Charge generation layers

The chapter is organized as follows the second section will discuss the photophysics of conjugated polymer/fullerene composites as a standard model for a charge-generating layer in plastic solar cells. Pristine polymer devices will be discussed in the third section while bilayer and interpenetrating network devices are presented in Sections 4 and 5. Section 6 contains some remarks on large area plastic solar cells and Section 7 conclusions. 

Markham JPJ, Anthopoulos TD, Samuel IDW, Richards GJ, Bum PL, Im C, Bassler H (2002) Nondispersive hole transport in a spin-coated dendrimer film measured by the charge-generation-layer time-of-flight method. Appl Phys Lett 81 3266... 

Laquai F, Wegner G, frn C, Bassler H, Heun 8 (2006) Comparative study of frole transport in polyspirobifluorene polymers measured by the charge-generation layer time-of-flight technique. J Appl Phys 99 023712... 

Others have noted that even within a given class of compounds, correlations between the photoinjection efficiencies and oxidation potentials are complex and depend on the charge-generation layer as well (Murayama et al., 1988). 

Hole Transport in PMPS. In the experiments with layered structures (20) and visible excitation (to which PMPS is transparent), transient currents were observed only when the top electrode was negatively biased with respect to the substrate. The substrate was composed of a visible photoconductor (charge generation layer) overcoated aluminum ground plane. When the polymer top surface was directly (intrinsically) photoexcited with pulsed 337-nm excitation, current transit pulses were observed only when the top electrode was positively biased. Therefore, under the experimental conditions described, only hole transient transport could be directly observed. Transit pulses were nondispersive over a wide range of temperature. Figure 14 illustrates the relative increase in dispersion with decreasing temperature. In addition, no evidence for anomalous thickness dependence at the transit time was obtained, even at the lowest temperature. 

Charge Transport Layer Charge Generation Layer... 

Semi-Transparent Electrode Blocking Layer Charge Transport Layer Charge Generation Layer -Blocking Layer... 

Figure 15. Experimental arrangement for time-of-flight measurements. One edge of a thin film ( 1 pm total thickness) is optically excited and charge carriers are produced near the surface of the film. If the optical density of the film is insufficient to absorb the bulk of the irradiation in the first 10 % or so of the film, then a separate charge generation layer is used. A current is detected as the charges migrate across the film until all the photogenerated charge reaches the other electrode.

Figure 16. Transient photocurrent signal from a time-of-flight measurement of a photorefractive polymer composite containing 47.5 % electro-optic dye (EHDNPB), 1 % TNF with PVK polymer making up the remainder 21 V was applied across the 100 nm polymer film and a 10 nm thick rhodamine 6G charge generation layer was used. The hole mobility in this material is thus...

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