Charge carrier transport junction barrier

A high barrier in the conduction band due to unfavorable band line-up or interface charge at the buffer/TCO junction may impede the majority carrier transport at this nn-junction. There are no indications for a significant barrier in standard cells but it has been made responsible for the poor performance of certain cells with alternative Cd-free buffer layers [9]. 

Figure 2 Schematic illustration of the (transport) properties of the blood-brain barrier. Shown is the influence of astrocyte endfeet at the brain capillary endothelial cell. This cell has narrow tight junctions, low pinocytotic activity, many mitochondria, and luminal anionic sites that hinder the transport of negatively charged compounds. Passive hydrophilic transport occurs via paracellular diffusion (tight junctions), whereas passive lipophilic transport is a transcytotic process. Adsorptive-, receptor-, and carrier-mediated transport has been indicated. The metabolic properties of the BBB are illustrated by the various enzymes at the BBB [from (157), with permission].

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