Near-infrared (NIR) light-emitting devices have recently garnered significant interest for integration in various applications, including photodynamic therapy and component determination, with emission wavelengths ranging from 700 nm to 2500 nm....

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Although organic light-emitting devices (OLEDs) can achieve an internal quantum efficiency (QE) of 100%, their external QE remains limited to less than 40% due to low outcoupling efficiency (OCE). The distribution of excitons is a critical factor in determining OLED OCE, as it affects the coupling to surface plasmon polaritons. Therefore, investigating exciton distribution through experiments is crucial to optimize device structure and enhance OCE. In this study, we propose a probe method to analyze exciton distribution by inserting an ultrathin (∼0.1 nm) near-infrared (NIR) material at a specific position within the emitting layer (EML). With a low excited state energy level, the NIR probe can utilize excitons generated around the specific EML position. By preparing different devices with the NIR probe at various EML positions, we can quantitatively present exciton distribution using the NIR to visible emission ratio. Our results demonstrate that this probe method is effective for investigating exciton distribution in blue, green, and red OLEDs with hole-dominant, electron-dominant, and bipolar transport EMLs, respectively.

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