Synthesis And Characterization Of Benzothiadiazole Aromatic Heterocyclic Non-fullerene Electron Acceptor Materials

After nearly two decades of development,the advantages of organic solar cells（OSCs）as a new generation of solar cells are very obvious,including low price,light weight,flexible devices,and so on.So far,the conversion efficiency of organic solar cells has reached more than 18%.For a long time,fullerene derivatives have been the most widely used electron acceptors because of their spherical molecular structure,which can make them compatible with a large number of donor materials.However,fullerene derivatives as electron acceptors also have many shortcomings,such as weak visible light absorption,difficult to control electronic energy levels,and easy aggregation in the thin film state,resulting in poor morphology and shorter device life,and the price expensive.However,non-fullerene（NF）as an electron acceptor can not only solve the disadvantages of fullerene acceptor.And it has a high molar absorption coefficient and great potential to achieve high conversion efficiency.Therefore,it has received great attention as a acceptor for organic photovoltaics（OPV）.This paper uses the modified benzothiadiazole（BT）and 5,5-bis（4-hexylphenyl）-5H-dithio[3,2-b:2’,3’-d]pyran（DTP）as the electron donating units,and the 2-（3-oxo-2,3-dihydro-1H-inden-1-yl）malononitrile（INCN）,2-（5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-yl）malononitrile（2FIC）,3-（2-ethylhexyl）rhodanine as the electron-deficient units.and a series of novel non-fullerene electron acceptors were synthesized.To study the absorption,energy level,molar absorption coefficient,aggregation performance and photovoltaic device performance of non-fullerene acceptor（NFA）materials by the introduction of fluorine atoms and the changes of different donating and electron-deficient units.In the second chapter,the DTP unit with strong electron donating ability is connected with the modified BT unit as the electron donating unit,and a new small molecule acceptors（SMA）named BTC8IC4F is synthesized and characterized with 2FIC as the end group.At the same time,in order to compare and study its photovoltaic performance,a fluorine-free NFA BTC8IC was synthesized with INCN as the end group.The effect of introducing fluorine atoms into the end groups on the photovoltaic performance of non-fullerene small molecule acceptors was studied.The results show that the two small organic molecules synthesized based on the DTP unit have broad spectral absorption.After fluorine atoms are introduced into the end groups,the molar absorption coefficient increases by 1.72 times,and the absorption spectrum in the solid state film state is slightly blue shifted and the aggregation performance of the molecules is enhanced,and the energy level is reduced.Matching with the polymer PBDB-T,OSCs based on PBDB-T/BTC8IC have an optimal photovoltaic conversion efficiency（PCE）of 1.50%,an open circuit voltage(V_OC)of 0.76 V,and a short circuit current density(J_SC)of 6.16 m A·cm^-2,The fill factor（FF）is 31.82%.Compared with the SMA BTC8IC of end groups are not fluorinated,the photovoltaic performance of OSCs based on fluorinated BTC8IC4F has improved to varying degrees.The PCE reached 1.86%,V_OCwas 0.69 V,J_SCwas 8.02 m A·cm^-2,and FF was 33.48%.It can be seen that the introduction of terminal fluorine atoms has a certain effect on the improvement of the photovoltaic performance of organic small molecule acceptors.In Chapter 3,the small organic molecule BTREH was designed,synthesized and characterized.The chemical structure contains a D-A-D electron-rich core,which includes BT（A）and DTP（D）,and is terminated by 3-（2-ethylhexyl）rhodanine.In the bulk heterojunction OSCs,the blend with the polymer donor PTB7-Th produced PCE of 1.12%,V_OCof 0.66 V,J_SCof 5.13 m A·cm^-2,and FF of 32.95%.There is not much difference in photovoltaic performance compared with indane end groups.This indicates that the small molecule acceptors of rhodanine end groups have great potential to further improve the PCE of OSCs.In Chapter 4,the DTP unit connected to alkoxythiophene was used as the electron-donating unit,the INCN and 3-（2-ethylhexyl）rhodanine were the electron-deficient units,respectively.Two A-D-D’-D-A organic molecules acceptors named DTPIC and DTPREH that can enhance the intramolecular charge has been designed,synthesized and characterized.The results show that the small organic molecule DTPIC based on the end group of indandione broadens the absorption spectrum compared with the DTPREH with rhodanine as the end group,increases the molar absorption coefficient,deepens the energy level,and provides a V_OCof 0.55 V,J_SCof 5.45 m A·cm^-2,FF of 33.78%,PCE of 1.01%of photovoltaic performance.