Photoelectric Properties Of Single-Bonded Fullerene Dimer Derivative Films

The unique properties of fullerene have attracted wide attention due to their unique highly symmetrical structure,physical properties of light sensitivity and broad application prospects.In recent years,fullerene dimers can improve some chemical and physical properties of fullerenes.Therefore,fullerene dimers have become a research hotspot.The single-bonded fullerene dimer(type RC₆₀-C₆₀R)has a direct covalent bond between two fullerene cages.Through the interaction of two adjacent C₆₀ cages,the RC₆₀-C₆₀R structure is expected to show interesting optical and electronic properties.The physical and chemical properties of fullerene dimer derivatives are related to the side-chain groups and lengths,which can produce certain unique optical and electrical properties,making fullerene dimers promising in photoelectronic devices.In order to explore the influence of carbon chain length on the optical and electrical properties of single-bond fullerene dimer derivatives,spin coating method is used to prepare the organic films.The influence of carbon chain length on the spectral properties and photoelectric properties of single-bond fullerene dimer films are studied in detail,and the method to improve the photoluminescence efficiency of the films is further studied.The research content is mainly divided into the following three parts:1.The single-bond fullerene dimer derivatives（C4-C6）are dissolved in 1,2-dichlorobenzene,and the organic film is made by spin coating.The C4-C6 films are characterized by UV-Vis absorption spectrum,voltammetric cycle diagram,Raman spectrum and photoluminescence spectrum.The effect of carbon chain length on the spectral properties of the single-bond fullerene dimer films are studied.The results are as follows:（1）The lowest unoccupied molecular orbital energy levels of the single-bonded fullerene dimer derivatives（C4-C6）which are measured with electrochemical cyclic voltammetry are-3.89 e V,-3.90 e V,and-3.92 e V,respectively.The energy gaps are 2.05e V,2.04 e V,and 2.04 e V.（2）The C4-C6 thin film ultraviolet-visible absorption peaks are located at 264 nm and 444 nm,respectively.（3）The Raman spectra of the single-bonded fullerene dimer derivatives（C4-C6）show similar shapes:Two Raman peaks locate at1377cm^-1 and 1584cm^-1,respectively.（4）There are two obvious peaks in the photoluminescence spectrum of the film.The maximum photoluminescence intensity is at 735 nm（ZPL）,and the secondary peak is at 806 nm（1PL）.At the same time,the results show that the carbon chain length has little effect on the Eg of the single-bond fullerene dimer derivative（C4-C6）,but the intensity of the UV-visible absorption spectrum,Raman spectrum and photoluminescence spectrum of the film has a greater impact and increases with the length of the carbon chain.Among the three kinds of the single-bonded fullerene dimer derivatives,C6 has the best optical properties.2.In order to improve the photoluminescence efficiency of the single-bond fullerene dimer derivatives（C4-C6）,the effects of different substrates（Au,Si）and low temperature on the photoluminescence spectrum of the single-bond fullerene dimer derivatives（C4-C6）films are studied.The study found that:（1）Due to the phenomenon of metal surface enhanced photoluminescence on Au substrate,its photoluminescence intensity is much stronger than that of the single-bond fullerene dimer derivative（C4-C6）film on Si substrate.Under 532 nm laser irradiation with a power density of 32.13 W/cm²,the integrated intensities of photoluminescence spectrum on the Au substrate of the single-bonded fullerene dimer derivative（C4-C6）are 24.91 times,49.45 times and 67.20 times of those on the Si substrate,respectively.（2）When the temperature is 100K,the single-bonded fullerene dimer derivatives（C4-C6）have the strongest photoluminescence intensity.The C4-C6 photoluminescence intensity increased by 92%、90%and 116%,respectively,compared with that at room temperature.At the same time,the substrates and low temperature have no effect on the peak position of its photoluminescence spectrum.According to the experiment,Au substrate and low temperature can improve photoluminescence efficiency of the single-bonded fullerene dimer derivatives,which makes the single-bonded fullerene dimer material a potential luminescent material.3.The effects of carbon chain length on the current-voltage and photoresponse characteristics of the single-bonded fullerene dimer derivatives（C4-C6）thin-film devices have been further investigated.It is worth noting that when the laser power density is the same and the laser wavelength is 405 nm,the photocurrent of the single-bonded fullerene dimer film increases sharply.For the single-bonded fullerene dimer derivative（C4-C6）devices with different side-chain carbon chain lengths,the photocurrent of C4-C6 devices increases 2 and 7 times with the increase of carbon atoms in the ester group from 4 to 5and 6 under the irradiation of 405 nm laser with power density of 0.5 m W/cm².We speculate that as the carbon chain length of the single-bond fullerene dimer derivative increases,its electrical properties and quantum efficiency of light response increase accordingly,but the molecular stability decreases at the same time.The results provide useful reference for further understanding the photoelectric properties of the single-bonded fullerene dimer films,and help to understand the relationship between the photoelectric properties of the single-bonded fullerene dimer films and the length of carbon chain to improve the device performance.