Multilayers photocurrent measurements

As discussed in section 2.2, a mixture of AMP and AA showed two solid condensed phases above and below about 30 mN m- [5,10]. A loosely stacked structure of two porphyrins was proposed for LB films prepared at higher surface pressures than 30 mNmr1, which was caused by squeezing-out of a monomolecular structure formed at lower surface pressure [5,10]. In this section, photoelectric characteristics of LB films containing AMP and AA deposited at two solid condensed phases will be discussed in relation to multilayer structure and the anisotropic intermolecular tunneling rates [87]. Seven monolayers of 1 5 or 1 10 mixture of AMP and AA were deposited at 20 and 50 mN m-1 on an ITO plate at 18 °C to form stable Y-type LB films. Aluminum was vacuum evaporated onto LB films as sandwich-type electrodes at 10-6 Torr. Steady photocurrents were measured in a similar manner as mentioned above. 

The photocurrent generated by a Chi a multilayer in contact with an aqueous electrolyte without any added redox agents has been measured as a function of pH of the solution (67). 

Lateral photoconductivity spectra and photofield electron emission of multilayer Ge/Si heterostructures with Ge quantum dots were studied at 77 and 300 K. Measurements of lateral photoconductivity spectra at 77 K showed the presence of localized states in the potential well. The photocurrent with limiting energies of 0.3 eV and 0.33 eV can be attributed to electron transitions from localized to delocalized states. A correlation between the regularities of the photoconductivity and photofield emission from such systems was revealed. 

In the ZAHNER controlled intensity modulated photocurrent spectroscopy (CIMPS) system, the light source and the cells are aligned on an optical track. Switching between the reference and the measurement cell is automatic. A close-up of the measurement cell is shown in Figure 15.41, set up for a study of a multilayer organic solar cell model system, shown schematically on the left side. In the PECC-2 cell shown, the reference electrode is Ag/AgCl and the CE is a Pt coil. The cell construction from PTFE or similar polymers allows the use of aggressive and nonaqueous electrolytes. 

---