A technology that allows organic photodiodes (OPDs) to detect objects in strong light by adding small molecules has been developed. OPDs are optical sensors that detect color and brightness by converting light energy into electrical energy. Originally, objects could not be easily detected when receiving strong light such as sunlight.
A research team led by Professor Chung Dae-sung (CE) and Dr. Kang Min-kyun (CE) succeeded in enhancing the performance of OPDs by synthesizing molecular switches. These research results were published in Advanced Materials.
Unlike inorganic semiconductors, organic semiconductors that have a low charge mobility create a limited amount of electrical energy even when the intensity of light increases. Thus, studies have been conducted to create more electrical energy with stronger light by increasing the charge mobility of organic semiconductors. However, in this process, their properties change, resulting in less accuracy in color detection.
The research team focused on a “molecular switch” with different properties when they are exposed to light or stimulated. As a result of synthesizing a molecular switch and adding it to the organic semiconductor layer of a photodiode, it was possible for OPDs to accurately detect colors while showing excellent detectivity. Specifically, the advantage is that it can be applied regardless of the type of organic semiconductor in the photoactive layer.
A typical molecular switch is converted to the semiconductor when receiving ultraviolet light from the initial state and is returned to the initial state when receiving visible light. However, based on the fact that the distribution of the initial state and the semiconductor state changes according to the intensity of white light, the research team implemented a molecular switch that changes its state autonomously depending on the intensity of incident light.
OPDs, which are components of image sensors, can be used for cameras and biometric sensors including iris and fingerprints, and optical communication. OPDs increase the performance of autonomous vehicles and drone sensors that are frequently exposed to sunlight by allowing objects to be detected even in strong light.
Prof. Chung said, “We proposed a structure of a photodiode that changes its driving mechanism on its own according to the intensity of light,” adding, “It is meaningful that a molecular switch was used as a material that induces the change in the driving mechanism on its own.”
Meanwhile, this study was conducted with the support of Samsung Electronics’ Samsung Science & Technology Foundation Center.