The current state-of-the-art infrared (IR) systems use inorganic semiconductors for so-called photonic detection in the near (few μm) and mid-IR (10’s of μm) range and switch to thermal detection systems such as bolometers for the large wavelength regimes (up to mm range). In order to lower the cost of IR detectors, much effort is put into designing low-gap polymers or molecules for organic photo-detectors, but their detection range is currently still limited to 1500-1600 nm wavelengths, with modest detectivities in comparison to existing inorganic technologies in the short wave infrared (SWIR) range. In this work, we look at the possibility of using organic semiconductors in a bolometric device for infrared detection over an extensive wavelength range, spanning from the SWIR to the mid-IR. We find advantages of using organic materials compared to inorganic materials for the fabrication of bolometers and use theoretical modeling to guide us on which parameters we can use to optimize our devices. We find two key parameters determining the device performance: the polymers’ thermal conductivity and the overall device thickness.
Semiconducting organic polymers are most often synthesized by linking an electron poor and an electron rich (hetero)aromatic building block via a transition metal catalyzed cross-coupling copolymerization. Researchers aiming at exploring applications and fundamental performance limits, for example for organic photovoltaics, organic photodetectors, and organic electrochemical transistors, often assume that the obtained material consists strictly of a perfect repetition of the depicted polymeric repeating unit, whereas this is likely not the case. In this contribution, we demonstrate a synthesis approach to obtain the depicted “perfect” structure of these types of polymers and the influence of material defects on the optoelectronic properties and device performance.
Organic photodetectors (OPDs) with a performance comparable to that of conventional inorganic ones have recently been demonstrated for the visible regime.[1] However, near-infrared photodetection at a high detectivity has been proven to be more challenging and, to date, the true potential of organic semiconductors in this spectral range (800‒2500 nm) remains largely unexplored. We have recently shown that the main factor limiting the specific detectivity ( ) is non-radiative recombination, which is also known to be the main contributor to open-circuit voltage losses in organic photovoltaics.[2] Based on this finding we concluded that OPDs have the potential to be a useful technology up to 2 μm, given that high external quantum efficiencies can be maintained at these low photon energies. To further elaborate on the fundamentals defining these limitations, a next-generation of ‘defect-free’ organic semiconductors is synthesized. This allows us to investigate the influence of material imperfections (end-capping, homocoupling defects, and other impurities) on the material properties and device performance. In this contribution, we give an overview of the synthetic approaches applied and the latest organic semiconductors for high performance NIR OPDs, approaching their intrinsic limits.
[1] N. Li et al., Mater. Sci. Adn Eng., 146, 100643 (2021)
[2] S. Gielen et al., Adv. Mater., 32, 2003818 (2020)
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