Study On Synthesis And Properties Of Charge-separated Sensitizers Containing Electron-deficient Pyrimidine

Achieving high efficiency as well as high stability in organic solar cells has always been the target of organic photovoltaic research.Inspired by natural synthesis,designing and applying organic photovoltaic molecules with long-lived charge-separated?CS?state can be an effective way to improve the photovoltaic performance and stability of the solar cells.In order to investigate the feasibility of using CS material molecules to enhance the photovoltaic performance of the devices,CS sensitizers MTPA-Pyc and YD-Pyc with CS state in nanosecond timescale were synthesized which possess 4-styryltriphenylamine?MTPA?or 4-styrylindoline?YD?as the donor,pyrimidine cyanoacrylic acid?Pyc?as the acceptor and carboxyl acid as the anchoring group.Comparisons were conducted on the differences of the absorption,electrochemical,photophysical properties and photovoltaic performances in DSSC between the designed CS sensitizers and reference CT sensitizers,in which nanosecond CS state was absent.The results demonstrate that CS sensitizers have improved the internal quantum efficiency?IQE?of the DSSCs by 10-30% due to their higher electron injection efficiency and slower charge recombination rate,showing the superiority of CS sensitizers in enhancing the efficiency of the DSSCs.On this basis,the electron-pushing and electron-pulling units of the donor moiety of the CS sensitizers were modified to elucidate the effect of molecular tuning on the properties of the CS sensitizers so that the effect of CS sensitizers on enhancing the photovoltaic performance of the DSSCs can be maximized.Alkyoxyl groups were introduced into the MTPA part to build sensitizers MoTPA-Pyc and OcTPA-Pyc to investigate the effect of electron-pushing unit tuning on the performance of the device.IQEs of DSSCs were enhanced while the influence of the structural modification on the absorption ability of the device was limited.The combined effects led to a maximum of 14% improvement of photocurrent and efficiency of the DSSCs.To examine the influence of electron-pulling unit modification on the device performance,electron-withdrawing groups cyano benzene and benzotriazole were introduced into the backbone of the CS sensitizers and novel sensitizers MTPAco-Pyc,YDco-Pyc,MTPABT-Pyc and YDBT-Pyc were synthesized.The red-shifted absorption band and elongated CS state lifetime of the sensitizers work together,producing a much higher efficiency of the DSSC of 7.41%,which is 30% higher than that of the unmodified parent sensitizers.In order to maximize the effect of the CS sensitizers on enhancing the efficiency of the DSSCs,the correlation between the photovoltaic performances of the devices and the absorption band wavelength and CS state lifetime were summarized,respectively.In addition,the enhancement of long-wavelength absorption of the CS dye sensitized TiO₂ film due to the intermolecular interaction of the adsorbed sensitizers was investigated.The results reveal that long-wavelength absorption contributes to 20-30% of the total photocurrent,thus effectively improved the JSC and PCE of the DSSCs.