Synthesis And Properties Of Non-Fullerene Organic Solar Cell Receptor Materials Based On Thiophene Derivatives

Today,the harm caused by traditional energy to the environment is becoming more and more serious,however,people's demand for energy is constantly expanding.Therefore,people have to find a clean,renewable energy.Among many new energies,solar energy occupies an important position,and the solar cell is the most effective way of using solar energy.Organic solar cells(OSCs)have been attracting a lot of attention due to their low cost,light weight,easy modification,and possibility of creating large-area devices,Fullerene and its derivatives have dominated acceptor materials.However,the drawbacks of fullerenes such as the difficulty of purification,high cost,weakly absorbing in the UV-visible region of the solar spectrum limit the development of OSC technologies.In order to broaden the absorption range,control the HOMO and LUMO energy levels,and improve the hole mobility and electron mobility of the photosensitive materials,we designed and synthesized a series of non-fulerene small molecule electron acceptor materials containing benzodithiophene(BDT)and indacenodithienothiophene(IDTT)units,and the target compounds were characterized by nuclear magnetic resonance(NMR),matrix assisted laser desorption ionization time of flight mass spectrometry(MALDI TOF MS)and elemental analysis(EA).The thermal,photophysical,electrical properties and photovoltaic performance of the target compounds were analyzed by using thermogravimetric analyzer(TGA),differential scanning calorimetry(DSC),UV-visible absorption(UV-vis),cyclic voltammetry(CV),and so on.In the first part of the experiment,we chose BDT as the electron donor moiety of the acceptor materials,which has good planarity and tends to form ?-?stacking.In the second chapter of this paper,two kinds of A-D-A type non-fullerene small molecule acceptor materials,BDT-BBT2 and BDT-BTF2,were synthesized by introducing units with different electron-withdrawing abilities on both sides of BDT unit.The decomposition temperatures,Tds,of BDT-BBT2 and BDT-BTF2 at weight loss of 5%were 272 ? and 215 ? respectively.The glass transition temperatures,Tgs,were 251? and 180?,respectively,showing good thermal stability and morphological stability.Both acceptors exhibited strong absorption from 300 nm to 600 nm,which is complementary to that of the excellent donor material PCE-10.It is expected that the photovoltaic devices prepared with these two materials might have excellent performances.In the second part of the experiment,five kinds of A-D-A type non-fullerene small molecule acceptor materials were synthesized by using stille coupling reaction and optimizing the synthetic route using IDTT as the elecreon donor moiety.IDTT is chosen because it has excellent rigid planar structure and large degree of conjugation,which is conducive to the delocalization of ? electrons and the enhancement of carrier transport capability.The target compounds,IDTT-DBF2,IDTT-BCT2,IDTT-BTC2,IDTT-BDF2 and IDTT-CDT2,have different electron withdrawing moieties and different degree of?-conjugation.In the UV-visible experiments we found that they had strong absorption between 300 and 800 nm.Besides,the synthetic materials also exhibited good thermal stability,and their Tds were 394 ?,205 ?,424 ?,360 ?,and 432 ?,respectively.IDTT-BTC2 and IDTT-CDT2 were used to characterize the performance of the device.The photoelectric conversion efficiency(PCE),open circuit voltage(Voc),short circuit current density(Jsc)and fill factor(FF)of the device based on IDTT-BTC2 were 0.5%,0.93 V,1.11 mA/cm2,and 0.48,respectively.These parameters were improved to be 0.90%,1.02 V,2.39 mA-cm-2 and 0.37,repectively,after device optimization by annealing.Compared with the performance of the unannealed device,PCE,and Jsc are in creased by 80%,and 115%,respectively,while the voltage change is not obvious.In summary,seven target compounds with excellent properties were designed and synthesized based on the principle of molecular engineering.Their device performances such as Voc,FF,Jsc and PCE were studied.The devices can be optimized through the choice of solvents and additives,adjusting the donor/acceptor ratio,altering the thickness of the active layer and changing the annealing conditions.