Small Molecule Acceptors Based On [1,2,5] Thiadiazolo[3,4-g] Quinoxaline For Broadband-detection

Broadband photodetectors attract extensive attention due to their expanding applications in environmental monitoring,astronomical exploration,machine vision,health detection,military applications,and other fields.Organic photodetectors（OPDs）as the candidate for next-generation photodetectors,not only compensate well for the shortages of the traditional inorganic photodetectors in terms of high cost,and their rigidity but also has the advantages of easy band gap adjustment and solution method preparation.Although non-fullerene acceptor（NFA）small molecules have been the dominant research direction in the past few years because of their well-defined material structure and good reproducibility,and high molar extinction coefficient.However,the high-performance NFA small molecules at this stage are difficult to meet the detection demand of covering the short-wave infrared band due to their wide band gap.In this thesis,we designed and prepared a series of ultra-narrow bandgap NFA small molecules and investigated the relationship between the material structure and the performance of broadband OPDs.The specific research of this thesis is described as follows:1.NFA TQpp based on A-D-A’-D-A structure by using electron-withdrawing core[1,2,5]thiadiazolo[3,4-g]quinoxaline（TQ）,electron-rich unit cyclopentadienthiophene derivative（DTC）as the linker unit,and electron-withdrawing 2-（5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene）malononitrile（2FIC）as the end group.The TQpp achieves an absorption spectrum of more than 1200 nm by strong intramolecular charge transfer effect and quinone conjugation effect.And we designed and synthesized NFA small molecules TQFF and TQCC with absorption spectrum over 1200 nm based on the introduction of halogen group elements into TQpp molecules.The OPDs prepared with TQpp,TQFF,and TQCC as the acceptor PTB7-Th as the donor,respectively,achieved a broadband response of 350-1300 nm.the D^*of the TQpp:PTB7-Th OPD can approach10¹² Jones in the 900-1100 nm,with an EQE peak of 30.71%.TQFF:PTB7-Th and TQCC:PTB7-Th OPDs have higher R,carrier mobility,and exciton dissociation efficiency,with EQE peaks of 35.18%and 36.25%,and D^*capable of exceeding 10¹²Jones.2.Based on the aryl chains modification at the meta-and para-position of the TQpp molecule,small NFA molecules TQmop and TQpop with absorption spectra over 1200nm were designed and synthesized.Broadband OPDs were prepared using TQmop and TQpop as the acceptor PTB7-Th devices,respectively,where the spectral response of TQmop:PTB7-Th and TQmop:PTB7-Th OPD were comparable to TQpp:PTB7-Th OPD.The dark currents of TQmop:PTB7-Th and TQpop:PTB7-Th OPDs are significantly suppressed with the increase of the active layer thickness but the optical response performance is reduced with the peak EQE of 28.47%and 25.20%,respectively,and D^*can reach 10¹² Jones.3.Based on the fused ring substitution of TQpp,we designed and synthesized NFA small molecule TQn with absorption spectrum over 1400 nm and an optical band gap of only 0.93 e V.Broadband OPDs were prepared with TQn as the acceptor and PTB7-Th as the donor.However,due to the thermal injection and more severe carrier recombination the device photodetection performance was degraded with a peak EQE of 23.48%and D^*over 10¹¹ Jones.Overall,this thesis presents the designing and synthesizing of ultra-narrow bandgap NFA and,investigated the relationship between the material structure and the performance of broadband OPDs,providing a new idea for the design and preparation of high-performance NFA small molecules and the realization of highly sensitive broadband OPDs.