Tuyển tập các báo cáo nghiên cứu về hóa học được đăng trên tạp chí hóa hoc quốc tế đề tài : Tuning the electronic band structure of PCBM by electron irradiation | Yoo et al. Nanoscale Research Letters 2011 6 545 http content 6 1 545 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Tuning the electronic band structure of PCBM by electron irradiation Seung Hwa Yoo Jong Min Kum and Sung Oh Cho Abstract Tuning the electronic band structures such as band-edge position and bandgap of organic semiconductors is crucial to maximize the performance of organic photovoltaic devices. We present a simple yet effective electron irradiation approach to tune the band structure of 6 6 -phenyl-C61-butyric acid methyl ester PCBM that is the most widely used organic acceptor material. We have found that the lowest unoccupied molecular orbital LUMO level of PCBM up-shifts toward the vacuum energy level while the highest occupied molecular orbital HOMO level down-shifts when PCBM is electron-irradiated. The shift of the HOMO and the LUMO levels increases as the irradiated electron fluence increases. Accordingly the band-edge position and the bandgap of PCBM can be controlled by adjusting the electron fluence. Characterization of electron-irradiated PCBM reveals that the variation of the band structure is attributed to the molecular structural change of PCBM by electron irradiation. Keywords tunable band structure HOMO LUMO organic semiconductor PCBM electron irradiation Introduction Organic semiconductors such as small molecules 1 2 and conjugated polymers 3 4 are widely used in organic photovoltaic cells 4-6 dye-sensitized solar cells 2 7 organic field-effect transistors 8-10 and organic light-emitting diodes 3 11 . In particular 6 6 -phenyl-C61-butyric acid methyl ester PCBM is a small molecule that is most widely used as an electron acceptor in organic photovoltaic OPV cells 1 . To improve the power conversion efficiency of OPV cells open-circuit voltage Voc of the cells should be increased. The upper limit of the Voc is determined by the energy difference between the highest occupied .
