Synthesis And Properties Of Both Triazine Bridging Stepped Levels Of Organic Photoelectric Materials

Inspired by the photosynthesis of green plants,two types of Donor-Acceptor1-Acceptor2(D-A1-A2)compounds indoline-triazine-fullerene(YD-TRC-ABF)and indoline-triazine-anthraquinone(YD-TRC-AEAQ)with energy level cascades were synthesized and the structures were confirmed by 1H NMR and mass spectrometry.The spectral and electrochemical properties of these compounds were investigated using UV-visible absorption spectroscopy,steady-state fluorescence spectroscopy,cyclic voltammetry and transient fluorescence spectroscopy.The results indicated the cascades of the highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)energy levels.This energy level distribution facilitated the electron transfer from the donor group to the Acceptor1 and further to the Acceptor2 as well as the hole transfer from acceptors to the donor.The charge-separated state or triplet state of the two compounds were detected and analyzed based on the nanosecond transient absorption spectra.The results indicated that the charge separation and triplet states coexisted in YD-TRC-ABF with the lifetimes of 7.9 ?s,24.9 ?s,respectively.Meanwhile,the charge-separated state lifetime of YD-TRC-AEAQ also reached 670 ns.To investigate the relationship between charge-separated state lifetime and photoelectric conversion efficiency,five solid-state single-layer organic solar cells based on YD-TRC,YD-TRC-ABF and YD-TRC-AEAQ as well as the previously reported MTPA-TRC and MTPA-TRC-AEAQ were fabricated.The results of the photovoltaic measurement demonstrated that the photoelectric conversion efficiency(PCE)of YD-TRC-ABF(7.9 ?s,0.73%)with long-lived charge-separated state was higher than the PCE of YD-TRC-AEAQ(670 ns,0.60%)and YD-TRC(670 ns,0.04%)in which the charge-separated lifetimes were shorter.Similarly,the PCE of MTPA-TRC-AEAQ(650 ns,0.77%)was higher than that of MTPA-TRC(80 ns,0.05%).These results reveal that the charge-separated state lifetime has an important impact on the PCE of the single-layer solar cells.In the same D-A configuration,elongated lifetime of the charge-separated state can be beneficial for improving the PCE.In addition,computational results suggested that the strong electron withdrawing cyano group could reduce the HOMO,LUMO energy levels and the energy band gap(Eg).Therefore,MTPA-TRC,which possessed good optical properties,was modified by substituting one or two chlorine of triazine with the cyano group.The structures of the two compounds were confirmed by 1H NMR,IR and mass spectra,and the optical and electrical properties were characterized by UV-visible absorption spectroscopy,steady-state fluorescence spectroscopy and cyclic voltammetry.The experimental results that the LUMO level and Eg were reduced in the cyano-substituted compounds were in agreement with the computational results.