Huafei Sun

Theoretical design and screening of panchromatic phthalocyanine sensitizers derived from TT1 for dye-sensitized solar cells

Computational screening of new dyes is becoming an extremely powerful tool, especially when associated with experimental synthetic efforts that might eventually lead to new and more efficient products. Nine novel unsymmetrical zinc phthalocyanine complexes derived from TT1 were designed as sensitizer candidates for dye-sensitized solar cells with three peripheral -CH₃, -OH, -OCH₃, -OPh, -NH₂, -NHCH₃, -N(CH₃)₂, -NHPh and -N(Ph)₂ substituents as the donors and a carboxyl group as the acceptor. The molecular orbital and the electronic absorption spectra properties of these compounds were studied and compared to those of TT1 using the density functional theory and time-dependent density functional theory calculations at B3LYP level with the LANL2DZ basis set. The novel candidates bearing the -NH₂, -NHCH₃, -N(CH₃)₂, -NHPh and -N(Ph)₂ moieties as the donors were found to be very promising for providing higher efficiencies than that of TT1 or even the current 4.6% efficiency record held by PcS6. They have higher LUMO levels, smaller energy gaps and red-shifted absorption bands compared to those of TT1. The new absorption bands emerging in 450-600 nm regions may promote ZnPcL-NH₂, ZnPcL-NHCH₃, ZnPcL-N(CH₃)₂, ZnPcL-NHPh and ZnPcL-N(Ph)₂ from near infrared to panchromatic sensitizers. Further experimental synthetic efforts are in progress in our group to validate the predictions in this report.

Riemannian Means on Special Euclidean Group and Unipotent Matrices Group

Among the noncompact matrix Lie groups, the special Euclidean group and the unipotent matrix group play important roles in both theoretic and applied studies. The Riemannian means of a finite set of the given points on the two matrix groups are investigated, respectively. Based on the left invariant metric on the matrix Lie groups, the geodesic between any two points is gotten. And the sum of the geodesic distances is taken as the cost function, whose minimizer is the Riemannian mean. Moreover, a Riemannian gradient algorithm for computing the Riemannian mean on the special Euclidean group and an iterative formula for that on the unipotent matrix group are proposed, respectively. Finally, several numerical simulations in the 3-dimensional case are given to illustrate our results.

Substituent effects on zinc phthalocyanine derivatives: A theoretical calculation and screening of sensitizer candidates for dye-sensitized solar cells

A series of unsymmetrical phthalocyanine sensitizer candidates with different donor and acceptor substituents, namely ZnPcBPh, ZnPcBOPh, ZnPcBtBu, ZnPcBN(Ph)₂, ZnPcBNHPh, ZnPcBNH₂, ZnPcBNHCH₃ and ZnPcBN(CH₃)₂, were designed and calculated using density functional theory (DFT) and time-dependent DFT calculations. The molecular orbital energy levels, the molecular orbital spatial distributions and the electronic absorption spectra of the ZnPcB series molecules were compared with those of TT7 and TT8 to reveal the substituent effects of different donor and acceptor groups on the phthalocyanine compounds and select good sesitizer candidates. The results show that some of these compounds have considerably smaller orbital energy gaps, red-shifted absorption bands and better charge-separated states, causing them to absorb photons in the lower energy region. Several new absorption bands emerge in the 400-600 nm region, which makes it possible for them to become panchromatic sensitizers. This characteristic is superior to the phthalocyanine sensitizers reported previously, including the current record holder, PcS6. The sensitizer candidates screened in the current work are very promising for providing good performance and might even challenge the photon-to-electricity conversion efficiency record of 4.6% for phthalocyanine sensitizers.

Image watermarking using polar harmonic transform with parameters in SL ( 2 , R )

In this paper, a novel polar harmonic transform with parameters in SL ( 2 , R ) is proposed in order to increase the security of the watermark information. It is named as the Polar Linear Canonical Transform (PLCT) based on the linear canonical transform. Moreover, a watermarking scheme associated with the PLCT is presented, and the simulations are performed to verify the importance of parameters of the PLCT and improve the capabilities of the existing results on the watermarking informations security. The experimental results show that due to the varieties of parameters, if parameters chosen in the extraction process are inconsistent with those used in the embedding process, then the bit error rate is bigger which means it is worse than that of consistent parameters in the two processes. This confirms the fact that parameters of the PLCT have superior security for watermark information. HighlightsWe report on novel watermarking techniques associated with the linear canonical transform (LCT) which is one of the powerful tools in several areas such as image processing, signal processing and so on.By the help of LCT, a novel polar harmonc transform having a matrix parameter in the real special linear group SL ( 2 , R ) are proposed to improve the existing results on the watermark information security.The experimental results show that due to the varieties of parameters in SL ( 2 , R ) , if the parameters chosen in the extracting process are inconsistent with those chosen in the embedding process, the bit error rates are worse than those of consistent parameters in the two processes.This confirms the fact that the parameters of the proposed transforms have superior security for watermark information.

A natural gradient descent algorithm for the solution of discrete algebraic Lyapunov equations based on the geodesic distance

A new framework to calculate the numerical solution of the discrete algebraic Lyapunov equation is proposed by using the geometric structures on the Riemannian manifold. Specifically, two algorithms based on the manifold of positive definite symmetric matrices are provided. One is a gradient descent algorithm with an objective function of the classical Euclidean distance. The other is a natural gradient descent algorithm with an objective function of the geodesic distance on the curved Riemannian manifold. Furthermore, these two algorithms are compared with a traditional iteration method. Simulation examples show that the convergence speed of the natural gradient descent algorithm is the fastest one among three algorithms.

Information geometric characterization of the complexity of fractional Brownian motions

The complexity of the fractional Brownian motions is investigated from the viewpoint of information geometry. By introducing a Riemannian metric on the space of their power spectral densities, the geometric structure is achieved. Based on the general construction, for an example, whose power spectral density is obtained by use of the normalized Mexican hat wavelet, we show its information geometric structures, e.g., the dual connections, the curvatures, and the geodesics. Furthermore, the instability of the geodesic spreads on this manifold is analyzed via the behaviors of the length between two neighboring geodesics, the average volume element as well as the divergence (or instability) of the Jacobi vector field. Finally, the Lyapunov exponent is obtained.

Image watermarking via fractional polar harmonic transforms

Abstract. Invariant harmonic transforms based on the fractional Fourier transform are proposed in this paper. The so-called fractional polar harmonic transforms (FrPHTs) with the order parameter α are first defined, which are generalizations of the PHTs. Second, a watermarking scheme is presented and discussed in detail associated with the newly defined FrPHTs. Finally, the simulations are clearly performed to verify the well capabilities of the transforms on image watermarking, which show that the proposed transforms with suitable parameters outperform the traditional PHTs. In addition, the experimental results also demonstrate that the order parameter α has an effect on the performance of FrPHTs in the image watermarking robustness and can improve the watermarking safety.

Theoretical design and screening of alkyne bridged triphenyl zinc porphyrins as sensitizer candidates for dye-sensitized solar cells

Alkyne bridged porphyrins have been proved very promising sensitizers for dye-sensitized solar cells (DSSCs) with the highest photo-to-electric conversion efficiencies of 11.9% solely and 12.3% co-sensitized with other sensitizers achieved. Developing better porphyrin sensitizers with wider electronic absorption spectra to further improve the efficiencies of corresponding solar cells is still of great significance for the application of DSSCs. A series of triphenyl zinc porphyrins (ZnTriPP) differing in the nature of a pendant acceptor group and the conjugated bridge between the porphyrin nucleus and the acceptor unit were modeled and their electronic and spectral properties calculated using density functional theory. As compared with each other and the experimental results of the compounds used in DSSCs previously, the molecules with a relatively longer conjugative linker and a strong electron-withdrawing group such as cyanide adjacent to the carboxyl acid group seem to provide wider electronic absorption spectra and higher photo-to-electric conversion efficiencies. The dye candidates ZnTriPPE, ZnTriPPM, ZnTriPPQ, ZnTriPPR and ZnTriPPS designed in the current work were found promising to provide comparable photo-to-electric conversion efficiencies to the record 11.9% of the alkyne bridged porphyrin sensitizer YD2-o-C8 reported previously.

Theoretical screening of novel alkyne bridged zinc porphyrins as sensitizer candidates for dye-sensitized solar cells

Alkyne bridged porphyrin sensitizers have attracted great attention in the field of dye-sensitized solar cells (DSSCs) because of their excellent photo-to-electric conversion efficiencies, among which YD2 has reached 11% while YD2-o-C8 has reached 11.9% solely and 12.3% co-sensitized with other sensitizers. Design and screening of porphyrin sensitizer candidates with wider electronic absorption spectra to further improve the photo-to-electric conversion efficiencies of corresponding solar cells is still very important. Twenty novel alkyne bridged zinc porphyrin sensitizer candidates composed of the donors diarylamino-, tri-4-methylphenyl-, tri-hydroxyl- and tri-amino-substituted zinc porphyrins as well as the selected acceptors E, M, Q, R and S have been designed and calculated at the density functional B3LYP level. YD2 and YD2-o-C8 are also calculated at the same level for comparison. The result shows that the sensitizer candidates all have smaller HOMO-LUMO gaps as well as wider and red-shifted absorption bands than those of YD2 and YD2-o-C8. Most of the sensitizer candidates have appropriate HOMO and LUMO energy levels relative to the redox potential of the mediator and the TiO2 conduction band, showing that they are promising to provide comparable or even higher photo-to-electric conversion efficiencies than 11% of YD-2 or 11.9% of YD2-o-C8.

Optimal control on special Euclidean group via natural gradient algorithm

Considering the optimal control problem about the control system of the special Euclidean group whose output only depends on its input is meaningful in practical applications. The optimal control considered here is described as the output matrix is as close as possible to the target matrix by adjusting the system input. The geodesic distance is adopted as the measure of the difference between the output matrix and the target matrix, and the trajectory of the control input obtained in the process is achieved. Furthermore, some numerical simulations are shown to illustrate our outcomes based on the natural gradient descent algorithm for optimizing the control system of the special Euclidean group.创新点本文借助于自然梯度算法研究特殊欧几里德群的最优控制问题。这一控制系统的输出仅仅与控制输入有关。具体来说, 文中考虑的特殊欧几里德群上的最优控制问题为: 通过调节系统的输入, 使得系统的输出矩阵尽可能的接近目标矩阵, 输出矩阵与目标矩阵的差异用相应矩阵流形的测地距离来描述, 同时, 在控制过程中, 可以得到系统输入的控制轨线。在文章的最后, 利用数值模拟进一步说明文中利用自然梯度算法来解决特殊欧几里德群的最优控制问题的可行性和有效性。