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Schematic structure of the fabricated OLED cells. The thickness of the protein layer (Cyt.C, BSA, etc.) is typically . The active area size of the device is .
AFM images of the substrate and BSA discontinuous films. (a) PEDOT-PSS surface coating ITO/glass. (b) BSA molecules microcontact printed with a flat stamp on (a). Measured height of the structures is . The same gray scale is applied for (a) and (b). (c) BSA-FITC printed twice on silicon substrate with line-and-space patterned stamps. The same structure as in (b) is observed. Two layers of lines (edges are indicated by dashed arrows) cross in the lower-left region.
EL pattern reflecting stamped BSA layers. (a) Line-and-space pattern of 25 and . BSA molecules are stamped on the wider lines (marked by text and arrows), where the light emission is suppressed. (b) The same stamping process was repeated but at a different angle, so that the density of BSA increased at the crossover areas.
Current density (solid lines) and luminance (dashed lines) of OLED cells as a function of applied voltages. A cell with BSA layer shows less current (∎) and less light (◻) than the reference cell (no added layer and ▴ and ▵ for current density and luminance, respectively). A cell with Cyt.C layer shows larger current (●, data divided by 10) and less light (엯) than the reference. Data of reference and Cyt.C were taken from the cells made on the same substrate. Performance varied considerably, for example, a cell with BSA from another fabrication lot showed a doubling of the luminance.
Efficiency is defined as a ratio of luminance and input current (A). BSA (◻), Cyt.C (●), and reference (no interlayer, ▴).
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