Manman Fang

Triphenylamine derivatives: different molecular packing and the corresponding mechanoluminescent or mechanochromism property

Mechanoluminescence (ML), a fantastic phenomenon, has attracted increasing attention. However, to date, enumerable bright ML luminogens have been reported based on AIE building blocks. Herein, a new non-AIE unit of triphenylamine, for the first time, is utilized to construct a bright ML luminogen of TPA-1BA. Regardless of the similar molecular structure of TPA-1BA and its analogues TPA-2BA and TPA-3BA, totally different mechanoluminescent activities were observed. Through the careful analyses of their crystal structures, it is found that the non-centrosymmetric molecular arrangement and high lattice stability under mechanical stimulation should be mainly responsible for the ML property of TPA-1BA.

The introduction of conjugated isolation groups into the common acceptor cyanoacrylic acid: an efficient strategy to suppress the charge recombination in dye sensitized solar cells and the dramatically improved efficiency from 5.89% to 9.44%

The traditional acceptor, cyanoacrylic acid, was modified by the insertion of different aromatic rings as the isolation groups between the CN and COOH moieties, with the aim to suppress the possible charge recombination in dye sensitized solar cells. The results indicated that the larger isolation group was beneficial to inhibit the interfacial recombination, and the highest Voc was obtained by dye LI-78 with biphenyl as the isolation group. Combined with electron injection, the highest conversion efficiency (η) of 9.44% was achieved by dye LI-76 featuring a phenyl unit as the isolation group, whereas that of the reference sensitizer LI-75 without isolation group was only 5.89% under the same test conditions, providing a simple and convenient method to optimize the photovoltaic performance of organic dyes.

New D–π–A organic dyes containing a tert-butyl-capped indolo[3,2,1-jk]carbazole donor with bithiophene unit as π-linker for dye-sensitized solar cells

Two new D–π–A organic dyes containing a tert-butyl-capped indolo[3,2,1-jk]carbazole unit as a donor, bithiophene unit as a π-linker and cyanoacrylic acid as an acceptor (CL-10 and CL-11) have been designed and synthesized for dye-sensitized solar cells (DSSCs). By comparison, two dyes exhibit almost the same absorption and electrochemical properties, because the introduction of two hexyl groups at non-ortho β-positions of the 2,2′-bithiophene unit dose not destroy the planarity of the molecular skeleton of CL-11. However, the DSSC devices based on them show very different photovoltaic performances with power conversion efficiency (PCE) of 3.96% for CL-10 and 2.85% for CL-11, which can be attributed to the existence of the hexyl groups in CL-11 that lead to a big decrease of the dye adsorption onto TiO2. The addition of chenodeoxylic acid (CDCA) as a coadsorbant can significantly improve the photovoltaic performances of the DSSCs with a big increase in the PCE for CL-10 (4.68%) and CL-11 (4.66%).

Co-sensitization of “H”-type dyes with planar squaraine dyes for efficient dye-sensitized solar cells

Three “H”-type dyes with different linkage mode of two “D–π–A” moieties (LI-101, LI-102 and LI-103) were synthesized and applied to the co-sensitized system with the famous metal-free NIR squaraine dye of SQ2. Thanks to the advantage of the “H” configuration and their complementary spectra, the co-sensitized system exhibited the much improved photovoltaic performance of about a 70% enhancement, in comparison with that of SQ2 itself. Among them, the LI-102/SQ2 co-sensitized solar cell exhibited the highest conversion efficiency of 7.44% with 16.6 mA cm−2 for Jsc, 714 mV for Voc, 0.63 for FF.

Conjugated or Broken: The Introduction of Isolation Spacer ahead of the Anchoring Moiety and the Improved Device Performance

Acceptors in traditional dyes are generally designed closed to TiO2 substrate to form a strong electronic coupling with each other (e.g., cyanoacrylic acid) to enhance the electron injection for the high performance of the corresponding solar cells. However, some newly developed dyes with chromophores or main acceptors isolated from anchoring groups also exhibit comparable or even higher performances. To investigate the relatively untouched electronic coupling effect in dye-sensitized solar cells, a relatively precise method is proposed in which the strength is adjusted gradually by changing isolation spacers between main acceptors and anchoring groups to partially control the electronic interaction. After an analysis of 3 different groups of 11 sensitizers, it is inferred that the electronic coupling should be kept at a suitable level to balance the electron injection and recombination. Based on a reference dye LI-81 possessing a cyanoacrylic acid as acceptor and anchoring group, both photocurrent and photovoltage are synergistically improved after the properties of isolation spacers were changed through the adjustment of the length, steric hindrance, and push-pull electronic characteristic. Accordingly, the rationally designed dye LI-87 with an isolation spacer of thiophene ethylene gives an efficiency of 8.54% and further improved to 9.07% in the presence of CDCA, showing a new way to develop efficient sensitizers.

New anthracene-based organic dyes: the flexible position of the anthracene moiety bearing isolation groups in the conjugated bridge and the adjustable cell performance

Three organic sensitizers (LI-65–LI-67), featuring a 9,10-diarylsubstituted anthracene unit as part of the conjugated bridge, were designed and employed in dye-sensitized solar cells (DSCs). The two phenyl groups on the 9 and 10 positions of the anthracene ring acted as isolation groups, to suppress possible dye aggregation and electron recombination. With the flexible position of the isolation group in the conjugated bridge, interesting structure–property relationships were obtained: the isolation groups (the phenyl rings on the anthracene unit), close to the donor, were beneficial to the enhancement of the short circuit current (Jsc) values, with the highest Jsc value of 13.95 mA cm−2 (LI-65); once located in the middle of the π-bridge, the highest resistance of charge recombination and the longest electron lifetime were achieved and contributed to the enhanced open circuit voltage (Voc) of 722 mV, with the highest conversion efficiency (η) of 6.44% (LI-66, 25% higher than the lowest).

Significantly Improved Performance of Dye-Sensitized Solar Cell by Optimizing Organic Dyes with Pyrrole as the Isolation Space and Utilizing Alkyl Chain Engineering

The optimization of interfacial and intramolecular charge transfer of organic dyes is crucial to the photovoltaic performance of dye-sensitized solar cells. In this study, an efficient strategy was afforded by the introduction of alkylated pyrrole as the isolation spacer into organic dyes. The interfacial charge transfer can be organized by the tunable alkyl chains as a barrier layer to inhibit electron recombination, and the pull–push system can be strengthened by the incorporation of electron-withdrawing units (benzothiadiazole) and electron-rich moieties (pyrrole) into the conjugated bridge simultaneously, resulting in excellent light-harvesting capability. Therefore, the high conversion efficiency of 9.70% was achieved by LI-124 with suitable alkyl chains and device optimization.

Some new molecular design strategy to improve the performance of organic dyes in dye sensitized solar cells

With the aim to obtain good metal free organic dyes with high performance, different series of dyes were designed by optimizing their structures. Based on the experimental results, the relationship between the structure and property is summarized, to provide some useful information for the further development of new organic dyes.