32 research outputs found
Foto-Hallovská spektroskopie a laserem indukované tranzientní proudy v polovodičových detektorech na bázi CdTe
Název: Foto-Hallovská spektroskopie a laserem indukované tranzientní proudy v polovodičových detektorech na bázi CdTe Autor: Artem Musiienko Pracoviště: Fyzikální Ústav, MFF UK Vedoucí disertační práce: Prof. RNDr. Roman Grill, CSc, Fyzikální Ústav, MFF UK Abstrakt: Tellurid kademnatý, tellurid zinečnato-kademnatý a tellurid manganato-kademnatý jsou důležité polovodiče používané v detektorech záření, solárních článcích a elektrooptických modulátorech. Jejich elektrické a optické vlastnosti jsou podstatně ovlivňovány poruchami, které se projevují jako energetické hladiny uvnitř pásu zakázaných energií. Tyto poruchy tvoří rekombinační a pasťová centra, která zachytávají světlem generované nosiče a zhoršují detekční vlastnosti detektorů. Současně změna obsazení hladin vede k nabíjení objemu detektoru, což vede ke stínění přiloženého elektrického pole a ke ztrátě citlivosti detektoru. Podrobná znalost struktury defektů v krystalu je proto nezbytná pro stanovení kvality detektoru a také pro možnost snížení koncentrace defektů. Tato dizertace se zabývá výzkumem hlubokých energetických hladin v detektorových materiálech na bázi CdTe s vysokým měrným elektrickým odporem pomocí foto-Hallovy spektroskopie. Klasický přístup je také rozšířen o paralelní excitaci světlem o dvou vlnových délkách a monochromatickou...Title: Photo-Hall effect spectroscopy and laser-induced transient currents in CdTe-based semiconductor radiation detectors Author: Artem Musiienko Department / Institute: Institute of Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Prof. RNDr. Roman Grill, CSc, Institute of Physics, Faculty of Mathematics and Physics, Charles University Abstract: Cadmium Telluride, Cadmium Zinc Telluride, and Cadmium Manganese Telluride are important semiconductors with applications in radiation detection, solar cells, and electro-optic modulators. Their electrical and optical properties are principally controlled by defects forming energy levels within the bandgap. Such defects create recombination and trapping centers capturing photo- created carriers and depreciating the performance of the detector. Simultaneously, the changed occupancy of levels leads to the charging of detector's bulk, which results in the screening of applied bias and the loss of detector's sensitivity. Detailed knowledge of crystal defect structure is thus necessary for the predictable detector work and also for the possibility to reduce the structural defects concentration. This thesis reports on the investigation of deep energy levels in CdTe-based high resistivity and detector-grade materials by...Fyzikální ústav UKInstitute of Physics of Charles UniversityMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
Foto-Hallovská spektroskopie a laserem indukované tranzientní proudy v polovodičových detektorech na bázi CdTe
Název: Foto-Hallovská spektroskopie a laserem indukované tranzientní proudy v polovodičových detektorech na bázi CdTe Autor: Artem Musiienko Pracoviště: Fyzikální Ústav, MFF UK Vedoucí disertační práce: Prof. RNDr. Roman Grill, CSc, Fyzikální Ústav, MFF UK Abstrakt: Tellurid kademnatý, tellurid zinečnato-kademnatý a tellurid manganato-kademnatý jsou důležité polovodiče používané v detektorech záření, solárních článcích a elektrooptických modulátorech. Jejich elektrické a optické vlastnosti jsou podstatně ovlivňovány poruchami, které se projevují jako energetické hladiny uvnitř pásu zakázaných energií. Tyto poruchy tvoří rekombinační a pasťová centra, která zachytávají světlem generované nosiče a zhoršují detekční vlastnosti detektorů. Současně změna obsazení hladin vede k nabíjení objemu detektoru, což vede ke stínění přiloženého elektrického pole a ke ztrátě citlivosti detektoru. Podrobná znalost struktury defektů v krystalu je proto nezbytná pro stanovení kvality detektoru a také pro možnost snížení koncentrace defektů. Tato dizertace se zabývá výzkumem hlubokých energetických hladin v detektorových materiálech na bázi CdTe s vysokým měrným elektrickým odporem pomocí foto-Hallovy spektroskopie. Klasický přístup je také rozšířen o paralelní excitaci světlem o dvou vlnových délkách a monochromatickou...Title: Photo-Hall effect spectroscopy and laser-induced transient currents in CdTe-based semiconductor radiation detectors Author: Artem Musiienko Department / Institute: Institute of Physics, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Prof. RNDr. Roman Grill, CSc, Institute of Physics, Faculty of Mathematics and Physics, Charles University Abstract: Cadmium Telluride, Cadmium Zinc Telluride, and Cadmium Manganese Telluride are important semiconductors with applications in radiation detection, solar cells, and electro-optic modulators. Their electrical and optical properties are principally controlled by defects forming energy levels within the bandgap. Such defects create recombination and trapping centers capturing photo- created carriers and depreciating the performance of the detector. Simultaneously, the changed occupancy of levels leads to the charging of detector's bulk, which results in the screening of applied bias and the loss of detector's sensitivity. Detailed knowledge of crystal defect structure is thus necessary for the predictable detector work and also for the possibility to reduce the structural defects concentration. This thesis reports on the investigation of deep energy levels in CdTe-based high resistivity and detector-grade materials by...Fyzikální ústav UKInstitute of Physics of Charles UniversityFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Anticorrelated Photoluminescence and Free Charge Generation Proves Field-Assisted Exciton Dissociation in Low-Offset PM6:Y5 Organic Solar Cells
Understanding the origin of inefficient photocurrent generation in organic
solar cells with low energy offset remains key to realizing high performance
donor-acceptor systems. Here, we probe the origin of field-dependent free
charge generation and photoluminescence in non-fullerene acceptor (NFA) based
organic solar cells using the polymer PM6 and NFA Y5 - a non-halogenated
sibling to Y6, with a smaller energetic offset to PM6. By performing
time-delayed collection field (TDCF) measurements on a variety of samples with
different electron transport layers and active layer thickness, we show that
the fill factor and photocurrent are limited by field-dependent free charge
generation in the bulk of the blend. We also introduce a new method of TDCF
called m-TDCF to prove the absence of artefacts from non-geminate recombination
of photogenerated- and dark charge carriers near the electrodes. We then
correlate free charge generation with steady state photoluminescence intensity,
and find perfect anticorrelation between these two properties. Through this, we
conclude that photocurrent generation in this low offset system is entirely
controlled by the field dependent exciton dissociation into charge transfer
states
Self-Doping of the Transport Layers Decreases the Bimolecular Recombination by Reducing Static Disorder
Electron-transport layers (ETLs) have a crucial role in the solar cells’ performance. Generally, ETLs are characterized in terms of the interface properties and conductivity rather than their effect on the photoactive layer. Herein, two ETLs, 2,9-bis(3-((3-(dimethylamino)propyl)amino)propyl)anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10(2H,9H)-tetraone (PDINN) and 2,9-bis[3-(dimethyloxidoamino)propyl]anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10(2H,9H)-tetrone, are compared in the conventional PM6:Y6 organic solar cell (OSC) structure and the influence of the ETL on the photoactive layer is shown. It is shown that a significant portion of the unpaired electrons of PDINN is mobile by combining electron paramagnetic resonance and Hall effect measurements. It is established that the high doping in PDINN ETL changes the dark electron concentration of the photoactive layer. The impacts of this change in the photoactive layer can be observed in the reduced static energetic disorder, and subsequently in the (nonradiative) recombination of free carriers. The results can be used to suppress nonradiative recombination in OSC, which can significantly boost their efficiency
Internal electric fields control triplet formation in halide perovskite-sensitized photon upconverters
Halide perovskite-based photon upconverters utilize perovskite thin films to sensitize triplet exciton formation in a small-molecule layer, driving triplet-triplet annihilation upconversion. Despite having excellent carrier mobility, these systems suffer from inefficient triplet formation at the perovskite/annihilator interface. We studied triplet formation in formamidinium-methylammonium lead iodide/rubrene bilayers using photoluminescence and surface photovoltage methods. By studying systems constructed on glass as well as hole-selective substrates, comprising self-assembled layers of the carbazole derivative 2PACz ([2-(9H-carbazol-9-yl)ethyl]phosphonic acid) on indium-doped tin oxide, we saw how changes in the carrier dynamics induced by the hole-selective substrate perturbed triplet formation at the perovskite/rubrene interface. We propose that an internal electric field, caused by hole transfer at the perovskite/rubrene interface, strongly affects triplet exciton formation, accelerating exciton-forming electron-hole encounters at the interface but also limiting the hole density in rubrene at high excitation densities. Controlling this field is a promising path to improving triplet formation in perovskite/annihilator upconverters
Whats special about Y6; the working mechanism of neat Y6 organic solar cell
Non-fullerene acceptors (NFA) have delivered advance in bulk heterojunction
organic solar cell efficiencies, with the significant milestone of 20% now in
sight. However, these materials challenge the accepted wisdom of how organic
solar cells work. In this work we present neat Y6 device with efficiency above
4.5%. We thoroughly investigate mechanisms of charge generation and
recombination as well as transport in order to understand what is special about
Y6. Our data suggest Y6 generates bulk free charges, with ambipolar mobility,
which can be extracted in the presence of transport layersComment: 11 pages, 5 figure
Defects in Hybrid Perovskites: The Secret of Efficient Charge Transport
The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI(3), giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes
Interface Modification for Energy Levels Alignment and Charge Extraction in CsPbI Perovskite Solar Cells
In perovskite solar cells (PSCs) energy levels alignment and charge
extraction at the interfaces are the essential factors directly affecting the
device performance. In this work, we present a modified interface between
all-inorganic CsPbI perovskite and its hole selective contact
(Spiro-OMeTAD), realized by a dipole molecule trioctylphosphine oxide (TOPO),
to align the energy levels. On a passivated perovskite film, by n-Octyl
ammonium Iodide (OAI), we created an upward surface band-bending at the
interface by TOPO treatment. This improved interface by the dipole molecule
induces a better energy level alignment and enhances the charge extraction of
holes from the perovskite layer to the hole transport material. Consequently, a
Voc of 1.2 V and high-power conversion efficiency (PCE) of over 19% were
achieved for inorganic CsPbI perovskite solar cells. Further, to
demonstrate the effect of the TOPO dipole molecule, we present a layer-by-layer
charge extraction study by transient surface photovoltage technique (trSPV)
accomplished by charge transport simulation.Comment: 20 pages, 4 Figure