Filterless Wavelength-Selective Printed Organic Photodiodes: Correlating Ink Engineering to Device Performance and Functionality.

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Organic semiconductors combine synthetic tunability of optoelectronic properties with the ability of fabrication from solution with scalable printing techniques. This synergy has made organic photodiodes (OPDs) one of the most promising photodetection technologies in recent years. However, the complex correlations between processing and device performance has so far strongly limited OPDs to live up to their potential. Particularly, functionalities that rely on parameter flexibility, like color selective detection, are lacking behind due to intrinsic challenges resulting from the most common organic bulk-heterojunction (BHJ) material systems. In such BHJ-systems the device spectral range is mainly governed by the absorption of a polymer donor. Conversely, due to its polymeric nature, it also dictates to a great extent the viscoelastic properties of the ink. This interdependence creates a bottleneck for the ink development and spectral flexibility of printed OPDs. In the proposed project, we will investigate the potential of a newly developed concept that overcomes this challenge, by addressing the decoupling of the viscoelastic properties of the ink from the spectral responsivity of the device, lowering fabrication complexity and gaining greater access to the tuning of device spectral responsivity. This is realized by focussing on “passive” polymer donors (or acceptors) (i.e. ideally not contributing to the photocurrent) to define the ink rheology in combination with suitable small-molecule acceptor (or donor) materials which dictate the spectral responsivity of the device. Based on our sucesfull preliminary work, we will select organic material systems outside the scope of sun-light harvesting for fabrication of filterless wavelength-selective OPDs offering high efficiency, large spectral flexibility and low printing complexity. To provide a thorough understanding of the underlying mechanisms, the OPD fabrication will be complemented by advanced spectroscopical and morphological investigations. The resulting know-how will greatly contribute to the understanding of the complex correlations between printing processes, multilayer architectures and device physics. We believe that our approach combined with the use of digital printing techniques, will enable the seamless integration of the developed OPDs into multidevice optical detection systems.