The Design And Theoretical Research On Porphyrin And DTF Pure Organic Sensitizers

Solar calls are devices that can convert solar energy to electric energy efficiently.Dye-sensitized solar cells(DSSCs)due to their abundant raw materials,simple fabrication process and low-cost production,have become a important branch of solar power industry.Dye sensitizers adsorbing to the surface of semiconductor are the key photoelectric conversion materials in DSSCs.The electrons in sensitizers transfer from the low level of ground state to the high level of excited state and generate effective potential difference when sensitizers are excited by light.Dye sensitizers can be broadly divided into metal centered dyes and pure organic dyes.Organic dyes are widely investigated and applied since they are easily designed and synthesed due to their diverse structures,superior to noble metal complexes in cost and environment.Theoretical investigations on properties of sensitizers can not only verify and analyse the experimental results but also provide new thought in designing and screening novel complexes as efficient dyes.In addition,theoretical investigations can also shorten the research time,reduce cost and material waste.In this thesis,we employed the idea “Donor(D)– ?-bridge – Acceptor(A)” and designed two kinds of sensitizers under the background of corresponding experimental researches.Based on the molecular geometry of the reference dye YD2-o-C8,we designed a series of Zn centered porphyrin dyes by changing the ligands on donor and bridge group using phenyl,phenoxyl,thiophenyl naphthyl groups.And based on the molecular geometry of the reference dye DTF-C3,we gained three kinds of dithiafulvenyl(DTF)– based pure organic dyes by changing the bridge groups using carboxylic and dipicolinic acid groups;changing the bridge groups using fluorenyl,benzothiadiazolyl(BTD)and quinoxalinyl groups;changing the donor groups using DTF substituted triphenylamine hybrid group.We investigated characters of sensitizers in ground and excited states using the density functional theory(DFT)and time-dependent DFT approach in tetrahydrofuran(THF)solution.We evaluated the effects of functionalized donor,bridge and acceptor groups on sensitizers by analyzing the molecular geometries,molecular orbitals and electronic structures,optical absorption spectra,and light-harvesting efficiency.Our results are shown as follows:(1)For Zn centered porphyrin dye sensitizers,bithiophenyl,biphenyl,and naphthyl groups on bridge decrease the energy level gaps and dithiafulvenyl,carbazolyl and naphthyl groups on donor subunit increase the gaps.The optimizations on bridge groups lead to obvious red shift of spectra with stronger intensities at the long wavelength region and that on donor subunit promote the absorption intensity significantly.Compared with the reference dye YD2-o-C8,the designed porphyrin dyes show better light-harvesting efficiency and coverage range along with the structural optimizations on bridge and donor groups.(2)For DTF sensitizers with different acceptor groups,the alterations on acceptor subunit change the lowest unoccupied molecular orbital(LUMO)and then result in the variations in energy level gaps.The absortion apectra of sensitizers with carboxylic and dipicolinic acid groups as acceptor subunits show blueshift relative to that with cyanoacrylic acid group.(3)For DTF sensitizers with different bridge groups,bridge groups can tune the highest occupied molecular orbital(HOMO)and LUMO appropriately.Notbly,thiophenyl and quinoxalinyl groups can reduce the energy level gaps more effectively than other bridge groups in sensitizers.Compared with dye DTF-C3,the absoption spectra of sensitizers with fluorenyl group as bridge exhibit blueshift;the absoption spectra of sensitizers with 3,4-ethylenedioxythiophene(edot)and alkylsubstituted dithienosilole(dts)groups as bridge show redshift obviously and the absorption bands broaden,but the absortion strength decrease to some extent;sensitizers with thiophenyl,quinoxalinyl and BTD groups as bridge have one more weak absorption band at the short wavelength region,the spectrum at the long wavelength region have obvious redshift but the absorption strength reduce to some extent.(4)For sensitizer with DTF substituted triphenylamine hybrid group as donor subunit,the hybrid donor can reduce the energy level effectively relative to the DTF donor.The absoption spectrum of sensitizer with the hybrid group as donor has one more absorption band at at the short wavelength region and has small redshift but weaker absorption strength at the long wavelength region relative to that with the DTF as donor.This theoretical investigation would facilitate the screening of the functionalized acceptor,bridge and donor groups for efficient porphyrin and DTF dyes in DSSCs.