Light- and touch-point localization using flexible large area organic photodiodes and elastomer waveguides
Sprache des Vortragstitels:
SPIE Europe Optics + Optoelectronics, Prague, Czech Republic
Sprache des Tagungstitel:
A large area photodiode consisting of zinc-phtalocyanine and fullerene C60 sandwiched between two bad conductive electrodes of semitransparent aluminum and Poly(ethylenedioxythiophenes) Polystyrenesulfonate (PEDOT:PSS), respectively, can be used as a two dimensional position sensitive device for detecting light spots or mechanical pressure. The current generated in the photodiode by a laser diode (532nm, 0.8mW) drops over the resistive electrodes to the edges of the device and depends on the distance between the excitation and the point where the resistive electrode is connected with the outer circuit.
A simple mathematical model was developed to evaluate the incoming signals, where the signal ratio log(I1/I2) taken from two opposite edges of one electrode is direct proportional to the x-coordinate and log(I3/I4) of the other electrode to the y-coordinate of the device. Using this model, a change in magnitude of the generated current due to inhomogenities in the charge generation as well as variation of the laser intensity has no effect and can then be neglected.
The range of signal ratios of a channel depends strongly on the sheet resistance of the respective electrodes. Furthermore, an offset of the signal ratio can be generated using a simple addition of a resistor in the outer circuit of a channel. Finally, due to the complex architecture of capacitances and resistances, the performance of the device can be strongly influenced by changing the modulation frequency of the excitation light. The device behaves as if the sheet resistance of the electrodes increases strongly with the applied frequency, leading finally to a resonance in the signal ratio and then a decrease. Using the characteristics described above, the device can be tuned for all kinds of applications.