Role of blend ratio in bulk heterojunction organic retinomorphic sensors

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 1; no. 36; pp. 12998 - 134
• Main Authors: Zhang, Xueqiao, Labram, John G
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 22.09.2022
• Subjects: Butyric acid; Heterojunctions; Luminous intensity; Object motion; Object recognition; Organic semiconductors; Sensors; Visual aspects; Visual fields
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc02048c

Conventional image sensors are designed to digitally reproduce every aspect of the visual field; in general representing brighter regions of a scene as brighter regions in an image. While the benefits of detecting and representing light in this way are obvious, limitations imposed by processing power and frame rate place a cap on the speed at which moving objects can be identified. An emerging alternative strategy is to use sensors which output a signal only in response to changes in light intensity, hence inherently identifying movement by design. These so-called retinomorphic sensors are hoped to outperform conventional sensors for certain tasks, such as identification of moving objects. In this report, the working mechanism of retinomorphic sensors based on organic semiconductors as the active layer is probed. It is observed that the sign of the voltage signal is changed when electrode connections are reversed, suggesting our previous description of device behaviour was incomplete. By systematically varying the ratio of poly(3-hexylthiophene-2,5-diyl) (P3HT) to phenyl-C 61 -butyric acid methyl (PCBM) in the absorption layer, a maximum performance was observed when the ratio was 1 : 2 P3HT : PCBM, while pure P3HT and pure PCBM exhibited very weak signals. A mixture of P3HT and PCBM was found to yield a larger signal than pure P3HT or pure PCBM in retinomorphic sensors.