Organic photodetectors are lightweight, tunable, and can be integrated with other materials, making them a promising alternative to detectors made with inorganic materials. Organic detectors are also less expensive and simpler to fabricate than their inorganic counterparts. Narrowband infrared (IR) organic photodetectors are highly desirable for sensing, imaging, and spectroscopy applications and for handheld devices. However, most existing strategies for achieving narrowband IR detection depend on spectral filtering using thick films or external filters. These add bulk and introduce strong angular dispersion, causing the color that is being detected to drift. To address these concerns, researchers at the University of Turku designed an organic IR photodiode using polariton technology. The new device demonstrates record-high responsivity, surpassing the performance of previously reported narrowband organic photodiodes in the near-infrared (NIR) region. Konstantinos Daskalakis is an associate professor of materials engineering at the University of Turku and part of the team that developed an ultrathin, organic infrared (IR) photodiode with record-level sensitivity. Courtesy of the University of Turku. By engineering strong exciton-photon coupling into the photodetector, the researchers gave the device’s polariton mode a flattened dispersion that preserved color selectivity across wide viewing angles, while keeping the active layer exceptionally thin, at only 100 nm. Microcavity exciton-polariton modes, which emerge from strong exciton-photon coupling, have been explored as a means to achieve angular dispersion suppression. The researchers used a non-fullerene acceptor, blended with an active material, to establish a clean morphology and efficient charge transport within the device’s compact Fabry-Pérot cavity design. The non-fullerene acceptor allows the device to achieve strong coupling in the NIR spectrum, due to its high oscillator strength in this spectral range. Non-fullerene acceptors provide a versatile platform for expanding the operating wavelength range of an organic photodiode, because their absorption properties can be molecularly tailored to cover both the visible and IR regions. The researchers found the organic IR photodiode’s measured detectivity to be competitive with leading organic approaches. The polariton photodiode exhibited an exceptionally narrow detection band and maintained high responsivity without separate filters. It demonstrated ultrafast responsivity, reaching a high responsivity in the IR region of about 945 to 990 nm. At 965 nm, the researchers recorded a responsivity of 0.23 amperes per watt at 0 volts (0.23 A W-1 at 0 V), which is the highest reported to date. The device showed minimal dispersion across a wide angular acceptance cone of plus-minus 45 degrees (±45°), demonstrating its angle-independent nature. The performance of this photodiode demonstrates that the use of polaritonic effects can lead to substantial improvements in photodetector performance. The device could set a new benchmark for narrowband organic IR photodiodes. “We demonstrate that polaritonic engineering is not only a concept from fundamental physics, but also a practical pathway to solve real device challenges, such as angular color stability and sensitivity in a truly thin architecture,” researcher Ahmed Gaber Abdelmagid said. Ahmed Gaber Abdelmagid is a doctoral researcher of materials engineering at the University of Turku. Courtesy of the University of Turku. The organic IR photodiode could provide the groundwork for the development of high-responsivity, angle-independent polaritonic, optoelectronic devices for applications in imaging, sensing, and spectroscopy and for compact, low-power sensors for medical, environmental, and wearable technologies. By molecularly tuning non-fullerene acceptors, the same polaritonic approach could be extended from the visible into the IR. This would enable lightweight, low-power sensors for phones and wearables, compact spectrometers for point-of-care diagnostics, and energy-efficient modules for autonomous platforms, without the drawbacks of bulky filters or thick absorbers. “By tailoring light-matter interaction inside the cavity, we unlock narrowband infrared detection that fits the needs of compact and wearable systems on a robust polariton platform,” professor Konstantinos Daskalakis said. The research was published in Advanced Optical Materials (www.doi.org/10.1002/adom.202501727).