The true structure of alternating conjugated polymers – the state-of-the-art materials for a number of organic electronics technologies – often deviates from the idealized picture but this gets relatively limited attention. Here, we quantify the amount of homocoupling defects resulting from Stille polymerization and shed new light on the actual distribution of these structural defects in a prototype polymer material. Further, when compared to a homocoupling-free variant, these defects hinder fullerene intercalation, with a clear implication on charge-transfer absorption. This demonstrates that molecular defects may (strongly) impact polymer and blend properties and calls for increased attention for defect-free materials.
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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