Kihyung Song

High Molar Extinction Coefficient Organic Sensitizers for Efficient Dye-Sensitized Solar Cells

We have designed and synthesized highly efficient organic sensitizers with a planar thienothiophene-vinylene-thienothiophene linker. Under standard global AM 1.5 solar conditions, the JK-113-sensitized cell gave a short circuit photocurrent density (J(sc)) of 17.61 mA cm(-2), an open-circuit voltage (V(oc)) of 0.71 V, and a fill factor (FF) of 72%, corresponding to an overall conversion efficiency (eta) of 9.1%. The incident monochromatic photo-to-current conversion efficiency (IPCE) of JK-113 exceeds 80% over the spectral region from 400 to 640 nm, reaching its maximum of 93% at 475 nm. The band tails off toward 770 nm, contributing to the broad spectral light harvesting. Solar-cell devices based on the sensitizer JK-113 in conjunction with a volatile electrolyte and a solvent-free ionic liquid electrolyte gave high conversion efficiencies of 9.1% and 7.9%, respectively. The JK-113-based solar cell fabricated using a solvent-free ionic liquid electrolyte showed excellent stability under light soaking at 60 degrees C for 1000 h.

A polymer gel electrolyte to achieve ≥6% power conversion efficiency with a novel organic dye incorporating a low-band-gap chromophore

A quasi-solid-state dye-sensitized solar cell with novel organic sensitizers incorporating a benzothiadiazole chromophore showed excellent long-term stability, which exhibited 10% decrease during the 1000 h light soaking; the optimized cell gave a short circuit photocurrent density of 12.03 mA cm−2, an open circuit voltage of 0.720 V and a fill factor of 0.76, corresponding to an overall conversion efficiency of 6.61% under standard global AM 1.5 solar conditions.

Molecular engineering of organic sensitizers containing p-phenylene vinylene unit for dye-sensitized solar cells.

Three organic sensitizers containing bis-dimethylfluorenyl amino donor and a cyanoacrylic acid acceptor bridged by p-phenylene vinylene unit were synthesized. The power conversion efficiency was quite sensitive to the length of bridged phenylene vinylene groups. A nanocrystalline TiO2 dye-sensitized solar cell was fabricated using three sensitizers. The maximum power conversion efficiency of JK-59 reached 7.02%.

New type of organic sensitizers with a planar amine unit for efficient dye-sensitized solar cells.

A new type of organic sensitizers incorporating a planar amine unit have been synthesized and demonstrated to be a highly efficient sensitizers, showing evidence of lateral interactions on the TiO(2) surface. Under standard global air mass 1.5 solar conditions, the JK-98 sensitized cell gave a short circuit photocurrent density (J(sc)) of 16.78 mA cm(-2), an open-circuit voltage (V(oc)) of 0.745 V, and a fill factor (ff) of 0.70, corresponding to an overall conversion efficiency (η) of 8.71%.

Direct dynamics simulations

With todays improved computers, scientists can obtain the potential energy gradient for a classical trajectory by solving the time-independent Schrodinger equation at each numerical integration step. The practicality of this approach-called a direct dynamics simulation-is enhanced by its use of linear scaling and semiempirical electronic structure methods.

Molecular engineering of panchromatic unsymmetrical squaraines for dye-sensitized solar cell applications

Three unsymmetrical squaraine dyes JK-64, JK-65, and JK-64Hx, containing a bulky spirobifluorene or hexyloxyphenyl unit are designed and synthesized. These sensitizers, when anchored onto a TiO2 surface, exhibit decreased aggregation as well as enhanced unidirectional flow of electrons. Under standard global AM 1.5 solar conditions, an optimized JK-64Hx sensitized cell gave a short-circuit photocurrent density (Jsc) of 12.82 mA cm−2, an open-circuit voltage (Voc) of 0.54 V and a fill factor (ff) of 0.75, corresponding to an overall conversion efficiency (η) of 5.20%.

Molecular engineering of push-pull chromophore for efficient bulk-heterojunction morphology in solution processed small molecule organic photovoltaics

The synthesis and characterization of new push-pull chromophores, bisDMFA-diTh-CA, bisDMFA-diTh-MMN, and bisDMFA-diTh-MIMN from 5′-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)aniline (bisDMFA) electron donating, dithiophene bridging, and various electron withdrawing moieties, cyanoacrylic acid (CA), methylene malononitrile (MMN), and methylene indenylidene malononitrile (MIMN), were demonstrated for efficient solution processed BHJ solar cells. The photophysical properties, the hole mobilities from the space charge limitation of current (SCLC) J-V characteristics, and surface morphologies of these materials/PCBM bulk-heterojunction films were also investigated. The best power conversion efficiency of 3.66% (±0.12) with Jsc = 11.82 mA/cm2, FF = 0.35, and Voc = 0.90 V was observed in the BHJ film fabricated with the bisDMFA-diTh-MMN/C71-PCBM composite with 3% 1-chloronaphthalene (CN), which is an efficiency ∼82% and ∼49% higher than before and after post-annealing without treatment of CN, respectively.

Facile Synthesis of Fluorine‐Substituted Benzothiadiazole‐Based Organic Semiconductors and Their Use in Solution‐Processed Small‐Molecule Organic Solar Cells

A facile new protocol for the synthesis of iodinated derivatives of fluorinated benzothiadiazoles is demonstrated for the production of p-type semiconducting materials. The newly synthesized small-molecule compounds bis[TPA-diTh]-MonoF-BT and bis[TPA-diTh]-DiF-BT exhibited a power conversion efficiency of 2.95% and a high open-circuit voltage of 0.85 V in solution-processed small-molecule organic solar cells.

Post-transition state dynamics for propene ozonolysis : Intramolecular and unimolecular dynamics of molozonide

A direct chemical dynamics simulation, at the B3LYP6-31G(d) level of theory, was used to study the post-transition state intramolecular and unimolecular dynamics for the O3 + propene reaction. Comparisons of B3LYP6-31G(d) with CCSD(T)/cc-pVTZ and other levels of theory show that the former gives accurate structures and energies for the reactions stationary points. The direct dynamics simulations are initiated at the anti and syn O3 + propene transition states (TSs) and the TS symmetries are preserved in forming the molozonide intermediates. Anti<-->syn molozonide isomerization has a very low barrier of 2-3 kcalmol and its Rice-Ramsperger-Kassel-Marcus (RRKM) lifetime is 0.3 ps. However, the trajectory isomerization is slower and it is unclear whether this anti<-->syn equilibration is complete when the trajectories are terminated at 1.6 ps. The syn (anti) molozonides dissociate to CH3CHO + H2COO and H2CO + syn (anti) CH3CHOO. The kinetics for the latter reactions are in overall good agreement with RRKM theory, but there is a symmetry preserving non-RRKM dynamical constraint for the former. Dissociation of anti molozonide to CH3CHO + H2COO is enhanced and suppressed, respectively, for the trajectory ensembles initiated at the anti and syn O3 + propene TSs. The dissociation of syn molozonide to CH3CHO + H2COO may also be enhanced for trajectories initiated at the syn O3 + propene TS. At the time the trajectories are terminated at 1.6 ps, the ratio of the trajectory and RRKM values of the CH3CHO + H2COO product yield is 1.6 if the symmetries of the initiation and dissociation TSs are the same and 0.6 if their symmetries are different. There are coherences in the intramolecular energy flow, which depend on molozonides symmetry (i.e., anti or syn). This symmetry related dynamics is not completely understood, but it is clearly related to the non-RRKM dynamics for anti<-->syn isomerization and anti molozonide dissociation to CH3CHO + H2COO. Correlations are found between the stretching motions of molozonide, indicative of nonchaotic and non-RRKM dynamics. The non-RRKM dynamics of molozonide dissociation partitions vibration energy to H2COO that is larger than statistical partitioning. Though the direct dynamics simulations are classical, better agreement is obtained using quantum instead of classical harmonic RRKM theory. This may result from the neglect of anharmonicity in the RRKM calculations, the non-RRKM dynamics of the classical trajectories, or a combination of these two effects. The trajectories suggest that the equilibrium syn/anti molozonide ratio is approximately 1.1-1.2 times larger than that predicted by the harmonic densities of state, indicating an anharmonic correction.

Protonated Urea Collision-Induced Dissociation. Comparison of Experiments and Chemical Dynamics Simulations

Quantum mechanical plus molecular mechanical direct chemical dynamics were used, with electrospray tandem mass spectrometry experiments, potential energy surface calculations, and RRKM analyses, to study the gas-phase collision-induced dissociation (CID) of protonated urea. The direct dynamics were able to reproduce some of the experimental observations, in particular the presence of two fragmentation pathways, and, thus, to explain the dynamical origin of the two fragmentation ions observed in the CID spectra. A shattering dissociation mechanism takes place during the collision, and it becomes more important as the collision energy increases, thus explaining the linear increase of the high-energy reaction path (loss of ammonia) versus collision energy. By combining the different theoretical and experimental findings, a complete dynamical picture leading to the fragmentation was identified: (i) Oxygen-protonated urea, the most stable structure in the gas phase, must first isomerize to the nitrogen-protonated form. This can happen by multiple CID collisions or in the electrospray ionization process. (ii) Once the nitrogen-protonated isomer is formed, it can dissociate via two mechanisms: i.e, a slow, almost statistical, process forming a NH(4)(+)--NHCO intermediate that rapidly dissociates or a fast nonstatistical process which may lead to the high-energy products.