Cette thèse concerne l’étude des photodétecteurs à base de matériauxsemi-conducteurs organiques (OPDs) sensibles à la lumière verte. Ces travaux sedivisent en cinq parties distinctes. Tout d’abord, une recherche bibliographique suiviedes notions fondamentales sur les matériaux et le fonctionnement des dispositifsorganiques est présentée. Ensuite, un travail sur la méthodologie concernant lafabrication de bancs expérimentaux et sur la métrologie garantissant l’exactitude desdonnées expérimentales sont effectués. Les méthodes de fabrication etd’optimisation, notamment le dépôt par sérigraphie, sont également présentées. Lapartie expérimentale concerne l’étude de l’origine du courant d’obscurité dans lesstructures organiques à base des matériaux donneur et accepteur d’électrons, laconception et la caractérisation d’un photodétecteur organique à l’état de l’art dontles performances optoélectroniques sont proches des dispositifs inorganiques baséssur la technologie silicium. Enfin, l’étude des mécanismes de dégradation d’uncapteur organique est présentée mettant en avant le rôle de l’oxygène et l’humidité. / This thesis deals with the study of photodetectors based on organicsemiconductor materials (OPDs) that are sensitive to green light. There are five partsto this study. First, a bibliographic study following the fundamentals of organicmaterials and the working principle of organic photodetectors is presented. Then, anextended study on the methodology and metrology is detailed, which was carried outin order to design and fabricate new optoelectronic instruments that are able tocharacterize organic devices accurately. Fabrication and optimization steps oforganic photodetectors are detailed. The experimental section concerns the study onthe origin of the dark current in organic devices based on electron donor/acceptorsystems. A choice of materials is discussed and a full characterisation of state-of-theartorganic photodetectors is presented in detail. The measured performances wereclose to the those of inorganic sensors based on silicon technology. Finally, a studyof degradation mechanisms is presented which highlights the role of oxygen andmoisture.

Organic semiconductor technology has gained attention in both the sensor and display markets due to its low cost and simple fabrication techniques. The ability to fabricate organic semiconductor devices such as photodetectors and transistors on a flexible, lightweight substrate makes them less fragile and ideal candidates for portable large-area imaging applications. The use of organic semiconductor technology in large-area medical imaging can bring about a new generation of flexible and lightweight indirect X-ray imagers. These imagers are immune to mechanical shock and should be ideal for portable intraoral X-ray radiology. In order to realize these organic flexible imagers and their use in large-area medical imaging, many challenges associated with the device performance and fabrication need to be overcome. Among these challenges, one of the greatest is to improve the dark current performance of the organic semiconductor photodetectors (key for imager performance) with a high-photo to-dark current ratio. Low dark current is needed to improve the sensitivity of the imager, whereas a large photo-to-dark current ratio reduces noise in the extracted image. Numerous techniques have been reported to improve the dark current performance in vertical organic photodetector design; however, lateral photodetectors still lack research attention. This thesis presents a lateral multilayer photodetector design and a simplified technique to improve the dark current performance of lateral organic semiconductor photodetectors. Our technique allows us to apply a large bias voltage while maintaining a low dark current, high photo-to-dark current ratio, and improves detector speed; thus, the overall sensitivity of the detector is improved. We further show the integration of an organic photodetector with an organic backplane readout circuit to form a flexible large-area imager. This imager can be used for large-area digital imaging applications such as in medical radiology.

Solution-processed lead sulfide quantum dots (PbS QDs) are an excellent candidate for photodetector applications because they exhibit broadband absorption, a wide range of tuneable bandgaps, high stability in air, and mechanical flexibility. However, a crucial criterion for the fabrication of high-performance photodetectors is the selection of the ligands, which can facilitate charge carrier transport between the PbS QDs and passivate the surface defects. In this work, the authors have studied the effect of traps on the performance of PbS QD photodetectors that are fabricated using different types of ligands, using intensity-dependent photoresponse dynamics. The best devices with lead halide ligands show a dark current density of 5 × 10−9 A cm−2 at −0.2 V, which is one of the lowest values reported thus far for solution-processed PbS QD-based photodetectors. Moreover, these devices show a high linear dynamic range (≈90 dB) and high detectivity (>1013 Jones), in addition to an f-3 dB of greater than 100 kHz without the application of an external voltage bias at a wavelength of 784 nm. These results suggest that with an appropriate selection of ligands, solution-processed photodetectors with a lower density of traps and a better device performance can be fabricated.