Choi Kyoung Soon, Park Yensil, Kim Soo Young
School of Chemical Engineering and Materials Science, Chung-Ang University, Seoul 156-756, Korea.
J Nanosci Nanotechnol. 2013 May;13(5):3282-7. doi: 10.1166/jnn.2013.7265.
A comparison was performed between the use of graphene oxide (GO) and reduced graphene oxide (rGO) as a hole extraction layer (HEL) in organic photovoltaic (OPV) cells with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester. Hydrazine hydrate (HYD) and the thermal method (Thermal) were adopted to change the GO to rGO. The GO HEL was deposited on an indium tin oxide electrode by spin coating, followed by the reduction process to form the rGO HELs. The success of the reduction processes was confirmed by X-ray diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, transmittance, and 2-point probe method. The OPV cell with the GO (-3 nm) HEL exhibits an increased power conversion efficiency (PCE) as high as 2.5% under 100 mW/cm2 illumination under air mass conditions, which is higher than that of the OPV cell without HEL, viz. 1.78%. However, the PCE of the OPV cell with rGO HEL is not high as the values of 1.8% for the HYD-rGO and 1.9% for the Thermal-rGO. The ultraviolet photoemission spectroscopy results showed that the work function of GO was 4.7 eV, but those of HYD-rGO and Thermal-rGO were 4.2 eV and 4.5 eV, respectively. Therefore, it is considered that GO is adequate to extract the holes from the active layer, but HYD-rGO and Thermal-rGO are not appropriate to use as HELs in OPV cells from the viewpoint of the energy alignment.
在聚（3-己基噻吩）：苯基-C61-丁酸甲酯的有机光伏（OPV）电池中，对氧化石墨烯（GO）和还原氧化石墨烯（rGO）作为空穴提取层（HEL）的使用情况进行了比较。采用水合肼（HYD）和热法（Thermal）将GO转变为rGO。通过旋涂将GO HEL沉积在氧化铟锡电极上，随后进行还原过程以形成rGO HEL。通过X射线衍射、拉曼光谱、X射线光电子能谱、透射率和两点探针法证实了还原过程的成功。具有GO（-3 nm）HEL的OPV电池在空气质量条件下100 mW/cm2光照下表现出高达2.5%的功率转换效率（PCE），高于没有HEL的OPV电池，即1.78%。然而，具有rGO HEL的OPV电池的PCE不高，HYD-rGO为1.8%，Thermal-rGO为1.9%。紫外光电子能谱结果表明，GO的功函数为4.7 eV，但HYD-rGO和Thermal-rGO的功函数分别为4.2 eV和4.5 eV。因此，从能量对准的角度来看，认为GO足以从活性层中提取空穴，但HYD-rGO和Thermal-rGO不适用于OPV电池中的HEL。
