14 research outputs found
Effective Ion Mobility and Long-Term Dark Current of Metal Halide Perovskites with Different Crystallinities and Compositions
Ion transport properties in metal halide perovskite still constitute a subject of intense research because of the evident connection between mobile defects and device performance and operation degradation. In the case of X-ray detectors, dark current level and instability are regarded to be connected to the ion migration upon bias application. Two compositions (MAPbBr3 and MAPbI3) and structures (single- and microcrystalline) are checked by the analysis of long-term dark current evolution. Electronic current increases with time before reaching a steady-state value within a response time (from 104 down to 10âs) that strongly depends on the applied bias. A coupling between electronic transport and ion kinetics exists that ultimately establishes the time scale of electronic current. Effective ion mobility
is extracted for a range of applied electric field Ο. While ion mobility results field-independent in the case of MAPbI3, a clear field enhancement is observed for MAPbBr3 (
), irrespective of the crystallinity. Both perovskite compounds present effective ion mobility in the range of
âââ10â7â10â6âcmâ2âVâ1âsâ1, in accordance with previous analyses. The Ο-dependence of the ion mobility is related to the lower ionic concentration of the bromide compound. Slower migrating defect drift is suppressed in the case of MAPbBr3, in opposition to that observed here for MAPbI3.This work has received funding from the European Union's Horizon 2020 research and innovation program under the Photonics Public Private Partnership (www.photonics21.org) with the project PEROXIS under the grant agreement N° 871336
Mobile Ion-Driven Modulation of Electronic Conductivity Explains Long-Timescale Electrical Response in Lead Iodide Perovskite Thick Pellets
The favorable optoelectronic properties of metal halide perovskites have been used for X- and Îł-ray detection, solar energy, and optoelectronics. Large electronic mobility, reduced recombination losses of the electronâhole pairs, and high sensitivity upon ionizing irradiation have fostered great attention on technological realizations. Nevertheless, the recognized mixed ionic-electronic transport properties of hybrid perovskites possess severe limitations as far as long-timescale instabilities and degradation issues are faced. Several effects are attributed to the presence of mobile ions such as shielding of the internal electrical field upon biasing and chemical interaction between intrinsic moving defects and electrode materials. Ion-originated modulations of electronic properties constitute an essential peace of knowledge to further progress into the halide perovskite device physics and operating modes. Here, ionic current and electronic impedance of lead methylammonium iodide perovskite thick pellets are independently monitored, showing self-consistent patterns. Our findings point to a coupling of ionic and electronic properties as a dynamic doping effect caused by moving ions that act as mobile dopants. The electronic doping profile changes within the bulk as a function of the actual ion inner distribution, then producing a specific time dependence in the electronic conductivity that reproduces time patterns of the type , a clear fingerprint of diffusive transport. Values for the iodine-related defect diffusivity in the range of Dion ⌠10â8 cm2 sâ1, which corresponds to ionic mobilities of about ÎŒion ⌠10â6 cm2 Vâ1 sâ1, are encountered. Technological realizations based on thick perovskite layers would benefit from this fundamental information, as far as long-timescale current stabilization is concerned.This work has received funding from the European Unionâs Horizon 2020 research and innovation program under the Photonics Public Private Partnership (www.photonics21.org) with the project PEROXIS under the grant agreement N° 871336. M.G.-B. acknowledges Generalitat Valenciana for a grant (number GRISOLIAP/2018/073)
High-sensitivity high-resolution X-ray imaging with soft-sintered metal halide perovskites
To realize the potential of artificial intelligence in medical imaging, improvements in imaging capabilities are required, as well as advances in computing power and algorithms. Hybrid inorganicâorganic metal halide perovskites, such as methylammonium lead triiodide (MAPbI3), offer strong X-ray absorption, high carrier mobilities (”) and long carrier lifetimes (Ï), and they are promising materials for use in X-ray imaging. However, their incorporation into pixelated sensing arrays remains challenging. Here we show that X-ray flat-panel detector arrays based on microcrystalline MAPbI3 can be created using a two-step manufacturing process. Our approach is based on the mechanical soft sintering of a freestanding absorber layer and the subsequent integration of this layer on a pixelated backplane. Freestanding microcrystalline MAPbI3 wafers exhibit a sensitivity of 9,300â”CâGyairâ1âcmâ2 with a ÎŒÏ product of 4âĂâ10â4âcm2âVâ1, and the resulting X-ray imaging detector, which has 508âpixels per inch, combines a high spatial resolution of 6âline pairs per millimetre with a low detection limit of 0.22ânGyairâper frame
Design, Herstellung und Charakterisierung organischer Photodioden fĂŒr industrielle und medizinische Anwendungen
Main focus of this work is to prove the feasibility to apply organic photodiodes (OPDs) for medical and industrial applications. The realization of a flat panel X-ray digital imager prototype with the integration of OPDs on top of an amorphous silicon thin film transistor backplane with 256x256 pixels represents the highlight of this thesis. Performances comparable with a commercial available flat panel X-Ray detector based on silicon have been achieved. Furthermore, a new pixel architecture based on the active pixel concept is presented. A better signal to noise ratio for the active pixels compared to the passive pixels is demonstrated.
OPDs are realizable by a simple and low temperature spray-coating process in ambient conditions. In comparison to standard techniques, spray-coating, has revealed to be the most versatile and the best in terms of device performances.
The mechanical characterization of flexible OPDs is reported showing that the current voltage characteristic do not show evident changes in the bent state.
A fully characterization of large area OPDs show that active area upscaling is possible without affecting the performance of the devices. Active areas up to 2.65 cmÂČ are reported.Fokus dieser Arbeit ist die Anwendbarkeit von organischen Fotodioden (OPDs) fĂŒr medizinische und industrielle Anwendungen zu beweisen. Die Realisierung eines flachen und digitalen Röntgendetektor-Prototyp mit der Integration von OPDs auf einer amorphen Silizium DĂŒnnfilmtransistoren Backplane mit 256x256 Pixels vertritt den Höhepunkt dieser Thesis. Leistungen vergleichbar mit einem auf Silizium Basis kommerziellerhĂ€ltlichen Flachbild Röntgendetektor konnten erreicht werden. ZusĂ€tzlich, eine neue Pixelarchitektur die auf das aktive Pixel Konzept basiert wird prĂ€sentiert. Ein besseres Signal zu RauschverhĂ€ltnis fĂŒr den aktiven im Vergleich zu den passiven Pixels wird demonstriert.
OPDs sind durch einen einfachen und unter normalen Umgebungsbedingungen SprĂŒhprozess realisierbar. Im Vergleich mit Standardtechniken hat sich die SprĂŒhbeschichtung als die vielfĂ€ltigste und die Beste in Bezug auf Leistungen offenbart.
Die mechanische Charakterisierung von flexiblen OPDs wird berichtet und es wird gezeigt dass die Stromspannungseigenschaft keine offensichtliche Ănderungen im gebogenen zustand vorweisen.
Eine vollstĂ€ndige Charakterisierung von groĂflĂ€chigen OPDs, demonstriert dass das Hochskalieren ohne LeistungseinbuĂen möglich ist. Aktive FlĂ€chen bis zu 2.65 cmÂČ werden berichtet
Interface Trap States in Organic Photodiodes
Organic semiconductors are attractive for optical sensing applications due to the effortless processing on large active area of several , which is difficult to achieve with solid-state devices. However, compared to silicon photodiodes, sensitivity and dynamic behavior remain a major challenge with organic sensors. Here, we show that charge trapping phenomena deteriorate the bandwidth of organic photodiodes (OPDs) to a few Hz at low-light levels. We demonstrate that, despite the large OPD capacitances of similar to 10 nF , a frequency response in the kHz regime can be achieved at light levels as low as 20 nW by appropriate interface engineering, which corresponds to a 1000-fold increase compared to state-of-the-art OPDs. Such device characteristics indicate that large active area OPDs are suitable for industrial sensing and even match medical requirements for single X-ray pulse detection in the millisecond range
Visible light communications: 375 Mbits/s data rate with a 160 kHz bandwidth organic photodetector and artificial neural network equalization [Invited]
This paper presents an experimental demonstration of a visible light communications link with an light emitting diode and a low-bandwidth organic photodetector as transmitter and receiver, respectively, that achieves sub 4ââMbits/s speeds. An artificial neural network (ANN) equalizer is required in order to achieve such high data rates because of the influence of intersymbol interference. The digital modulation formats tested in this paper are nonreturn-to-zero onâoff keying (OOK), and fourth-order pulse position modulation (4-PPM). Without equalization, data rates of 200 and 300ââkbits/s can be achieved for 4-PPM and OOK, respectively. With ANN equalization, data rates of 2.8 and 3.75ââMbits/s can be achieved for the first time for OOK and 4-PPM, respectively
A 1-Mb/s Visible Light Communications Link With Low Bandwidth Organic Components
This letter presents new experimental results on a 1-Mb/s organic visible light communications system. These results are the first demonstration of a fully organic free space optical communications system. Due to low charge transport characteristics, organic devices are typically highly band limited in the hundreds of kilohertz region (up to 135 kHz in this letter). Therefore, an artificial neural network (ANN) equalizer is required to undo the effects of intersymbol interference. Without the ANN, the maximum link performance corresponds to a data rate of 350 kb/s; however, with the ANN, a transmission speed of 1.15 Mb/s could be supported
Le voyage initiatique (activation et devenir des habitudes d'héritiers migrants issus de la grande bourgeoisie turque)
Ce travail a pour enjeu de dĂ©crypter, dans un systĂšme Ă©conomique et scolaire globalisĂ©, les modalitĂ©s de la reconversion des ressources d'une grande bourgeoisie cosmopolite. L'analyse porte sur les mĂ©canismes de transmission et les rites d'initiation spĂ©cifiques d'un collectif de familles partageant des rĂ©fĂ©rents d'anciennetĂ© et une mĂȘme volontĂ© de mobiliser les ressources offertes par le champ international, et ce dans un contexte inĂ©dit : la Turquie. Le voyage initiatique des hĂ©ritiers de la grande bourgeoisie turque est un voyage au sens littĂ©ral. Il s'articule autour d'un cycle migratoire complexe comportant plusieurs dĂ©parts et plusieurs retours. Mais le retour dĂ©finitif Ă©tant projetĂ© en mĂȘme temps que le premier dĂ©part, l'Ă©quation de leur migration prĂ©sente une inconnue de moins que celle du reste des migrants. Cette recherche montre que la dimension internationale des rites de passage en milieu bourgeois est dĂ©sormais l'Ă©lĂ©ment central d'un modĂšle de transmission dĂ©terminant l'accĂšs aux formations d'excellence et aux positions les plus sĂ©lectives, tant dans le champ international que dans le milieu d'origine. L'originalitĂ© de l'approche proposĂ©e rĂ©side dans la mise en Ă©vidence de combinaisons individualisantes et de situations contradictoires, Ă partir de l'Ă©tude dĂ©taillĂ©e des cadres socialisateurs et des choix relationnels des hĂ©ritiers. Les coĂ»ts du voyage initiatique se rĂ©vĂšlent ainsi trĂšs Ă©levĂ©s. Le moment de la prise de rĂŽle est dĂ©terminĂ© par la gestion des pĂ©riodes critiques d'intensification de la rĂ©flexivitĂ©. En particulier, la durĂ©e et l'impact des dĂ©calages ressentis lors du retour dĂ©finitif en Turquie viennent contredire l'idĂ©e selon laquelle les hĂ©ritiers ont achevĂ©, une fois validĂ©es les Ă©preuves successives de la formation, l'essentiel de leur socialisation. L'issue du processus de transmission est dĂšs lors subordonnĂ©e aux logiques de compromis traduisant la renĂ©gociation permanente, par l'hĂ©ritier, de sa position et des rĂŽles qui lui sont assignĂ©s.The premise of this work is to explore how a cosmopolitan bourgeoisie converts its social resources in the context of a globalized education and a globalized economy, undertaking a novel case study: Turkey. It analyses the transmission process and the specific rites of initiation in a group of families ail possessing an extensive social capital accumulated over time and sharing a common agenda to mobilize the resources offered by the international field . The initiatory journey of the heirs of the Turkish bourgeoisie is a journey in the literal sense, as it involves a complex migratory cycle with several departures and returns. However, since the first departure and the final return are planned at the same time, their migration presents one less unknown factor when compared to other migration patterns. This research shows that the international dimension of the rites of initiation is the central element of a model of transmission determining access to prestigious educational institutions and to the most selective working positions, both on the international market and in the country of origin. This approach is original in that it focuses on the contradictory situations through a detailed study of socializ ing contexts and relationship choices. The costs of the initiatory journey appear then to be very high. The unexpected readjustment crisis experienced in the first years after final return to Turkey is in direct contradiction to the established idea that the heirs have completed their socialization when the successive challenges of their formation have been conquered. The success of transmission process depends on the ability to compromise, as there is a continuing renegotiation of the heirs' position and roles they perceive as assigned to them.PARIS3-BU (751052102) / SudocSudocFranceF
Exploiting Equalization Techniques for Improving Data Rates in Organic Optoelectronic Devices for Visible Light Communications
This paper presents the use of equalization techniques in visible light communication (VLC) systems in order to increase the data rate. Here we investigate two VLC links a silicon (Si) light emitting diode (LED) and an organic photodetector (OPD), and an organic LED (OLED) plus an Si photodetector (PD), together with three equalization schemes of an RC high pass equalizer, a fractionally spaced zero-forcing equalizer (ZF) and an artificial neural network (ANN). In addition we utilize a pre-distortion scheme to enhance the performance of the digital equalizers. For both systems the bit rate achieved are 750 kb/s from a raw bandwidth (BW) of 30 kHz and 550 kb/s from a raw BW of 93 kHz
Optical properties of organic semiconductor blends with near-infrared quantum-dot sensitizers for light harvesting applications
We report an optical investigation of conjugated polymer (P3HT)/fullerene (PCBM) semiconductor blends sensitized by near-infrared absorbing quantum dots (PbS QDs). A systematic series of samples that include pristine, binary and ternary blends of the materials are studied using steady-state absorption, photoluminescence (PL) and ultrafast transient absorption. Measurements show an enhancement of the absorption strength in the near-infrared upon QD incorporation. PL quenching of the polymer and the QD exciton emission is observed and predominantly attributed to intermaterial photoinduced charge transfer processes. Pump-probe experiments show photo-excitations to relax via an initial ultrafast decay while longer-lived photoinduced absorption is attributed to charge transfer exciton formation and found to depend on the relative ratio of QDs to P3HT:PCBM content. PL experiments and transient absorption measurements indicate that interfacial charge transfer processes occur more efficiently at the fullerene/polymer and fullerene/nanocrystal interfaces compared to polymer/nanocrystal interfaces. Thus the inclusion of the fullerene seems to facilitate exciton dissociation in such blends. The study discusses important and rather unexplored aspects of exciton recombination and charge transfer processes in ternary blend composites of organic semiconductors and near-infrared quantum dots for applications in solution-processed photodetectors and solar cell