Theoretical Design And Optoelectronic Properties Based On Linearly Efficient Zn-Porphyrin Small Molecules Donor

Organic photovoltaic(OPV)cells have received extensive attention owing to the light weight,low cost and translucency advantages.Among the numerous device structures,bulk heterojunctions(BHJ)were widely used,due to form an interpenetrating network structure through interleaving of acceptor and donor molecules in active layer,which increases the interface contact area and facilitates effective exciton dissociation and transport.Wherein,reasonable design of active layer material is one of the key factors to enhance device performance.Designing novel and efficient OPV materials based on the traditional trialand-error method usually time consuming and resource costing.Therefore,establishing the relationship between molecular structure,active layer morphology as well charge transfer(CT)process at the donor/acceptor interface by using theoretical characterization methods,will help further improvement of molecular design and performance.Theoretical chemistry focuses on using mathematics,physics and computers methods to explore the general laws of atoms,molecules,molecular aggregates and condensed phases,and accurately predict their properties.On the one hand,it is possible to obtain static and dynamic information on chemical problems from the microscopic to macroscopic levels by means of calculations and simulations,so that more and more experimental phenomena and data can be presented though calculations and correctly interpreted.On the other hand,theoretical chemistry can explore unknown chemical phenomena by proposing new concepts and methods,provide predictor and guide for designing of new functional materials.Moreover,theoretical and computational chemistry has widely applications,also is an indispensable tool for solving scientific problems for life sciences,energy sciences,materials sciences,and environmental sciences,and other intersection fields.Theoretical chemistry not only provide solid foundation for molecular science,established the computational methods have also been widely used by researchers in many fields.Therefore,in this dissertation,choosing porphyrin and its small molecule derivatives as research objects,owing to their adjustable structure,strong absorption,high molar extinction absorption,and unique energy transfer properties.Adopting density functional theory(DFT),the time dependent-density functional theory(TD-DFT)combined with molecular dynamics(MD)simulations methods to clarify the interrelationships between fragments changes before synthesizing new materials,and establish the corresponding design rules.To achieve purposeful screening and combination of fragments to solve the pre-rational design of materials in the field of optoelectronic functional materials,and it is expected to provide theoretical guidelines for designing well-performing OPV material.The main research components are as follows:1.A structural modulation strategy of porphyrin small molecule donor toward high open circuit voltage(Voc)for OPVPCE is an important indicator to measure the performance of OPV devices,the Voc is one of the key parameters affecting PCE.However,there is lack of clear rules on how to enhance Voc based on molecular design.Herein,porphyrins with A-π-D-π-A structure were selected as research objects,a new molecular design strategy was proposed by exploring the inter-fragments interactions,and nine fragments were used to screen and confirm.The results indicate that the highest occupied molecular orbital(HOMO)energy level of the porphyrin small molecule donor can be significantly reduced by applying this strategy,and enhanced the VOC without losing of short-circuit current(JSC)as well filling factor(FF).This work not only provides a strategy for screening π-bridge and breaks the limitation of molecular fragment selection.Moreover,it theoretically elucidates the effect of π-bridge alteration on the photoelectric properties of molecules,which provides valuable theoretical guidance for further design and synthesis of new high-performance small molecule donors.2.Small molecule design rules for panchromatic absorption range regulation with high VOCAlthough porphyrin small molecules have more advantages,the inherent absorption defect at green light limits their widely application in OPV.Therefore,the relationship between the change of π-bridges and absorption range was elucidated based on the modification of π-bridges of porphyrin molecules with A-π-D-π-A structures.And choose non-fullerene acceptor(NFA)to match with it to explore the universality of porphyrin-based donor material application.The results show that π-bridges and side chains interaction in the molecule lead to different intramolecular charge transfer(ICT)ways was the key to achieve panchromatic absorption and expand the absorption range to near infrared region(reach to 1200 nm).Moreover,there are exist different CT mechanism when combined with NFA,the rate ratio of charge transfer(kinter-CT)and recombination(kinter-CR)as high as 1011 s-1 and VOC greater than 1.0 V,expected to break the imbalance between VOC and JSC.3.The effect miscibility degree of porphyrin small molecule donors and NFA on exciton dissociation processes in OPV deviceCurrently,the devices are based on the excellent performance of porphyrin donor and NFA has fewer researches as well low performance.Whether it is related to the interfacial exciton dissociation process is still unclear.Therefore,we chose mono and dimer porphyrin donors to combine with different kinds of NFA to explore the reasons.The effects on microscopic morphology of complexes,the degree of mixing,spacing of donor and acceptor,interactions and CT were analyzed from an interfacial perspective,combining of quantum chemistry(QC)and MD methods.The results show that porphyrin materials have strong crystallinity to increase the spacing,lead to lower miscibility and weaken the intermolecularπ-π stacking.Although high kinter-CT were obtained based on the screened optimal model,the large phase separation resulted in a low number of such conformations.The small number of high-energy CT states also reduces the pathway for exciton dissociation,and becomes one of the potential reasons for limiting the PCE improvement.This can be improved by modifying the side chain of molecule terminal group.The comparison results also indicate that the effective exciton dissociation is more readily available for all porphyrins OPV devices,resulting in kinter-CR lower than nearly four orders of magnitude and had higher VOC,indicating greater promise for development.