Low-Power Monolithically Stacked Organic Photodiode-Blocking Diode Imager by Turn-On Voltage Engineering

Multiplexing the signal readout from the organic photodetector matrix is essential for high-resolution and large-area imaging applications. This endeavor can be realized by pixels containing photodiodes and switching elements, such as transistors or blocking diodes. The use of blocking diodes is beneficial for simpler fabrication and fewer wires than transistors. However, imagers with blocking diodes can always require additional voltage to turn off the unselected lines, which causes high standby power and increased complexity of the readout circuit. In this study, low standby power organic imagers are realized that are suitable for wearable optical imaging applications in which resources for power and readout circuits are limited. Pixels with a vertical stack of organic photodiodes and blocking diode layers are investigated. By increasing the built-in potential of blocking diodes, the turn-on voltage of the monolithically stacked photodiode-blocking diode device can be adjusted to enable its turn-off at 0 V. This leads to a three-orders-of-magnitude reduction of the current of pixels at 0 V. With these pixels, imagers based on organic photodiode-blocking diode stack devices are demonstrated with improved image quality and substantially reduced crosstalk current, while operating at zero standby power.