Theoretical Studies of Optoelectronic Properties for Metal-free Sensitizers in DSSCs- Design Strategy for Improving Efficiency

• Main Authors: Chieh-Yu Tseng, 曾杰玉
• Other Authors: Jyh-Chiang Jiang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/13470727841322607674

碩士 === 國立臺灣科技大學 === 化學工程系 === 101 === Dye sensitized solar cells (DSSCs) have attracted considerable interest and been treated as promising alternative energy due to the high photon-to-current conversion efficiency, easy production and cost-effective properties. There are many efforts have been made to develop the efficient sensitizers, which are based on either metal or metal free organic complexes. But the lack of systematic and comprehensive developments results in little improvement in overall efficiency. In this contribution, we have designed a series of metal free dye-sensitizers and studied their optoelectronic properties using the DFT and TDDFT methods. The designed sensitizers are based on different combinations of electron -donating (D) and -withdrawing (A) units, incorporating a π-linker and an anchoring group to modify the electronic structures and tune the UV-Vis absorption. First, we considered oligomers composed by strong donor and strong acceptor to have higher degree of intra-molecular charge transfer. The calculations show acceptor plays more important role in optoelectronic properties of D-A systems and donor has minor influence which is able to change the overall spectra slightly. Therefore, we design the optoelectronic properties of metal-free sensitizers via changing the strength of acceptor. Then, MPBA-T-CDM*CN, MPBA-T-TP*CN and MPBA-T-CDT*CN are the most potential sensitizers we have already designed owing to their high molar extinction coefficients and absorption in 400~800 nm. In addition to analyzing the optoelectronic properties of designed sensitizers, we simulate the adsorption of promising sensitizers onto TiO¬¬2 semiconductor surface. Also, we use density of states analyses to discuss the electron coupling between surface and sensitizer. According to the calculation, all of the designed dyes reveal good electron coupling and electrons can efficiently inject to the TiO2 surface. In brief, the efficient sensitizers not only have appropriate optoelectronic properties but also can inject electrons to surface effectively. Therefore, we believe these sensitizers can improve the overall efficiency intensely.