Abstract
Near-infrared (NIR) proximity sensor combines a polymer light emitting diode (PLED) and a polymer photo detector ( PPD). It is easy for organic materials to be applied in large-area and flexible substrate due to their mechanic property, and they have potential for low-cost fabrication process . As a result, organic materials must be properly used to the skin of robots. If the skin of robots can be covered with a high density array of proximity sensors, it will be able to move in unstructured and unpredictable environments without collisions. For proximity sensors, there are many advantages to operate in the NIR range, such as low dispersion, low loss, low eye-sensing and low environment interference. The NIR emission is obtained by adding a color conversion film of phosphors to a green-emitting Green-B LED, and then through the visible light filter to be formed. Measuring the conversion efficiency from photoluminescence is over 20% . On the other hand, PPD with voltage-adjustable photoresponse from visible to NIR range (650nm~900nm). Poly(3-hexylthiophene) and (6,6)-phenyl-C61- butyric acid methyl ester (PCBM) blend is used as the active layer. The PPD detection photocurrent will be transfer to voltage signal by means of current to voltage operation amplifier, and then be presented in the computer by Data Acquisition card. To decrease the current for driving PLED, we use four PLED and one PPD. When the PLED is biased at 7 V and the PPD is biased at -20V, PPD can detect the net photocurrent over 100nA for white paper under ambient indoor lighting and detection distance 10 cm. Finally, we can obviously identify the difference between object-far and object-close voltage signals, and then we come to array NIR proximity sensor that can detect the location of the object immediately.