Design Of Novel Zinc-Porphyrins Sensitizers And Investigation Of Factors Affecting The Photo-to-Electric Efficiency

A series of novel zinc-porphyrin sensitizers were designed in this work, parallel comparisons between electron-deficient pyrimidinyl and electron-rich phenyl were carried out. Equilibrium and electronic structures were calculated with density functional theory (DFT) and time dependent density functional theory method (TDDFT). Our calculated results suggest that the electron-deficient pyrimidinyl be more suitable as π-spacer in porphyrin sensitizers. Moreover, investigation of the role of varied-length π-spacer in the charge transfer and photo-to-electric efficiency was performed. We found that the dependence of electron transfer efficiency on the length is different for the electron-deficient pyrimidinyl and electron-rich phenyl, which differing in contribution to the power conversion efficiency.1. Franck-Condon simulation of vibrationally resolved optical spectra for Zinc complexes of phthalocyanine and tetrabenzoporphyrinInvestigations of electronic structural information of sensitizers would provide structural guidelines for molecular designs. Few theoretical investigations were performed to simulate the well-resolved spectra and assign the vibrational bands of the large molecules, on account of the difficulties to optimize the excited states and analyze a large number of final vibrational-normal modes. In the present work, the S0(?)S1optical spectra (that is, the Q band) of zinc complexes of phthalocyanine (ZnPc) and tetrabenzoporphyrin (ZnTBP) were simulated using time-dependent density functional theory (TDDFT) with the inclusions of Duschinsky and Herzberg-Teller contributions. The theoretical results provide a good description of the optical spectra and are proved to be in excellent agreement with experimental spectra in inert-gas matrices. This study focused attentions on the optical spectral contrasts and the nature of the electronic transitions in Q band region between ZnPc and ZnTBP. Simulation of high-resolved optical spectra would bridge the electronic and structural information, it would be important for us to design functional sensitizers2. Parallel comparison between the electron-deficient pyrimidinyl π-spacer and electron-rich phenyl π-spacer in the porphyrin sensitizersA mass of porphyrin sensitizers have been designed and synthesized for dye sensitized solar cells in previous works, almost all of them incorporated electron-rich system as π-spacer and adopted carboxylic acid as anchoring group. In this work, we firstly adopted the electron-deficient pyrimidine as an effective π-spacer and combined cyanoacrylic acid anchoring group. The photo-to-electric efficiencies of these sensitizers were qualitatively discussed from their light harvest efficiency, electron injection efficiency, charge collection efficiency and their regeneration efficiency. We found that the pyrimidinyl based sensitizer could yield a more bathochromic shift of the spectral absorption of the dye, and result in an improved spectral overlap with the solar spectrum and an enhanced light harvesting efficiency. Moreover, we found that not all electron transitions could make for the effective electron transfer from donor to acceptor groups, which means the porphyrin sensitizer performance in dye-sensitized solar cells not only relies on the extrinsic spectral absorption intensity, but also depends on the intrinsic character of electron movement related to electron excitation. Our calculated results can help us to find the relation between the structural information and photo-to-electric efficiency of sensitizers.3. Explore the Role of Varied-Length Pyrimidinyl and Phenyl Based Spacers in the Photo-to-Electric EfficiencyIncreasing the length of bridge can provide more space for structural modifications, and can also hinder the charge recombination process. For the electron-rich group based sensitizers, the calculated electron injection driving forces, the regeneration driving forces are gradually decreased with the distance of π-spacer increase. Though they can reap strong and red shift optical absorption, the charge transfer spatial distances are limited with the increase of spacer length. For the electron-deficient pyrimidinyl based sensitizers, the high electron injection efficiency, light harvest efficiency and regeneration efficiency are acquired with the increasing spacer length. It would be helpful to interpret what role the electron deficient π-spacers with varied lengths will play and how they are expected to behave in the performance of sensitizers. In this regard, this study presents us a promising way to design novel functional dyes and to utilize the potential advantages of the lengthy spacer dyes.