Design and Synthesis of Donor Materials Based on Star-shaped Magnesium Porphyrin Molecules and Application in Photovoltaic Performance

Author:Wang Huan

Supervisor:song wei zuo yutaka matsuo


Degree Year:2019





The main work of this thesis is based on the design and synthesis of magnesium porphyrin donor materials and the preparation of devices,especially for the morphology control.The use of different aromatic groups and acceptor units through the acetylene bridge in the molecular skeleton of magnesium porphyrin to construct the intramolecular donor and acceptor system to regulate the charge transfer intensity and intermolecular interaction of the target molecule.At the same time,by changing the type of aromatic group,the number of acceptor units,the selenium substitution effect of the acceptor units,the terminal alkyl modification of the acceptor units,which could regulate the light absorption,energy level and matching,mobility,charge separation and recombination,phase separation scale and power conversion efficiency of the target molecules.Finally,we developed the donor materials with power conversion efficiency exceeding 5.7%,6.1%and 7.4%,which have important guidance and significance for the donor material’s design.In the second chapter,Based on the magnesium tetraacetylene porphyrin precursor and four acceptor units(S-DPP),the target molecule Mg-TEP-(S-DPP)4 is synthesized by the Sonogashira coupling reaction with D-(π-A)4 framework.Through subsequent electrochemical and photophysical measurements,we found that this star molecule has the following advantages:First,strong and broad light absorption in the visible and NIR regions,resulting in enhanced intramolecular charge transfer and red-shifted UV-visible absorption,which is beneficial for better light-harvesting and higher short-circuit current density(Jsc);Second,a narrower band gap decreases energy loss(Eloss=Eg-qVoc),which is important in realizing high PCE;Third,star-shaped porphyrins have favorable intermolecular interactions and aggregation behavior,where solvent molecules such as pyridine coordinated to the metal(II)center to powerfully suppress excessive aggregation and promote the ordered arrangement of molecules in blended films;Fourth,their planar configuration contributes to intermolecular π-π stacking,leading to high carrier mobility.Based on the above advantages,through morphology control and device optimization,we finally achieved high power conversion efficiency(PCE)of 7.4%.In the third chapter,the electron-rich and heavy atomic effects of selenium(Se)and terminal alkyl modifications are used to modify the acceptor units to construct a new target molecule Mg-TEP-(Se-DPP)4.We systematically exploring the relationship between selenium substitution and energy level(HOMO and LUMO level),energy gap,intramolecular charge transfer and absorption spectrum,exciton dissociation and charge recombination.Based on the obtained experimental data an in-depth analysis leads to the following conclusions:a)a narrower band gap;b)more closely matched energy levels;c)extensive absorption in both the ultraviolet and visible-NIR regions,and d)slightly poorer morphology of blended films.Thermal annealing,solvent vapor annealing,solvent and additive doping were introduced to control the blended film’s morphology.Finally,we obtained 6.1%PCE.In the fourth chapter,based on the previously reported D-(π-A)2 molecular skeleton,we systematically studied the effect of the aromatic group substitution on the photovoltaic efficiency.Finally,we found that only the n-hexyl aromatic group can significantly promote the morphology of blended film to obtain a nanoscale phase separation which is beneficial to achieve a high fill factor(FF).Furthermore,the target molecule Mg-TEP-DPP2Ar2 with a n-hexyl aromatic group has a superior solubility to achieve a higher concentration of the active layer,and finally obtained a moderate PCE of 5.73%.