Synthesis And Study Of BTA-based Non-fullerene Small Molecule Acceptor Materials

Among of organic solar cells,the classical acceptor fullerenes have thedisadvantages of the difficult modification of energy levels and absorption spectra.In contrast to the fullerene,small molecular acceptors(SMAs)have become hot researching field and drawn more and more attention due to their simple and diverse synthesis and purification methods,defined molecular mass and structure.When P3HT is used as a donor,SMAs should have high-lying energy levels to match well with P3HT,and their geometries should also be carefully engineered in order to form appropriate blend morphology with P3HT in the active layer.In this study,we synthesize a series of non-fullerene small molecule materials through molecular design and explore its application in organic solar cells.The main contents include the synthesis of benzotriazole(BTA)-derived small molecule materials based on benzotrithiophene and spirofluorene as the molecular center units,the investiagtion on the electronic structures,and the characterization on the photovoltaic devices.The device with non-fullerene SMAs with weak electron-deficient unit BTA as the acceptor shows high VOC,and SF can be used as central core because the three-dimensional space structure can very well inhibit the self-aggregation in the film and finaly tune the blend morphology.Therefore,spirofluorene(SF)and benzo[d][1,2,3]triazole(BTA)are considered as promising components for constructing n-type photovoltaic materials.Three new small molecule acceptors(SMAs)named as BTA21,BTA23 and BTA27 with the structure of A2=A1-D-A1=A2 have been designed,in which SF and BTA were used as central unit of D and bridged acceptor unit of Ai respectively In addition,3-ethylrhodanine,malononitrile were chosen as terminal acceptor units to modulate the properties of final SMAs.The best PCE value of the P3HT:BTA21 device is 3.28%,VOC is 1.02 V,JSC is 5.45 mA.cm-2,and FF is 0.59.BTT-3BTA1 and BTT-3BTA2 were synthesized with benzotrithiophene(BTT)which has a completely coplanar rigid structure with strong electron pushing ability and high hole mobility,as the core.BTA as the acceptor unit.Their optical and electrochemical properties were investigated.The best PCE value for the P3HT:BTT-3BTAI OSC is 2.23%,VOC is 0.89 V,JSC is 4.65 mA cm-2,and FF is 0.54.Similarly,SF was also used as the central core,with four BTA units were covalently bonded.SF-4BTA1 and SF-4BTA2 were synthesized and characterized.The best PCE value of the P3HT:SF-4BTA1 OSC is 3.48%,Voc is 1.01 V,Jsc is 6.51 mA cm-2,and FF is 0.53.We found that the end groups have a great influence on their intermolecular interactions and therefore play an important role in their performance.