped graphene (BG) is prepared and tested as a counter electrode (CE) in dye-sensitized solar cells (DSSCs) in conjunction with Co­(bpy)₃^2+/3+ redox couple. The BG CE has a lower charge-transfer resistance and much higher electrochemical stability than those of Pt CE. As a result, the DSSC fabricated with BG CE exhibits superior power conversion efficiency to that of DSSC with Pt CE, suggesting potential to replace expensive Pt CE in DSSCs