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

Abstract

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.

Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current

“…For high‐resolution and large‐area imaging applications, so‐called active‐matrix addressing is typically used. Switching elements are typically introduced in the form of thin‐film transistors (TFTs), although the use of blocking diodes has also been recently proposed …”

“…The negative bias voltage applied to OPD arrays when integrated with a TFT matrix ensures that the diode remains sufficiently charged, and effectively implies that the readout charge is linearly proportional to the amount of collected photocarriers. The reverse bias also increases the response speed of the diode, and often the collection efficiency, i.e., the extraction of photogenerated charge carriers at the contacts.…”

The Bulk Heterojunction in Organic Photovoltaic, Photodetector, and Photocatalytic Applications

“…OPD technologies, based on organic photodiodes, have, to date, not yet gained the same level of scientific attention. [212][213][214][215][216][217][218] Similar to the photophysical processes of OPVs, the control of the BHJ morphology and excitonic nature of organic materials is key to the development of successful OPD devices. The blending of donor and acceptor materials in a BHJ architecture is widely used in OPD to enhance exciton dissociation at the D:A interface and therefore improve charge extraction via the bicontinuous percolating network.…”

A Highly Responsive Organic Image Sensor Based on a Two‐Terminal Organic Photodetector with Photomultiplication

“…The rectifying layers alone formed an organic blocking diode with a good rectification of 1.51 × 10 3 at +2/−2 V (Figure S6, Supporting Information). The rectifying layers help the rectification of an organic image sensor pixel, which enables multiplexing and eliminating unwanted electrical crosstalk in an organic image sensor matrix . The blocking diode possesses a turn‐on voltage of ≈1.5 V. Therefore, the drive voltage of the photodetector with rectifying layers also shows a similar amount of voltage shift toward negative voltage values.…”