SWIR QLED
SWIR QLED
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Shortwave Infrared
Shortwave Infrared
The Shortwave Infrared (SWIR) region occupies the spectrum band typically spanning from approximately 1µm to 3µm, positioned between the near-infrared (NIR) and mid-infrared (MWIR) regions. Thi sparticular spectrum has many modern applications.
LED working principle
LED working principle
Light-Emitting Diodes operate through the injection of electrons and holes from opposite electrodes under an applied bias. Charge carriers travel through the electron transport layer (ETL) and hole transport layer (HTL) into the central emission layer (EML), where they recombine radiatively to generate photons.
Proper energy band alignment between functional layers is crucial for achieving balanced charge injection into the emission layer and preventing carrier overflow. Large energy barriers can lead to high series resistance, severe charge imbalance, and non-radiative recombination losses, making interface tuning essential for high external quantum efficiency (EQE).
Ultimately, the External Quantum Efficiency is governed by the product of three core efficiency terms:
Photoluminescence Quantum Yield (PLQY): Determines the intrinsic radiative efficiency of the emission layer.
Injection Efficiency: Heavily dictated by proper band alignment to ensure balanced electron and hole transport.
Extraction Efficiency: Governs how effectively generated photons escape the device structure.
To optimise these interfaces and achieve ideal energy matching, a diverse range of both organic and inorganic charge transport layers (CTLs) are available to choose from during device engineering. The appropriate CTL is chosen not only based on the optimal band alignment but also the processing conditions. The idea is to maximise the injection efficiency and reduce or inhibit any non-radiative efficiency within the CTLs.
By definition QLEDs consist of QDs, known for their high PLQY, as active layer for emitting light. While materials determine the PLQY and functional layers determine the injection efficiency, the optical properties (n, refractive index and k, absorption coefficient) of same layers also determine the extraction efficiency of the emitted light. Depending the direction of emission, we can clarrify the QLEDs into bottom emission and top emission. Most of the lab scale QLEDs studied are bottom emitting QLEDs due to their ease in fabrication. However, commercially top emission structures are favourable due to their integration into CMOS.
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