Toward a better understanding of the doping mechanism involved in Mo(tfd-COCF3)3_3)_3 doped PBDTTT-c

In this study, we aim to improve our understanding of the doping mechanism involved in the polymer PBDTTT-c doped with(Mo(tfd-COCF3)3. We follow the evolution of the hole density with dopant concentration to highlight the limits of organic semiconductor doping. To enable the use of doping to enhance the performance of organic electronic devices, doping efficiency must be understood and improved. We report here a study using complementary optical and electrical characterization techniques, which sheds some light on the origin of this limited doping efficiency at high dopant concentration. Two doping mechanisms are considered, the direct charge transfer (DCT) and the charge transfer complex (CTC). We discuss the validity of the model involved as well as its impact on the doping efficiency.Comment: Accepted manuscript, J. Appl. Phy

P-doped organic semiconductor: Potential replacement for PEDOT:PSS in organic photodetectors

In this work, we present an alternative to the use of PEDOT:PSS as hole transport and electron blocking layers in organic photodetectors processed by solution. As Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is known to be sensitive to humidity, oxygen, and UV, removing this layer is essential for lifetime improvements. As a first step to achieving this goal, we need to find an alternative layer that fulfills the same role in order to obtain a working diode with similar or better performance. As a replacement, a layer of poly[(4,8-bis-(2-ethylhexyloxy)-benzo(1,2-b:4,5-b′)dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene-)-2-6-diyl)] (PBDTTT-c) p-doped with the dopant tris-[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd-COCF3)3) is used. This p-doped layer effectively lowers the hole injection barrier, and the low electron affinity of the polymer prevents the injection of electrons into the active layer. We show similar device performance under light and the improvements of detection performance with the doped layer in comparison with PEDOT:PSS, leading to a detectivity of 1.9 � 1013 cm (Hz)1/2 (W)-1, competitive with silicon diodes used in imaging applications. Moreover, contrary to PEDOT:PSS, no localization of the p-doped layer is needed, leading to a diode active area defined by the patterned electrodes

Photocurrent deviation from linearity in an organic photodetector due to limited hole transport layer conductivity

International audienceIt has been demonstrated that p-doped polymer layers are a convenient replacement as hole transport layer (HTL) for the widely used Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), yielding comparable photodetection performances at low light intensities. In this work, we aim to evaluate the response of organic photodetectors (OPDs) with increasing light intensity when p-doped PBDTTT-c is used as HTL. Photocurrent linearity measurements are performed on devices processed with both PEDOT:PSS and p-doped PBDTTT-c to better determine the role of the HTL. We show a deviation of the photocurrent from linearity for light intensities above 10-3 W/cm2 at 0 V applied bias due to distinct mechanisms depending on the HTL material. While space charge limited photocurrent (SCLP) explains the non-linearity at high light intensity for the device processed with PEDOT:PSS, bimolecular recombination is responsible for the loss in linearity when p-doped PBDTTT-c is used as HTL. The replacement of PEDOT:PSS by p-doped PBDTTT-c, which is 6 orders of magnitude less conductive, induces Langevin recombination, causing photocurrent non-linearity. Therefore, this study emphasizes the need for highly conductive transport layers when photodetection applications are targeted, and motivates further improvements in organic semiconductor doping

Hyperthermic intraperitoneal chemotherapy in ovarian cancer: An update

International audienceIn the treatment of advanced-stage epithelial ovarian cancer (EOC)-associated surgery and chemotherapy with intravenous platinum/taxane-based therapy most patients had early or late recurrence. Prevention of progression and recurrence is a major objective for the management of EOC. Recently, many clinical studies have evaluated the strategy with hyperthermic intraoperative intraperitoneal (IP) drug delivery. This is an update of hyperthermic intraoperative intraperitoneal chemotherapy (HIPEC) in EOC and a view for future strategies. Until recently studies on HIPEC in patients with EOC were mostly retrospective and heterogeneous. Thanks to recent clinical trials, it is reasonable to conclude that surgical cytoreduction and HIPEC is an interesting approach in the management of EOC without increasing morbidity. © 2020 Walter de Gruyter GmbH, Berlin/Boston

Current status and challenges of the modeling of organic photodiodes and solar cells

International audienceProgress in the modeling of charge transport in solution processed solar cells and photodiodes is reviewed. Through several examples involving modeling and original experiments, the role of intentional doping, structural defects, and oxygen contamination are discussed

Photonic crystal patterning of luminescent sol-gel films for light extraction

International audienceStructured luminescent thin films are investigated in the context of improved light extraction of phosphors for solid-state-lighting applications. Thin films composed of a sol-gel titania matrix doped with europium chelates are studied as a model system. These films, patterned with a square photonic lattice by soft nanoimprint lithography, are characterized by angle-resolved fluorescence. Modeling of this simple technique is shown to fit well the experimental data, revealing in great detail the guided modes of the film and their extraction parameters. An eightfold extraction enhancement factor of the film emission is measured. To further improve the extraction efficiency, we investigate the role of an additional low-index mesoporous silica underlayer through its influence on the guided modes of different polarizations and their interactions with the photonic crystal. Results obtained on model systems open the way towards the optimization of light-emitting devices, using a strategy of dielectric microstructure engineering using the sol-gel process

On the front and back side quantum efficiency differences in semi-transparent organic solar cells and photodiodes

International audienceThe External Quantum Efficiency (EQE) of semi-transparent Bulk Hetero-Junction (BHJ) organic photodiodes processed in air shows significant differences when measured from the front or back side contacts. This difference was found significantly reduced when decreasing the active layer thickness or by applying a negative bias. This work brings new elements to help understanding this effect, providing a large set of experiments featuring different applied voltages, active layers, process conditions and electron and hole layers. By the mean of detailed electrical simulations, all these measurements have been found consistent with the mechanisms of irreversible photo-oxidation, modeled as deep trap states (and not as p type doping). The EQE measurement from front and back side is thus a simple and efficient way of monitoring the presence and amplitude of oxygen contamination in BHJ organic solar cells and photodiodes