Bicyclopentadithiophene-Based Organic Semiconductor for Stable and High-Performance Perovskite Solar Cells Exceeding 22.

Well-performing organic-inorganic halide perovskites are susceptible to poor efficiency and instability due to their various defects at the interphases, grain boundaries (GBs), and surfaces. In this study, an in situ method is utilized for effectively passivating the under-coordinated Pb2+ defects of perovskite with new non-fullerene acceptors (NFAs) (INXBCDT; X = H, Cl, and Br) through their carbonyl and cyano functional groups during the antisolvent dripping process. It reveals that the bicyclopentadithiophene (BCDT) core with highly electron-withdrawing end-capping groups passivates GBs and boosts perovskite grain growth. This effective defect passivation decreases the trap density to increase the carrier recombination lifetime of the perovskite film. As a result, bromo-substituted dicyanomethylene indanone (INBr)-end-capped BCDT (INBrBCDT-b8; 3a)-passivated devices exhibit the highest power conversion efficiency (PCE) of 22.20% (vs those of 18.09% obtained for perovskite films without passivation) upon an optimized film preparation process. Note that devices treated with more soluble 2-ethylhexyl-substituted compounds (1a, 2a, and 3a) exhibit higher PCE than those treated with less soluble octyl-substituted compounds (1b, 2b, and 3b). It is also worth noting that BCDT is a cost-effective six-ring core that is easier to synthesize with a higher yield and therefore much cheaper than those with highly fused-ring cores. In addition, a long-term stability test in a glovebox for 1500 h reveals that the perovskite solar cells (PSCs) based on a perovskite absorber treated with compound 3a maintain ∼90% of their initial PCE. This is the first example of the simplest high-conjugation additive for perovskite film to achieve a PCE greater than 22% of the corresponding lead-based PSCs.

Diselenophene-Dithioalkylthiophene Based Quinoidal Small Molecules for Ambipolar Organic Field Effect Transistors.

This work presents a series of novel quinoidal organic semiconductors based on diselenophene-dithioalkylthiophene (DSpDST) conjugated cores with various side-chain lengths (-thiohexyl, -thiodecyl, and -thiotetradecyl, designated DSpDSTQ-6, DSpDSTQ-10, and DSpDSTQ-14, respectively). The purpose of this research is to develop solution-processable organic semiconductors using dicyanomethylene end-capped organic small molecules for organic field effect transistors (OFETs) application. The physical, electrochemical, and electrical properties of these new DSpDSTQs are systematically studied, along with their performance in OFETs and thin film morphologies. Additionally, the molecular structures of DSpDSTQ are determined through density functional theory (DFT) calculations and single-crystal X-ray diffraction analysis. The results reveal the presence of intramolecular S (alkyl)···Se (selenophene) interactions, which result in a planar SR-containing DSpDSTQ core, thereby promoting extended π-orbital interactions and efficient charge transport in the OFETs. Moreover, the influence of thioalkyl side chain length on surface morphologies and microstructures is investigated. Remarkably, the compound with the shortest thioalkyl chain, DSpDSTQ-6, demonstrates ambipolar carrier transport with the highest electron and hole mobilities of 0.334 and 0.463 cm2 V-1 s-1 , respectively. These findings highlight the excellence of ambipolar characteristics of solution-processable OFETs based on DSpDSTQs even under ambient conditions.

Dopant-Free Pyrrolopyrrole-Based (PPr) Polymeric Hole-Transporting Materials for Efficient Tin-Based Perovskite Solar Cells with Stability Over 6000 h.

A new set of pyrrolopyrrole-based (PPr) polymers incorporated with thioalkylated/alkylated bithiophene (SBT/BT) is synthesized and explored as hole-transporting materials (HTMs) for Sn-based perovskite solar cells (TPSCs). Three bithiophenyl spacers bearing the thioalkylated hexyl (SBT-6), thioalkylated tetradecyl (SBT-14), and tetradecyl (BT-14) chains are utilized to examine the effect of the alkyl chain lengths. Among them, the TPSCs are fabricated using PPr-SBT-14 as HTMs through a two-step approach by attaining a power conversion efficiency (PCE) of 7.6% with a remarkable long-term stability beyond 6000 h, which has not been reported elsewhere for a non-PEDOT:PSS-based TPSC. The PPr-SBT-14 device is stable under light irradiation for 5 h in air (50% relative humidity) at the maximum power point (MPP). The highly planar structure, strong intramolecular S(alkyl)···S(thiophene) interactions, and extended π-conjugation of SBT enable the PPr-SBT-14 device to outperform the standard poly(3-hexylthiophene,-2,5-diyl (P3HT) and other devices. The longer thio-tetradecyl chain in SBT-14 restricts molecular rotation and strongly affects the molecular conformation, solubility, and film wettability over other polymers. Thus, the present study makes a promising dopant-free polymeric HTM model for the future design of highly efficient and stable TPSCs.

Triarylamine-Functionalized Imidazolyl-Capped Bithiophene Hole Transporting Material for Cost-Effective Perovskite Solar Cells.

Triarylamine end-capped-functionalized arylene-imidazole derivatives were synthesized from readily accessible, inexpensive precursors and employed as hole transporting materials (HTMs) in perovskite solar cells (PSCs). All the HTMs displayed high thermal decomposition temperatures (>410 °C), which is beneficial for realizing stable PSC devices. In addition, the new HTMs show appropriate energy level alignment with the perovskite layer, ensuring efficient hole transfer from perovskites to HTMs. Interestingly, PSCs fabricated with the triarylamine-functionalized imidazolyl-capped bithiophene molecule (DImBT-4D) as the HTM exhibited the best power conversion efficiency of 20.11%, comparable to that of the benchmark HTM spiro-OMeTAD, prompting it be a prospective candidate for large-scale PSC applications.

Photoelectric effect of hybrid ultraviolet-sensitized phototransistors from an n-type organic semiconductor and an all-inorganic perovskite quantum dot photosensitizer.

Low-dimensional all-inorganic perovskite quantum dots (QDs) have been increasingly developed as photo-sensing materials in the field of photodetectors because of their strong light-absorption capability and broad bandgap tunability. Here, solution-processed hybrid phototransistors built by a dithienothiophenoquinoid (DTTQ) n-type organic semiconductor transport channel mixing with a colloidal CsPbBr3 perovskite QD photosensitizer are demonstrated by manipulating the relative volume ratio from 10 : 0 to 9 : 1, 7 : 3, 5 : 5, 3 : 7, 1 : 9, and 0 : 10. This results in a significantly enhanced photodetection performance owing to the advantages of a high UV absorption cross-section based on the perovskite QDs, efficient carrier transport abilities from the DTTQ semiconductor, and the photogating effect between the bulk heterojunction photocarrier transfer interfaces. The optimized DTTQ : QD (3 : 7) hybrid phototransistor achieves a high photoresponsivity (R) of 7.1 × 105 A W-1, a photosensitivity (S) of 1.8 × 104, and a photodetectivity (D) of 3.6 × 1013 Jones at 365 nm. Such a solution-based fabrication process using a hybrid approach directly integrated into a sensitized phototransistor potentially holds promising photoelectric applications towards advanced light-stimulated photodetection.

Controlled Synthesis of Poly[(3-alkylthio)thiophene]s and Their Application to Organic Field-Effect Transistors.

Regioregular polythiophenes have been widely used in organic electronic applications due to their solution processability with chemical modification through side chain engineering, as well as their microstructural organization and good hole transport properties. Here, we introduce alkylthio side chains, (poly[(3-alkylthio)thiophene]s; P3ATTs), with strong noncovalent sulfur molecular interactions, to main chain thienyl backbones. These P3ATTs were compared with alkyl-substituted polythiophene (poly(3-alkylthiophene); P3AT) variants such that the effects of straight (hexyl and decyl) and branched (2-ethylhexyl) side chains (with and without S atoms) on their thin-film morphologies and crystalline states could be investigated. P3ATTs with linear alkylthio side chains (P3HTT, hexylthio; P3DTT, decylthio) did not attain the expected higher organic field-effect transistor (OFET) mobilities with respect to P3HT (hexyl) and P3DT (decyl) mainly due to their lower regioregularity (76-78%), although P3ATTs exhibit an enhanced tendency for aggregation and compact molecular packing, as indicated by the red-shifting of the absorption spectra and the shortening of the π-π stacking distance, respectively. Moreover, the loss of regioregularity issue can be solved by introducing more soluble 2-ethylhexylthio branched side chains to form poly[3-(2-ethylhexylthio)thiophene] (P3EHTT), which provides enhanced crystallinity and efficient charge mobility (increased by up to a factor of 3) with respect to the poly(2-ethylhexylthiophene) (P3EHT) without S atoms in the side moieties. This study demonstrates that the presence of side chain alkylthio structural motifs with nonbonded interactions in polythiophene semiconductors has a beneficial impact on the molecular conformation, morphologies, structural packing, and charge transport in OFET devices.

Stable Perovskite Solar Cells Using Molecularly Engineered Functionalized Oligothiophenes as Low-Cost Hole-Transporting Materials.

Triarylamine-substituted bithiophene (BT-4D), terthiophene (TT-4D), and quarterthiophene (QT-4D) small molecules are synthesized and used as low-cost hole-transporting materials (HTMs) for perovskite solar cells (PSCs). The optoelectronic, electrochemical, and thermal properties of the compounds are investigated systematically. The BT-4D, TT-4D, and QT-4D compounds exhibit thermal decomposition temperature over 400 °C. The n-i-p configured perovskite solar cells (PSCs) fabricated with BT-4D as HTM show the maximum power conversion efficiency (PCE) of 19.34% owing to its better hole-extracting properties and film formation compared to TT-4D and QT-4D, which exhibit PCE of 17% and 16%, respectively. Importantly, PSCs using BT-4D demonstrate exceptional stability by retaining 98% of its initial PCE after 1186 h of continuous 1 sun illumination. The remarkable long-term stability and facile synthetic procedure of BT-4D show a great promise for efficient, stable, and low-cost HTMs for PSCs for commercial applications.

A Solution Processable Dithioalkyl Dithienothiophene (DSDTT) Based Small Molecule and Its Blends for High Performance Organic Field Effect Transistors.

The 3,5-dithiooctyl dithienothiophene based small molecular semiconductor DDTT-DSDTT (1), end functionalized with fused dithienothiophene (DTT) units, was synthesized and characterized for organic field effect transistors (OFET). The thermal, optical, electrochemical, and computed electronic structural properties of 1 were investigated and contrasted. The single crystal structure of 1 reveals the presence of intramolecular locks between S(alkyl)···S(thiophene), with a very short S-S distance of 3.10 Å, and a planar core. When measured in an OFET device compound 1 exhibits a hole mobility of 3.19 cm2 V-1 s-1, when the semiconductor layer is processed by a solution-shearing deposition method and using environmentally acceptable anisole as the solvent. This is the highest value reported to date for an all-thiophene based molecular semiconductor. In addition, solution-processed small molecule/insulating polymer (1/PαMS) blend films and devices were investigated. Morphological analysis reveals a nanoscopic vertical phase separation with the PαMS layer preferentially contacting the dielectric and 1 located on top of the stack. The OFET based on the blend comprising 50% weight of 1 exhibits a hole mobility of 2.44 cm2 V-1 s-1 and a very smaller threshold voltage shift under gate bias stress.

Solution-Processable Quinoidal Dithioalkylterthiophene-Based Small Molecules Pseudo-Pentathienoacenes via an Intramolecular S···S Lock for High-Performance n-Type Organic Field-Effect Transistors.

A new organic small-molecule family comprising tetracyanoquinodimethane-substituted quinoidal dithioalky(SR)terthiophenes (DSTQs) (DSTQ-6 (1); SR = SC6H13, DSTQ-10 (2); SR = SC10H21, DSTQ-14 (3); SR = SC10H21) was synthesized and contrasted with a nonthioalkylated analogue (DRTQ-14 (4); R = C14H29). The physical, electrochemical, and electrical properties of these new compounds are thoroughly investigated. Optimized geometries obtained from density functional theory calculations and single-crystal X-ray diffraction reveal the planarity of the SR-containing DSTQ core. DSTQs pack in a slipped π-π stacked two-dimensional arrangement, with a short intermolecular stacking distance of 3.55 Å and short intermolecular S···N contacts of 3.56 Å. Thin-film morphological analysis by grazing incident X-ray diffraction reveals that all DSTQ molecules are packed in an edge-on fashion on the substrate. The favorable molecular packing, the high core planarity, and very low lowest unoccupied molecular orbital (LUMO) energy level (-4.2 eV) suggest that DSTQs could be electron-transporting semiconductors. Organic field-effect transistors based on solution-sheared DSTQ-14 exhibit the highest electron mobility of 0.77 cm2 V-1 s-1 with good ambient stability, which is the highest value reported to date for such a solution process terthiophene-based small molecular semiconductor. These results demonstrate that the device performance of solution-sheared DSTQs can be improved by side chain engineering.

Thioalkyl-Functionalized Bithiophene (SBT)-Based Organic Sensitizers for High-Performance Dye-Sensitized Solar Cells.

A series of 3,3'-dithioalkyl-2,2'-bithiophene (SBT)-based organic chromophores were designed and developed for the use in dye-sensitized solar cells (DSSCs). By appropriate structural modification of the SBT π-linkers with different alkyl chains and conjugated thiophene units, chromophore aggregation and interfacial charge recombination could be suppressed to a remarkable degree. Single-crystal and optical/electrochemical data clearly show that the SBT core is nearly planar with the torsional angle <1°, likely via S(alkyl)···S(thiophene) intramolecular locks. Therefore, this highly π-conjugated unit should enhance panchromatic light-harvesting and prove to be an excellent core for organic dye. For comparison, the 3,3'-dialkyl-2,2'-bithiophene (BT)-based dye was also prepared. Under 1 sun (100 mW cm-2) illumination, an optimized SBT-6 dye-sensitized cell indicates a short-circuit current density (JSC) of 17.21 mA cm-2, an open-circuit voltage (VOC) of 0.78 V, and a fill factor (FF) of 0.71, corresponding to a power conversion efficiency (η) of 9.47%, which is nearly two times higher than that of alkylated bithiophene (BT)-based chromophores. Finally, the proposed sensitizer SBT-6 exhibited an excellent η of 23.57% under the T5 fluorescent illumination of 6000 lux. To the best of our knowledge, this is the highest power conversion efficiencies (PCE) value reported to date among the studied thiophene or bithiophene-based chromophores.

Thienoisoindigo (TII)-Based Quinoidal Small Molecules for High-Performance n-Type Organic Field Effect Transistors.

A novel quinoidal thienoisoindigo (TII)-containing small molecule family with dicyanomethylene end-capping units and various alkyl chains is synthesized as n-type organic small molecules for solution-processable organic field effect transistors (OFETs). The molecular structure of the 2-hexyldecyl substituted derivative, TIIQ-b16, is determined via single-crystal X-ray diffraction and shows that the TIIQ core is planar and exhibits molecular layers stacked in a "face-to-face" arrangement with short core intermolecular distances of 3.28 Å. The very planar core structure, shortest intermolecular N···H distance (2.52 Å), existence of an intramolecular non-bonded contact between sulfur and oxygen atom (S···O) of 2.80 Å, and a very low-lying LUMO energy level of -4.16 eV suggest that TIIQ molecules should be electron transporting semiconductors. The physical, thermal, and electrochemical properties as well as OFET performance and thin film morphologies of these new TIIQs are systematically studied. Thus, air-processed TIIQ-b16 OFETs exhibit an electron mobility up to 2.54 cm2 V-1 s-1 with a current ON/OFF ratio of 105-106, which is the first demonstration of TII-based small molecules exhibiting unipolar electron transport characteristics and enhanced ambient stability. These results indicate that construction of quinoidal molecule from TII moiety is a successful approach to enhance n-type charge transport characteristics.

Potential-selective fate of 2D chiral crystallization on an electrode surface.

Molecular resolution STM is used to study the spatial structure and chirality of adsorbed Δ4,4-dicyclopenta[2,1-b:3,4-b]-dithiophene (TTE) on an Au(111) electrode, revealing an ordered, racemate adlayer made of homogeneously mixed R- and S-TTE on the (1 × 1) substrate and patches of R- or S-only TTE on the reconstructed Au(111) at more and less positive potentials.

Cs2SnI6-Encapsulated Multidye-Sensitized All-Solid-State Solar Cells.

The design of a dye-sensitized solar cell (DSSC) based on the simultaneous incorporation of multiple dyes is examined. By investigating the use of the porphyrin-based YD2-o-C8 and YDD6, and the organic chromophore TTAR, which can act as complementary absorbers, we are able to enhance the capture of incoming light across the solar spectrum. This is demonstrated first by using a conventional DSSC architecture with a liquid electrolyte and performed a power conversion efficiency (PCE) of 11.2%, representing an improvement over cells based on each of the independent dyes. Next, we used Cs2SnI6 as an encapsulating layer over the sensitizing molecules to reduce charge leakage across the dye layers and also added to the absorption of longer wavelengths up to one micron. Finally, we fabricated a cell utilizing a Cs2SnI6/succinonitrile solid hole-transport electrolyte and achieved a PCE of ∼8.5%. It is expected that the all solid-state design will go a long way toward improving long-term device stability.

Solution properties of imidazolium-based amphiphilic polyelectrolyte in pure- and mixed-solvent media.

The solution properties of a synthesized imidazolium-based amphiphilic polyelectrolyte dissolved in pure- and mixed-solvent media composed of two aprotic polar solvents (N,N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP)) having a similar dielectric constant are explored in the semidilute regime (1-4 wt%). Rheological characterizations reveal that the use of mixed-solvent media (e.g., DMAc/NMP with 1 : 1 in volume fraction, designated as 1 : 1 DMAc/NMP) leads to a substantial reduction in the solution viscosity while altering the fluid attribute from gel-like (G' > G'') to critical-gel-like (G' ∼ G'' ∼ ωn, with n ≅ 0.5). To gain insight into these peculiar rheological features, dynamic light scattering analysis of the representative 1 : 1 DMAc/NMP medium indicates that the fraction and mean hydrodynamic radius of the micrometer-sized cluster alter substantially, too. Multiscale static light/X-ray scattering characterizations further reveal that only the NMP and 1 : 1 DMAc/NMP media (and not the DMAc) are capable of producing hierarchical structures of the cluster interior that are beneficial to mesoscale ion conduction, as supported by ac conductivity measurements. Overall, the present findings suggest that an appropriate selection of mixed-solvent media may offer an exceptional opportunity to promote the rheological, structural, and ion-conduction properties of a polyelectrolyte solution beyond the reach of the corresponding pure-solvent media.

Dopant-Free Tetrakis-Triphenylamine Hole Transporting Material for Efficient Tin-Based Perovskite Solar Cells.

Developing dopant-free hole transporting layers (HTLs) is critical in achieving high-performance and robust state-of-the-art perovskite photovoltaics, especially for the air-sensitive tin-based perovskite systems. The commonly used HTLs require hygroscopic dopants and additives for optimal performance, which adds extra cost to manufacturing and limits long-term device stability. Here we demonstrate the use of a novel tetrakis-triphenylamine (TPE) small molecule prepared by a facile synthetic route as a superior dopant-free HTL for lead-free tin-based perovskite solar cells. The best-performing tin iodide perovskite cells employing the novel mixed-cation ethylenediammonium/formamidinium with the dopant-free TPE HTL achieve a power conversion efficiency as high as 7.23%, ascribed to the HTL's suitable band alignment and excellent hole extraction/collection properties. This efficiency is one of the highest reported so far for tin halide perovskite systems, highlighting potential application of TPE HTL material in low-cost high-performance tin-based perovskite solar cells.

Intramolecular Locked Dithioalkylbithiophene-Based Semiconductors for High-Performance Organic Field-Effect Transistors.

New 3,3'-dithioalkyl-2,2'-bithiophene (SBT)-based small molecular and polymeric semiconductors are synthesized by end-capping or copolymerization with dithienothiophen-2-yl units. Single-crystal, molecular orbital computations, and optical/electrochemical data indicate that the SBT core is completely planar, likely via S(alkyl)⋯S(thiophene) intramolecular locks. Therefore, compared to semiconductors based on the conventional 3,3'-dialkyl-2,2'-bithiophene, the resulting SBT systems are planar (torsional angle <1°) and highly π-conjugated. Charge transport is investigated for solution-sheared films in field-effect transistors demonstrating that SBT can enable good semiconducting materials with hole mobilities ranging from ≈0.03 to 1.7 cm2 V-1 s-1 . Transport difference within this family is rationalized by film morphology, as accessed by grazing incidence X-ray diffraction experiments.

High performance solution-processable tetrathienoacene (TTAR) based small molecules for organic field effect transistors (OFETs).

Three new organic semiconductors with alkyl chain-substituted tetrathienoacene (TTAR) as the central core and both ends capped with thiophene (DT-TTAR), thienothiophene (DTT-TTAR) and dithienothiophene (DDTT-TTAR) have been synthesized and characterized for organic field effect transistor (OFET) applications. A hole mobility of 0.81 cm2 V-1 s-1 was achieved for the DDTT-TTAR film, which represents the highest mobility yet found for a solution-processable p-type TTAR-based small molecular semiconductors.

Multifunctional Iodide-Free Polymeric Ionic Liquid for Quasi-Solid-State Dye-Sensitized Solar Cells with a High Open-Circuit Voltage.

A polymeric ionic liquid, poly(oxyethylene)-imide-imidazolium selenocyanate (POEI-IS), was newly synthesized and used for a multifunctional gel electrolyte in a quasi-solid-state dye-sensitized solar cell (QSS-DSSC). POEI-IS has several functions: (a) acts as a gelling agent for the electrolyte of the DSSC, (b) possesses a redox mediator of SeCN(-), which is aimed to form a SeCN(-)/(SeCN)3(-) redox couple with a more positive redox potential than that of traditional I(-)/I3(-), (c) chelates the potassium cations through the lone pair electrons of the oxygen atoms of its poly(oxyethylene)-imide-imidazolium (POEI-I) segments, and (d) obstructs the recombination of photoinjected electrons with (SeCN)3(-) ions in the electrolyte through its POEI-I segments. Thus, the POEI-IS renders a high open-circuit voltage (VOC) to the QSS-DSSC due to its functions of b-d and prolongs the stability of the cell due to its function of a. The QSS-DSSC with the gel electrolyte containing 30 wt % of the POEI-IS in liquid selenocyanate electrolyte exhibited a high VOC of 825.50 ± 3.51 mV and a high power conversion efficiency (η) of 8.18 ± 0.02%. The QSS-DSSC with 30 wt % POEI-IS retained up to 95% of its initial η after an at-rest stability test with the period of more than 1,000 h.

Synthesis and Characterization of Two-Photon Active Chromophores Based on Tetrathienoacene (TTA) and Dithienothiophene (DTT).

Three new donor-π-donor (D-π-D) tetrathienoacene (thieno[2',3':4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTA))-cored chromophores, end-functionalized with electron-donating triphenylamine (TPA) groups, were developed and characterized for their two-photon-related properties by using both nano- and femtosecond laser pulses as the probing tools. TTA-based chromophores exhibit stronger and more widely dispersed two-photon absorption (2PA) than those of dithienothiophene (DTT)-based congeners. As a consequence, the bithiophene-conjugated TTA chromophore exhibits the highest maximum 2PA cross-section value (up to 2500 GM) with good thermal stability, and thus, it is the best performing two-photon chromophore among the studied model compounds. The bithiophene-conjugated DTT analogue exhibits the second highest maximum two-photon absorptivity of 1950 GM, which is nearly 7 times larger than that of previously reported DTT-based chromophores.

Metal-free tetrathienoacene sensitizers for high-performance dye-sensitized solar cells.

A new series of metal-free organic chromophores (TPA-TTAR-A (1), TPA-T-TTAR-A (2), TPA-TTAR-T-A (3), and TPA-T-TTAR-T-A (4)) are synthesized for application in dye-sensitized solar cells (DSSC) based on a donor-π-bridge-acceptor (D-π-A) design. Here a simple triphenylamine (TPA) moiety serves as the electron donor, a cyanoacrylic acid as the electron acceptor and anchoring group, and a novel tetrathienoacene (TTA) as the π-bridge unit. Because of the extensively conjugated TTA π-bridge, these dyes exhibit high extinction coefficients (4.5-5.2 × 10(4) M(-1) cm(-1)). By strategically inserting a thiophene spacer on the donor or acceptor side of the molecules, the electronic structures of these TTA-based dyes can be readily tuned. Furthermore, addition of a thiophene spacer has a significant influence on the dye orientation and self-assembly modality on TiO2 surfaces. The insertion of a thiophene between the π-bridge and the cyanoacrylic acid anchoring group in TPA-TTAR-T-A (dye 3) promotes more vertical dye orientation and denser packing on TiO2 (molecular footprint = 79 Å(2)), thus enabling optimal dye loading. Using dye 3, a DSSC power conversion efficiency (PCE) of 10.1% with Voc = 0.833 V, Jsc = 16.5 mA/cm(2), and FF = 70.0% is achieved, among the highest reported to date for metal-free organic DSSC sensitizers using an I(-)/I3(-) redox shuttle. Photophysical measurements on dye-grafted TiO2 films reveal that the additional thiophene unit in dye 3 enhances the electron injection efficiency, in agreement with the high quantum efficiency.