Position Sensing by Transient Photocurrents of Organic Photodiodes

Organic photodiodes not only show good quantum efficiencies in the visible range and fast pulse responses down to the nanosecond regime, but also allow for arbitrary shapes of the active area. The usual device structure is a thin organic semiconductor absorber sandwiched between two electrodes of which one is transparent. This leads to a high device capacitance for large area devices. In conjunction with a high electrode resistance, the transient photocurrent response under localized pulse excitation becomes dependent on the position. We make use of this effect and demonstrate a method for position sensing in oblong organic photodiodes achieving a standard deviation in the position measurement of less than 100 mu m at the edges and 12 mu m at the center of an 8000-mu m long device.