Patric Büchele

Imaging with organic and hybrid photodetectors

Organic semiconductors provide exiting new opportunities for the realization of flat panel image sensors as they can be processed from the solution phase on large areas at low cost. In particular the high charge separation efficiency obtained in a bulk heterojunction (BHJ) enables the realization of organic photodiodes (OPDs). The spectral sensitivity of OPDs can be tailored to cover wavelengths ranging from the visible to the near infrared region. These sensitivities match perfectly to a variety of X-ray scintillators enabling a further improvement in the sensitivity range. In combination with an amorphous silicon (a-Si) thin film transistor (TFT) backplane technology, visible, near infrared (NIR) and X-ray image sensors have been realized. Thin film OPDs have been used in combination with a cesium iodide (CsI) scintillator in a traditional stacked geometry, proofing state-of-the art performance. Even more, it is possible to blend X-ray absorbing particles directly into the organic semiconductor thereby enabling quasi-direct X-ray converters with the promise to achieve a modulation transfer function (MTF) that is as high as in direct converting materials such as amorphous Selenium.

Silicon micro venturi nozzles for cost-efficient spray coating of thin organic P3HT/PCBM layers

Improvements on spray coating are of particular interest to different fields of technology as it is a scalable deposition method and processing from solutions offer various application possibilities outside of typical facilities. When it comes to the deposition of expensive and film-forming media such as organic semiconductors, consumption and nozzle cleaning issues are of particular importance. We demonstrate the simple steps to design and fabricate micro venturi nozzles for economical spray coating with a consumption as low as 30–50 µl min−1. For spray coating an active area of 25 cm2 a 2.45–4.01 fold coating efficiency is observed compared to a conventional airbrush nozzle set. The electrical characterization of first diodes sprayed with an active layer thickness of ~750 nm using a single micronozzle at a coating speed of 1.7 cm2 min−1 reveals a good external quantum efficiency of 72.9% at 532 nm and a dark current of ~7.4 10−5 mA cm−2, both measured at −2 V. Furthermore, the high resistance of the micronozzles against solvents and most acids is provided through realization in a silicon wafer with silicon dioxide encapsulation, therefore allowing easy and effective cleaning.