Synthesis And Properties Of Wide Band GAP 3D Non-fullerene Small Molecule Acceptor Materials Based On Spirobifluorene And Bifluorenylidene

Non-fullerene small molecule acceptor materials have become the main focus of research in bulk heterojunction organic photovoltaic cells?BHJ-OPVs?due to their clear molecular structure,high purity and better batch-to-batch reproducibility.This paper introduced the advantages,disadvantages and research status of two types of non-fullerene small molecule receptor materials,both planar and non-planar.In order to obtain the high energy conversion efficiency?PCE?of BHJ-OPVs,three novel D-A₄ non-fullerene 3D small molecule acceptor materials were designed and synthesized.The relationship between thermal stability,photophysical properties,electrochemical performance and photovoltaic performance of such materials was investigated in detail.The specific research is as follows:1.A wide band gap 3D small molecule acceptor?SF?BR?₄?based on spirobifluorene?SF?core,which is flanked with 2,1,3-benzothiadiazole and end-capped with 3-ethylrhodanine groups is synthesized.Compared with the narrow band gap donor material PffBT4T-2OD,SF?BR?₄ showed the characteristics of well energy-level matching and complementary absorption.In addition,the three-dimensional?3D?molecular geometry of SF?BR?₄ helps to inhibit excessive self-aggregation between molecules in the PffBT4T-2OD:SF?BR?₄ blend films,which are beneficial to obtain stable devices.The PCE based on the PffBT4T-2OD:SF?BR?₄device was 6.15%.To the best of our knowledge,6.15%is the highest PCE value for current photovoltaic devices based on 3D non-fullerene small molecule acceptors,in addition to the phthalimide derivative 3D small molecule acceptor materials.2.Based on the study of molecular SF?BR?₄,a new 3D small molecule acceptor material SF?BRCN?₄ was obtained by modifying the terminal alkyl chain and a stronger electron withdrawing group.Compared with the absorption spectrum of molecular SF?BR?4,the absorption of SF?BRCN?4 in both solution and solid film were red-shifted,and showed a significant broadening and red shift at 400 to 650 nm,which proved the end group changes from 3-ethylrhodene to a dicyan-3-hexylrhodanine group,the intramolecular charge transport?ICT?effect is enhanced and the arrangement between the molecules becomes more ordered.Based on the device of PBDB-T-SF:SF?BRCN?₄,the PCE is as high as 7.18%,with a high Voc of 1.03 V,a Jsc of 11.62 mA cm^-2,and an FF of 0.60.Studies have shown that the appropriate increase of the terminal alkyl chain and electron withdrawing groups is an effective way to improve photovoltaic materials.3.Based on the study of molecular SF?BR?₄,the effect of new nuclear 3D on the performance of small molecule receptors was explored by designing and synthesizing molecular BF?BR?4.By comparison analysis of the absorption spectra of SF?BR?4 and BF?BR?₄,it is known that the absorption spectrum of BF?BR?₄ is slightly broadened,which can be attributed to the conjugated 3D molecular structure of the molecule.The PCE based on the device of PBDB-T-SF:BF?BR?₄ was only 0.88%due to the energy level mismatch of the donor-acceptor materials and the poor morphology of the active layer film.