Synthesis And Properties Of Organic Photovoltaic Materials Based On Pyrene And Dithiophenobenzothiadiazole

In recent years,with the rapid development of organic solar cells(OSCs),the continuous development of new materials and the continuous optimization of device conditions,the energy conversion efficiency(PCE)of a single device have already exceeded 18%,which indicates that OSCs have a great potential for commercialization.Polymer donor and small molecule acceptor are two kinds of active layer materials commonly used in photovoltaic devices.The polymer donor has the advantages of easy modification of chemical structure,adjustable energy level,large molecular weight and stable chemical structure and photovoltaic performance.The advantages of small molecule acceptor are molecular weight determination,accurate structure,easy purification,short synthesis cycle and so on.Two small molecule acceptor materials and two polymer donor materials were designed and synthesized by considering the chemical structure,absorption spectrum,solubility and phase morphology of the blends.The synthesized molecules were characterized by time of flight mass spectrometry(MALDI-TOF),elemental analysis and nuclear magnetic resonance spectroscopy(NMR)and so on.The thermal stability,photoelectric and photovoltaic properties of the target molecules were systematically studied.The main contents are as follows:(1)The small molecule acceptors T1 and S1 were synthesized by using the electron donor unit(D)rigid pyrene as the nucleus,the indacenodithiophene(IDT)as?bridge and the 5,6-difluoro-1,3-indanone(2FIC)as terminal electron-withdrawing unit(A).The effects of single and triple bond bridging on the molecular structure,photoelectric properties,carrier transport properties and photovoltaic properties of small molecule receptors were systematically explored.The results showed that T1 had better solubility and larger molar extinction cofficient;so that T1 obtained high short-circuit current density(J_sc).The lower HOMO level enabled a higher open circuit voltage(V_oc).The blends of acceptor T1 and donor material PBDB-T had better solubility,higher electron mobility(?_e)and better active layer morphology.The bulk heterojunction(BHJ)device based on PBDB-T and T1 showed optimal PCE of 4.86%with V_oc of 0.90 V.(2)Two new terpolymers P20 and P40 were synthesized by adding fDTBT,an electron acceptor unit in D18 polymer structure,with the structure unit of PM6 in different proportions of 20%and 40%.The effects of fDTBT on the molecular structure,photoelectric properties,photovoltaic properties and carrier transport properties of the terpolymers were systematically studied.The results showed that the HOMO level,crystallinity and mobility of the polymer were improved with the fDTBT content decreased from 40%to 20%.Due to the above advantages,the device based on P20:Y6showed more efficient exciton disintegration,higher and more balanced hole and electron mobility after adding 0.5%DIO additive,and finally obtained PCE value of16.21%(J_sc=27.97 m A·cm^-2,V_oc=0.84 V,FF=69.32%),much higher than P40:Y6based devices(PCE=14.90%).