Cathode buffer layer

Mix liquid samples in a ratio of 3 vol. of sample to 1 vol. of buffer (fourfold), dissolve solid samples in 1 4 diluted buffer G, heat to 80 °C for 10 min, and add the samples to form a layer below the cathode buffer in the sample pockets of the gel. 

The cathode is typically a low-to-medium workfunction () metal such as Ca (0 = 2.87 eV), A1 ( = 4.3 eV),15 or Mgo.gAgo.i (for Mg,

beam evaporation. However, in case of A1 or Ca, addition of an appropriate buffer layer between the top organic layer and the metal cathode improves the device performance considerably. This issue is discussed in some detail in Sec. 1.5.8 below. 

Other approaches have involved reduction of interchain interaction either by cross-linking the polymers using vinyl endgroups [ 71 ] or by attaching bulky groups, e.g., dendrimers [72,73] or silsesquioxanes [74,75], as end- or side-groups. There is evidence that reduction of fluorene by calcium cathodes is implicated in the formation of ketone defects during LED operation, and this can be suppressed by introduction of a buffer layer between the polymer and the cathode [76]. 

Fig. 11.17 The energy-level diagram for the two-layer system CuPc/Cgo (left) between an ITO anode and an aluminium cathode and for the mixed system CuPciCgo between an ITO anode with a PEDOT PSS buffer layer, and an aluminium cathode (right). The level scheme is shown for the case that the layers are not yet in contact. After making contact, the Fermi levels equalise, so that the HOMOs and the LUMOs are bent in such a way that the electrons drift...

A hybrid HBETL material composed of polymerized fiiUerene derivative (C-PCBSD, Figure 78) and ZnO was introduced by Hsieh et al Inverted P3HT/[60]PCBM organic solar cells with ITO cathode covered with ZnO buffer layer yielded power conversion efficiency of 3.5%. On the contrary, devices comprising hybrid HBETL represented by ZnO/poly-C-PCBSD junction yielded much higher power conversion efficiency of 4.4% mainly due to the increased photocurrent density (/sc = 12.8 mA cm )... 

Figure 75 The formation of vertically segregated P3HT + PCBM/PEG system where PEG behaves as a buffer layer modifying aluminum cathode/active layer interface. (Reproduced from Ref. 225. Royal Society of Chemistry, 2009.)...

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