Theoretical Study Of Solar Cellsensitizers-based On Graphene Quantum Dots-porphyrins/phthalocyanines/phenoxazine-based Nanocomposites

Dye-sensitized solar cell called DSSC,which is a new third generation solar cell.DSSC uses the organic molecules dye to absorb the sunlight and convert the solar energy into electric energy.DSSC not only has the advantages of low cost,simple manufacturing process,abundant raw materials,and has high photoelectric conversion efficiency and good thermal stability close attention by the countries all over the world,many scientific research institutions and organizations.How to improve the photoelectric conversion efficiency of DSSC is the hotspot of research.The photosensitizer can absorb the sun light and cause the initial reaction of the electron,which is the core part of the DSSC.Finding and developing a good dye-sensitizer is of great significance for the development and market application of DSSC.As sensitizer,porphyrin has been reported by research teams,but the light absorption of porphyrin in the wavelength range of 400~600 nm is poor,in order to improve the optical absorption properties of porphyrin,nanocompositesof graphene quantum dots(GQD)-tetraphenylporphyrin(TPP)is constructed.The density functional theory(DFT)and time dependent density functional theory(TDDFT)were used to study the GQD-TPP nanocomposites as sensitizer.First,GQD-TPP nanocomposites were optimized,the energy stability of the obtained structures was confirmed by frequency analysis.The feasibility of nanocomposites as sensitizers was verified by verifying the spatial separation and charge level relationship of the charge.The optical properties of the nanocomposites were calculated by TDDFT,and the obvious enhancement of optical absorption was observed in the nanocomposites.It is found that GQD-3TPPs has obvious spatial separation of charge,proper molecular orbital energy level and good electron transfer driving force.It can be used as a favorable candidate material for sensitizer.Then GQD-phthalocyanine(Pc),GQD-tetrabenzoporphyrin(TBP),GQD-tetrabenzotriazaporphyrins(TBTAP),GQD-cis-tetrabenzodiazaporphyrins(TBDAP),GQD-tetrabenzomonoazaporphyrins(TBMAP)nanocompositeswere studied.First,nanocomposites were optimized and the energy stability of the structure was determined by harmonic frequency analysis.Secondly,the charge space separation,electron transfer,molecular orbital energy level and light absorption properties of nanocomposites are studied.The results showed that all the nanocomposites enhanced significantly in the visible range,and their molecular orbital energy levels all met the requirements of sensitizer.However,only twonanocomposites show obvious space separation charge.The results indicate that GQD-Pc and GQD-Cu-TBP have suitable molecular orbital energy levels and electron transfer driving force,and low electron and hole recombination rate,which is the most favorable candidate sensitizer.Based on DFT and TDDFT,the nanocomposites of graphene quantum dots(GQD1,GQD2,GQD3,GQD4)and phenoxazine dyes(POXB,POXP)were studied.The energy stability of nanocomposites was confirmed by harmonic frequency analysis.Feasibility of nanocomposites as sensitizers is confirmed by the study of space separation and the study of molecular orbital energy levels.The results show that the optical absorption of all nanocomposites is obviously enhanced in the range of visible light,and the energy level relationship is satisfied.GQD4-POXB in addition to meet the requirements of sensitizer,showed a clear separation of space charge,can be as sensitizers.These findings contribute to the design nanocomposites sensitizer to improve the light absorption.