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Abstract The properties of three D1-π-D2-A dyes with dithiafulvenyl as donor (D1), phenothiazine as ancillary donor (D2), cyanoacrylic acid as acceptor along with different π groups, diphenyl for 1 , dithienyl for 2 , and thiopheneyl-benzothiadiazole for 3 , are studied. Besides the isolated dyes, the monomeric and dimeric adsorptions are also studied by combination of first principle and molecular dynamic simulations. There is no distinct difference among three dyes on the basis of only isolated dyes. When the dye-TiO 2 adsorption is considered, 3 is excluded because of its inferior items. However, it is still a difficult task to differentiate 1 and 2 even if the aggregation effect is included. The fluctuation of 1 is larger than that of 2 during the dynamic simulation resulting in the larger electronic coupling. The aggregation, especially for the aggregation during the dynamic simulation, is necessary to evaluate the performance of organic dye. Additionally, a new D-π-A dye 4 with the identical donor, π-bridge and acceptor is designed to compare with 2. 2 is totally superior to 4 indicating that suitable groups and appropriate configuration are both important to enhance the performance of organic dye. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Two new indoline-based D-A-π-A dyes, D3F and D3F2 (see Scheme 1), are developed on the basis of the reported D3 by insertion of one or two F atoms on benzothiadiazole group. Our central aim is to explore high-efficiency organic dyes applied in dye-sensitized solar cells by inclusion of a simple group rather than by employment of new complicated groups. The performance of two new designed organic dyes, D3F and D3F2 , is compared with that of D3 from various aspects including absorption spectrum, light harvesting efficiency, driving force, and open-circuit voltage. Besides the isolated dye, the interfacial property between dye and TiO 2 surface is studied. D3F and D3F2 do not show absolute superiority than D3 not only for the isolated dyes but also for the monomeric adsorption system. However, D3F and D3F2 would effectively reduce the influence of aggregation resulting in the much smaller intermolecular electronic coupling. Although the aggregation has attracted much attention recently, it is studied alone in most of studies. To comprehensively evaluate the performance of dye-sensitized solar cells, it is necessary to consider aggregation along with electron injection time from dye into TiO 2 rather than only static items, such as, band gap and absorption region. [ABSTRACT FROM AUTHOR]

Four A-D-A-D-A organic dyes with different auxiliary acceptor or donor groups have been theoretically investigated by first principle as potential photosensitizers in dye-sensitized solar cells. Judging from the isolated dyes, 2PZ-SP with diphenyl-substituted pyrido[3,4-b]pyrazine-2,5-thiophene as auxiliary acceptor is not suitable to be taken as organic dye in DSSCs because of the inappropriate electron density distribution. However, it is difficult to distinguish the performance of other three dyes since no one has all superiorities. After the dye is adsorbed on TiO 2 surface, the deviation between LUMO energy level of dye and conduction band of TiO 2 (101) surface is further enlarged, which is favorable for the electron injection. Moreover, 2PZ-PP stands out because of the smallest H-L energy gap and the shortest injection time. Finally, a new D-π-A dye with the identical donor, π group, and acceptor groups is designed to compare with 2PZ-BT . It is found that 2PZ-BT has the absolute advantage to be potential dye for DSSCs. Besides the suitable groups, the appropriate configuration is more critical aspect to determine the performance. [ABSTRACT FROM AUTHOR]

Thieno[3,4- c]pyrrole-4,6-dione-based organic sensitizers with triphenylamine ( FNE38 and FNE40) or julolidine ( FNE39 and FNE41) as electron-donating unit have been designed and synthesized. A linear hexyl group or a branched alkyl chain, the 2-ethylhexyl group, is incorporated into molecular skeleton of the dyes to minimize intermolecular interactions. The absorption, electrochemical, and photovoltaic properties for these sensitizers were then systematically investigated. It is found that the sensitizers have similar photophysical and electrochemical properties, such as absorption spectra and energy levels, owing to their close chemical structures. However, the quasi-solid-state dye-sensitized solar cells (DSSCs) based on the two types of sensitizers exhibit very different performance parameters. Upon the incorporation of the short ethyl group on the hexyl moiety, enhancements in both open-circuit voltage ( Voc) and short-circuit current ( Jsc) are achieved for the quasi-solid-state DSSCs. The Voc gains originating from the suppression of charge recombination were quantitatively investigated and are in good agreement with the experimentally observed Voc enhancements. Therefore, an enhanced solar energy conversion efficiency ( η) of 6.16 %, constituting an increase by 23 %, is achieved under standard AM 1.5 sunlight without the use of coadsorbant agents for the quasi-solid-state DSSC based on sensitizer FNE40, which bears the branched alkyl group, in comparison with that based on FNE38 carrying the linear alkyl group. This work presents a design concept for considering the crucial importance of the branched alkyl substituent in novel metal-free organic sensitizers. [ABSTRACT FROM AUTHOR]

Dye ‐ sensitized solar cells are regarded as a candidate for renewable energy source owing to their low cost, abundance of raw materials, ease of fabrication, and low energy consumption in the production process. In their Full Paper on page 168   ff., Gang Zhou, Zhong ‐ Sheng Wang et   al. introduced an ethyl group into a sensitizer with a linear hexyl group. With this branched 2 ‐ ethylhexyl group, the corresponding quasi ‐ solid ‐ state DSSC displayed a significantly reduced charge recombination rate, a longer electron lifetime, a higher photovoltage, and consequently an improved power conversion efficiency. [ABSTRACT FROM AUTHOR]

A series of carbazole-based organic dyes with asymmetric butterfly structure are designed and their efficiency is theoretically estimated. In the left “wing”, benzene and thiophene are employed as the π group. For respective left “wing”, three different right “wings” are constructed. The influence of nature and number of different π group on the efficiency is investigated. On the basis of the isolated dyes, the short-circuit current density ( J sc ), open-circuit voltage ( V oc ), and reorganization energy ( λ total ) are determined to evaluate the efficiency of the solar cell. Moreover, the structure of the dye adsorbed on the (TiO 2 ) 38 cluster is optimized by the first-principle. The adsorption energy and the density of states (DOS) are calculated to further estimate the efficiency. Combining all factors, the employment of two phenyl groups as π group of the right “wing” is favorable to improve the efficiency. [ABSTRACT FROM AUTHOR]

Four organic compounds with different π-linkers are theoretically explored as potential photosensitizers for application in dye-sensitized solar cells (DSSCs). Besides the isolated dyes, the interfacial properties of dyes adsorbed on TiO 2 anatase (101) surface are theoretically investigated. The overall conversion efficiency ( η ) of DSSCs is evaluated by the following items on the basis of the isolated dyes, including structures, absorption spectrum, energy gap, open-circuit voltage ( V oc ), short-circuit current density ( J sc ), and reorganization energies ( λ total ). After adsorbed on the TiO 2 surface, the electron would be efficiently injected from dye into the TiO 2 surface because of the increased of the lowest unoccupied molecular orbital (LUMO) energy level of the dyes, the decreased of the conduction band of TiO 2 surface, and the narrowed band gaps for both dye and TiO 2 . Moreover, the injection times are in a reasonable range indicating that they are ideal dyes. Combination of all items, the performance of THI-2T-C (See Scheme 1, the sketch structures of all the investigated isolated dyes) stands out from the rest investigated dyes from the theoretical viewpoint. Only enlargement of the π-linker extent is not a smart choice, since the nature of π-linker plays a more important role in affecting the performance of DSSCs. [ABSTRACT FROM AUTHOR]