Schizophrenia (SZ) is a widespread psychiatric disorder that is traditionally characterized by positive and negative symptoms. However, recent focus has shifted to cognitive deficits as a crucial aspect. The cerebellum, conventionally tied to motor coordination, is now recognized as pivotal in the pathophysiology of SZ cognitive impairments. Proposed disruptions in the cortico-cerebellar-thalamic-cortico circuit contribute to these deficits. Despite evidence of cerebellar abnormalities, within-cerebellum functional connectivity is often overlooked. This study explores spontaneous functional interactions within the cerebellum and their link to cognitive deficits in SZ. Using a multi-domain task battery (MDTB) parcellation, fMRI data from SZ patients and healthy controls were analyzed. Significant differences in cerebellar connectivity emerged, particularly in regions related to attention, language, and memory processing. Correlations between connectivity values and SZ symptomatology were identified. A post hoc analysis, considering the patients' hallucination vulnerability, revealed distinct connectivity patterns. Non-hallucinating and low-hallucinating SZ patients exhibited higher cerebellar connectivity than high-hallucinating patients, especially in language and motor control regions. These findings suggest a gradient of cerebellar connectivity alterations corresponding to hallucination vulnerability in SZ patients. This study offers novel insights into cerebellar impairments in SZ, highlighting the role of within-cerebellum connectivity in cognitive deficits. The observed connectivity patterns in language-related regions contribute to understanding language development and auditory verbal hallucinations in SZ.
III-V colloidal quantum dots (CQDs) are of interest in infrared photodetection, and recent developments in CQDs synthesis and surface engineering have improved performance. Here this work investigates photodetector stability, finding that the diffusion of zinc ions from charge transport layers (CTLs) into the CQDs active layer increases trap density therein, leading to rapid and irreversible performance loss during operation. In an effort to prevent this, this work introduces organic blocking layers between the CQDs and ZnO layers; but these negatively impact device performance. The device is then, allowing to use a C60:BCP as top electron-transport layer (ETL) for good morphology and process compatibility, and selecting NiOX as the bottom hole-transport layer (HTL). The first round of NiOX -based devices show efficient light response but suffer from high leakage current and a low open-circuit voltage (Voc) due to pinholes. This work introduces poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) with NiOX NC to form a hybrid HTL, an addition that reduces pinhole formation, interfacial trap density, and bimolecular recombination, enhancing carrier harvesting. The photodetectors achieve 53% external quantum efficiency (EQE) at 970 nm at 1 V applied bias, and they maintain 95% of initial performance after 19 h of continuous illuminated operation. The photodetectors retain over 80% of performance after 80 days of shelf storage.
III-V colloidal quantum dots (CQDs) are promising materials for optoelectronic applications, for they avoid heavy metals while achieving absorption spanning the visible to the infrared (IR). However, the covalent nature of III-V CQDs requires the development of new passivation strategies to fabricate conductive CQD solids for optoelectronics: this work shows herein that ligand exchanges, previously developed in II-VI and IV-VI quantum dots and employing a single ligand, do not fully passivate CQDs, and that this curtails device efficiency. Guided by density functional theory (DFT) simulations, this work develops a co-passivation strategy to fabricate indium arsenide CQD photodetectors, an approach that employs the combination of X-type methyl ammonium acetate (MaAc) and Z-type ligands InBr3 . This approach maintains charge carrier mobility and improves passivation, seen in a 25% decrease in Stokes shift, a fourfold reduction in the rate of first-exciton absorption linewidth broadening over time-under-stress, and leads to a doubling in photoluminescence (PL) lifetime. The resulting devices show 37% external quantum efficiency (EQE) at 950 nm, the highest value reported for InAs CQD photodetectors.
Quantum Dots , Ligands , Electric Conductivity
Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm2 V-1 s-1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 ns-the fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940 nm.
Colloidal quantum dots (CQD) have emerged as attractive materials for infrared (IR) photodetector (PD) applications because of their tunable bandgaps and facile processing. Presently, zinc oxide is the electron-transport layer (ETL) of choice in CQD PDs; however, ZnO relies on continuous ultraviolet (UV) illumination to remove adsorbed oxygen and maintain high external quantum efficiency (EQE), speed, and photocurrent. Here, it is shown that ZnO is dominated by electropositive crystal planes which favor excessive oxygen adsorption, and that this leads to a high density of trap states, an undesired shift in band alignment, and consequent poor performance. Over prolonged operation without UV exposure, oxygen accumulates at the electropositive planes, trapping holes and degrading performance. This problem is addressed by developing an electroneutral plane composition at the ZnO surface, aided by atomic layer deposition (ALD) as the means of materials processing. It is found that ALD ZnO has 10× lower binding energy for oxygen than does conventionally deposited ZnO. IR CQD PDs made with this ETL do not require UV activation to maintain low dark current and high EQE.
III-V colloidal quantum dots (CQDs) are promising semiconducting materials for optoelectronic applications; however, their strong covalent character requires a distinct approach to surface management compared with widely investigated II-VI and IV-VI CQDs-dots, which by contrast are characterized by an ionic nature. Here we show stoichiometric reconstruction in InAs CQDs by ligand exchange. In particular, we find that indium-carboxylate ligands, which passivate as-synthesized InAs CQDs and are responsible for In-rich surfaces, can be replaced by anionic ligands such as thiols. This enables the production of inks consisting of balanced-stoichiomety CQDs; this is distinct from what is observed in II-VI and IV-VI CQDs, in which thiols replace carboxylates. The approach enables the implementation of InAs CQD solids as the active layer in photodiode detectors that exhibit an external quantum efficiency of 36% at 930 nm and a photoresponse time of 65 ns, which is 4 times shorter than that of reference PbS CQD devices.
Charge carrier transport in colloidal quantum dot (CQD) solids is strongly influenced by coupling among CQDs. The shape of as-synthesized CQDs results in random orientational relationships among facets in CQD solids, and this limits the CQD coupling strength and the resultant performance of optoelectronic devices. Here, colloidal-phase reconstruction of CQD surfaces, which improves facet alignment in CQD solids, is reported. This strategy enables control over CQD faceting and allows demonstration of enhanced coupling in CQD solids. The approach utilizes post-synthetic resurfacing and unites surface passivation and colloidal stability with a propensity for dots to couple via (100):(100) facets, enabling increased hole mobility. Experimentally, the CQD solids exhibit a 10× increase in measured hole mobility compared to control CQD solids, and enable photodiodes (PDs) exhibiting 70% external quantum efficiency (vs 45% for control devices) and specific detectivity, D* > 1012 Jones, each at 1550 nm. The photodetectors feature a 7 ns response time for a 0.01 mm2 area-the fastest reported for solution-processed short-wavelength infrared PDs.
The need for optoelectronic and chemical compatibility between the layers in colloidal quantum dot (CQD) photovoltaic devices remains a bottleneck in further increasing performance. Conjugated polymers are promising candidates as new hole-transport layer (HTL) materials in CQD solar cells (CQD-SCs) owing to the highly tunable optoelectronic properties and compatible chemistries. A diketopyrrolopyrrole-based polymer with benzothiadiazole derivatives (PD2FCT-29DPP) as an HTL in these devices is reported. The energy level, molecular orientation, and hole mobility of this HTL are manipulated through molecular engineering. By levering the polymer's optical absorption spectrum complementary to that of the CQD active layer, EQE across the visible and near-infrared regions is maximized. As a result, a PD2FCT-29DPP-based device exhibits a fill factor of 70% and approximately 35% efficiency enhancement compared to a PTB7-based device.
Monolithically integrated hybrid tandem solar cells (TSCs) that combine solution-processed colloidal quantum dot (CQD) and organic molecules are a promising device architecture, able to complement the absorption across the visible to the infrared. However, the performance of organic/CQD hybrid TSCs has not yet surpassed that of single-junction CQD solar cells. Here, a strategic optical structure is devised to overcome the prior performance limit of hybrid TSCs by employing a multibuffer layer and a dual near-infrared (NIR) absorber. In particular, a multibuffer layer is introduced to solve the problem of the CQD solvent penetrating the underlying organic layer. In addition, the matching current of monolithic TSCs is significantly improved to 15.2 mA cm-2 by using a dual NIR organic absorber that complements the absorption of CQD. The hybrid TSCs reach a power conversion efficiency (PCE) of 13.7%, higher than that of the corresponding individual single-junction cells, representing the highest efficiency reported to date for CQD-based hybrid TSCs.
Surface ligands enable control over the dispersibility of colloidal quantum dots (CQDs) via steric and electrostatic stabilization. Today's device-grade CQD inks have consistently relied on highly polar solvents: this enables facile single-step deposition of multi-hundred-nanometer-thick CQD films; but it prevents the realization of CQD film stacks made up of CQDs having different compositions, since polar solvents redisperse underlying films. Here we introduce aromatic ligands to achieve process-orthogonal CQD inks, and enable thereby multifunctional multilayer CQD solids. We explore the effect of the anchoring group of the aromatic ligand on the solubility of CQD inks in weakly-polar solvents, and find that a judicious selection of the anchoring group induces a dipole that provides additional CQD-solvent interactions. This enables colloidal stability without relying on bulky insulating ligands. We showcase the benefit of this ink as the hole transport layer in CQD optoelectronics, achieving an external quantum efficiency of 84% at 1210 nm.
Colloidal quantum dots (CQDs) are of interest for optoelectronic applications owing to their tunable properties and ease of processing. Large-diameter CQDs offer optical response in the infrared (IR), beyond the bandgap of c-Si and perovskites. The absorption coefficient of IR CQDs (≈104 cm-1) entails the need for micrometer-thick films to maximize the absorption of IR light. This exceeds the thickness compatible with the efficient extraction of photogenerated carriers, a fact that limits device performance. Here, CQD bulk heterojunction solids are demonstrated that, with extended carrier transport length, enable efficient IR light harvesting. An in-solution doping strategy for large-diameter CQDs is devised that addresses the complex interplay between (100) facets and doping agents, enabling to control CQD doping, energetic configuration, and size homogeneity. The hetero-offset between n-type CQDs and p-type CQDs is manipulated to drive the transfer of electrons and holes into distinct carrier extraction pathways. This enables to form active layers exceeding thicknesses of 700 nm without compromising open-circuit voltage and fill factor. As a result, >90% charge extraction efficiency across the ultraviolet to IR range (350-1400 nm) is documented.
Increasing the power conversion efficiency (PCE) of colloidal quantum dot (CQD) solar cells has relied on improving the passivation of CQD surfaces, enhancing CQD coupling and charge transport, and advancing device architecture. The presence of hydroxyl groups on the nanoparticle surface, as well as dimers-fusion between CQDs-has been found to be the major source of trap states, detrimental to optoelectronic properties and device performance. Here, we introduce a CQD reconstruction step that decreases surface hydroxyl groups and dimers simultaneously. We explored the dynamic interaction of charge carriers between band-edge states and trap states in CQDs using time-resolved spectroscopy, showing that trap to ground-state recombination occurs mainly from surface defects in coupled CQD solids passivated using simple metal halides. Using CQD reconstruction, we demonstrate a 60% reduction in trap density and a 25% improvement in charge diffusion length. These translate into a PCE of 12.5% compared to 10.9% for control CQDs.
Colloidal quantum dots (CQDs) are of interest in light of their solution-processing and bandgap tuning. Advances in the performance of CQD optoelectronic devices require fine control over the properties of each layer in the device materials stack. This is particularly challenging in the present best CQD solar cells, since these employ a p-type hole-transport layer (HTL) implemented using 1,2-ethanedithiol (EDT) ligand exchange on top of the CQD active layer. It is established that the high reactivity of EDT causes a severe chemical modification to the active layer that deteriorates charge extraction. By combining elemental mapping with the spatial charge collection efficiency in CQD solar cells, the key materials interface dominating the subpar performance of prior CQD PV devices is demonstrated. This motivates to develop a chemically orthogonal HTL that consists of malonic-acid-crosslinked CQDs. The new crosslinking strategy preserves the surface chemistry of the active layer beneath, and at the same time provides the needed efficient charge extraction. The new HTL enables a 1.4× increase in charge carrier diffusion length in the active layer; and as a result leads to an improvement in power conversion efficiency to 13.0% compared to EDT standard cells (12.2%).
Control over carrier type and doping levels in semiconductor materials is key for optoelectronic applications. In colloidal quantum dots (CQDs), these properties can be tuned by surface chemistry modification, but this has so far been accomplished at the expense of reduced surface passivation and compromised colloidal solubility; this has precluded the realization of advanced architectures such as CQD bulk homojunction solids. Here we introduce a cascade surface modification scheme that overcomes these limitations. This strategy provides control over doping and solubility and enables n-type and p-type CQD inks that are fully miscible in the same solvent with complete surface passivation. This enables the realization of homogeneous CQD bulk homojunction films that exhibit a 1.5 times increase in carrier diffusion length compared with the previous best CQD films. As a result, we demonstrate the highest power conversion efficiency (13.3%) reported among CQD solar cells.
Infrared-absorbing colloidal quantum dots (IR CQDs) are materials of interest in tandem solar cells to augment perovskite and cSi photovoltaics (PV). Today's best IR CQD solar cells rely on the use of passivation strategies based on lead iodide; however, these fail to passivate the entire surface of IR CQDs. Lead chloride passivated CQDs show improved passivation, but worse charge transport. Lead bromide passivated CQDs have higher charge mobilities, but worse passivation. Here a mixed lead-halide (MPbX) ligand exchange is introduced that enables thorough surface passivation without compromising transport. MPbX-PbS CQDs exhibit properties that exceed the best features of single lead-halide PbS CQDs: they show improved passivation (43 ± 5 meV vs 44 ± 4 meV in Stokes shift) together with higher charge transport (4 × 10-2 ± 3 × 10-3 cm2 V-1 s-1 vs 3 × 10-2 ± 3 × 10-3 cm2 V-1 s-1 in mobility). This translates into PV devices having a record IR open-circuit voltage (IR Voc ) of 0.46 ± 0.01 V while simultaneously having an external quantum efficiency of 81 ± 1%. They provide a 1.7× improvement in the power conversion efficiency of IR photons (>1.1 µm) relative to the single lead-halide controls reported herein.
Colloidal quantum dots (CQDs) can be used to extend the response of solar cells, enabling the utilization of solar power that lies to the red of the bandgap of c-Si and perovskites. To achieve largely complete absorption of infrared (IR) photons in CQD solids requires thicknesses on the micrometer range; however, this exceeds the typical diffusion lengths (≈300 nm) of photoexcited charges in these materials. Nanostructured metal back electrodes that grant the cell efficient IR light trapping in thin active layers with no deterioration of the electrical properties are demonstrated. Specifically, a new hole-transport layer (HTL) is developed and directly nanostructured. Firstly, a material set to replace conventional rigid HTLs in CQD devices is developed with a moldable HTL that combines the mechanical and chemical requisites for nanoimprint lithography with the optoelectronic properties necessary to retain efficient charge extraction through an optically thick layer. The new HTL is nanostructured in a 2D lattice and conformally coated with MoO3 /Ag. The photonic structure in the back electrode provides a record photoelectric conversion efficiency of 86%, beyond the Si bandgap, and a 22% higher IR power conversion efficiency compared to the best previous reports.
The dynamics of photoluminescence (PL) from nanocrystal quantum dots (QDs) is significantly affected by the reversible trapping of photoexcited charge carriers. This process occurs after up to 50% of the absorption events, depending on the type of QD considered, and can extend the time between the photoexcitation and relaxation of the QD by orders of magnitude. Although many optoelectronic applications require QDs assembled into a QD solid, until now, reversible trapping has been studied only in (ensembles of) spatially separated QDs. Here, we study the influence of reversible trapping on the excited-state dynamics of CdSe/CdS core/shell QDs when they are assembled into close-packed "supraparticles". Time- and spectrally resolved photoluminescence (PL) measurements reveal competition among spontaneous emission, reversible charge-carrier trapping, and Förster resonance energy transfer between the QDs. While Förster transfer causes the PL to red-shift over the first 20-50 ns after excitation, reversible trapping stops and even reverses this trend at later times. We can model this behavior with a simple kinetic Monte Carlo simulation by considering that charge-carrier trapping leaves the QDs in a state with zero oscillator strength in which no energy transfer can occur. Our results highlight that reversible trapping significantly affects the energy and charge-carrier dynamics for applications in which QDs are assembled into a QD solid.
