Theoretical Insight Into The Dye-sensitized Structural Modifications And Electron Transfer Mechanism In DSSCs

Dye-sensitized solar cells(DSSCs)have been widely researched for their evident advantages of low-cost and high efficiency in converting solar energy to electricity.A deep understanding of the working mechanism of dye-sensitized solar cells plays a key role in improving the photoelectric conversion efficiency of the cell.Dye sensitizers are one of the most important components in DSSCs.Dyes are used to capture sunlight and carry out interface electron transfer.Reasonable structural modification of dye sensitizers can effectively improve cell efficiency.Theoretical calculations can predict and assist experiments,reveal the working mechanism of dye-sensitized solar cells from atomic details and characterize the important effects of different components on the efficiency of DSSCs.This paper studied extensive research of Ru(II)complex dyes and organic dyes,and discusses the influence of the microstructure of dye molecules on DSSCs performance from the theoretical investigation,so as to provide helpful theoretical guidance for experimental optimization of the efficiency of DSSCs device.The related research contents are as follows:Neutral ligands are usually used in ruthenium complex dyes,but anionic ligands have received less attention.Based on this,The effect of anionic ancillary ligands of Ru(II)complex dyes on the performance of dye-sensitized solar cells was reported.Three Ru(II)complex dyes with neutral or anionic tetrazolyl ligands was specifically discussed.The geometrical structures,electronic structures,absorption spectrum and interface interaction of dyes are determined by density functional theory and timedependent density functional theory methods.The calculation results show that anionic ancillary ligands can efficiently enhance the electron donating ability,increase the energy levels of occupied orbitals,and enhance the light-harvesting ability.And it can improve intramolecular charge separation and inhibit energy loss channels.To clarify how anionic auxillary ligands affect charge transfer at the dye/Ti O2 interface,quantum dynamics simulations were performed.The research results show that the choice of the initial electronic state strongly affects the interface electron transfer,and the introduction of anionic groups can effectively accelerate the interface charge transfer.In general,simulation results are consistent with the experimental research,which helps to understand how anionic tetrazolium ligands can improve device performance.This work suggest that the experimental design of efficient dyes can be extended to the Ru(II)complex dyes containing anionic ligands.The effect of the difference in the substitution position of the anchor group for the Ru(II)complex dyes on the photoelectric performance of DSSCs was studied.The experimentally synthesized Ru(II)complex dye K1 with square planar tetradentate ligand as the reference dye was discussed,and designed three dyes(Ru1,Ru2,and Ru3)by increasing the conjugation strongth of the ancillary ligands and changing the substitution position of the anchor group.Experiments confirmed that because K1 has a highly conjugated ancillary ligands that shows obvious advantages over the wellknown dye N749 in light absorption capacity.Therefore,it is used as the parent dye to further modify the structure and characterize the properties of different dyes in detail.The light absorption properties,electronic structure properties,intra-molecular or molecule to interface charge transfer that affect the performance of dyes are discussed in depth.The calculated results show that Ru1 containing arylmethane groups has higher light absorption and interfacial electron transfer efficiency than the reference dye K1.The position of the anchor groups with carboxylic acid can largely control the rate of interfacial electron transfer was confirmed.Because changing the position of the anchor group results in a different degree of electron donor-acceptor orbital interaction,Ru3(an anchor group attached to pyridine rings)has faster interfacial electron transfer than Ru2(an anchor group attached to a pyrrole ligand).The effects of the conjugation extension of ?-bridges in organic dyes and the structural modification of electron donor group on the performance of dyes was systematically studied.Through a variety of design strategies to manipulate the electron donor and ?-bridges groups of organic dyes,a series of promising organic D-?-A dyes was theoretically designed.The optical characteristics,intramolecular charge transfer properites,dye recombination between dye and electrolyte I2,dye regeneration and interface electron injection of the separated dye and dye-Ti O2 combined system was ayalyzed.Explained in detail the reason for contradiction with the traditional view: why the extension of ?-bridge have the DSSCs with low efficiency.This work show that dyes with further extended ?-bridges have a gradually red-shifted absorption spectrum,but the highest occupied molecular orbital(HOMO)energy level to decrease,due to the unfavorable energy alignment between dye HOMO and redox potential of electrolyte,thus the increase of the charge recombination between the injected electrons and the electrolyte leads to the low dye regeneration efficiency,which reveals the key reason for the degradation of DSSCs performance.Further substitution of the triphenylamine donor with carbazole or coumarin electron donor groups can reduce HOMO level and avoid inefficient dye regeneration problems,while retaining other beneficial properties.Finally,a sensitizer with high light absorption efficiency and dye regeneration efficiency was designed.The electron acceptor group can strongly influence the interface electron transfer and control the performance of DSSCs,so it is worthy of further discussion.A series of anchors for dye-sensitized solar cells application,and paid attention to the potential of anchors based on novel pyridinium ylides was theoretically studied.The optical spectrum,the shift of Ti O2 conduction band edge and interface electron transfer of the isolated dyes and dye/Ti O2 are analyzed by quantum chemistry calculations.The key parameters affecting short-circuit current and open-circuit voltage are comprehensively evaluated to analyze the performance of different anchor groups.The results show that the anchors based on pyridinium ylide is inherently beneficial to light-harvesting and improve intramolecular charge transfer,and moves the edge of the conduction band of the Ti O2 semiconductor upward,thereby further increasing the short-circuit current and open-circuit voltage.Due to the stronger donor-acceptor interaction,the conjugated rhodanime-3-acetic anchor exhibits faster electron injection than the non-conjugated structure.Theoretical calculation results show that the potential of anchors based on novel pyridinium ylide compared to the traditional carboxylic acid and rhodanime-3-acetic,revealing the key role of local structure changes in the interface electron transport.