Improving charge mobility in quantum dot (QD) films is important for the performance of photodetectors, solar cells and light-emitting diodes. However, these applications also require preservation of ...well defined QD electronic states and optical transitions. Here, we present HgTe QD films that show high mobility for charges transported through discrete QD states. A hybrid surface passivation process efficiently eliminates surface states, provides tunable air-stable n and p doping and enables hysteresis-free filling of QD states evidenced by strong conductance modulation. QD films dried at room temperature without any post-treatments exhibit mobility up to μ ~ 8 cm
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at a low carrier density of less than one electron per QD, band-like behaviour down to 77 K, and similar drift and Hall mobilities at all temperatures. This unprecedented set of electronic properties raises important questions about the delocalization and hopping mechanisms for transport in QD solids, and introduces opportunities for improving QD technologies.
The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on ...densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p- and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction.
A novel electrode material for sodium-ion batteries (NIBs), Na3V2(PO4)3 with a rhombohedral, Na+ superionic conductor (NASICON)-type structure, was synthesised via a solid-state carbon-thermal ...reduction reaction assisted by mechanochemical activation. Electron microscopy analysis showed that the synthesised Na3V2(PO4)3 particles had an average size of 300 nm, being coated with a uniform layer of carbon 3 nm in thickness. As a cathode material, Na3V2(PO4)3/C exhibited an initial specific discharge capacity of 98.17 mAh g−1 at 0.1C for potentials ranging from 2.5 to 3.8 V. This was owing to the V3+/V4+ redox couple, which corresponded to the two-phase transition between Na3V2(PO4)3 and NaV2(PO4)3. The cathode lost 4.92% of its discharge specific capacity after 50 cycles. As an anode material, Na3V2(PO4)3/C exhibited an initial specific discharge capacity of 63.2 mAh g−1 at 0.1C for potentials ranging from 1.0 to 2.5 V. This was owing to the V2+/V3+ redox couple, which corresponded to the two-phase transition between Na3V2(PO4)3 and Na4V2(PO4)3. The anode lost approximately 5.41% of its discharge specific capacity after 50 cycles. The three-dimensional channel structure of NaV2(PO4)3 and the changes induced in its lattice parameters during the charge/discharge processes were simulated on the basis of density functional theory.
•Na3V2(PO4)3/C was synthesised through glucose-assisted carbon-thermal reduction.•Na3V2(PO4)3/C has 3.4 V voltage plateau against Na with ca. 98 mAh g−1.•The product exhibited excellent cycling stability and rate performance.•The Na3V2(PO4)3/C can be used as both a cathodic and an anodic material.•The structure changes of Na3V2(PO4)3 during electrode reactions were simulated.
Planar perovskite solar cells (PSCs) made entirely via solution processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and ...perovskite-based tandem devices. However, these PSCs require an electron-selective layer that performs well with similar processing. We report a contact-passivation strategy using chlorine-capped TiO₂ colloidal nanocrystal film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after dark recovery) of their initial performance after 500 hours of continuous room-temperature operation at their maximum power point under 1-sun illumination (where 1 sun is defined as the standard illumination at AM1.5, or 1 kilowatt/square meter).
Radioluminescent materials (scintillators) are widely applied in medical imaging, nondestructive testing, security inspection, nuclear and radiation industries, and scientific research. Recently, ...all‐inorganic lead halide perovskite nanocrystal (NC) scintillators have attracted great attention due to their facile solution processability and ultrasensitive X‐ray detection, which allows for large area and flexible X‐ray imaging. However, the light yield of these perovskite NCs is relatively low because of the strong self‐absorption that reduces the light out‐coupling efficiency. Here, NCs with self‐trapped excitons emission are demonstrated to be sensitive, reabsorption‐free scintillators. Highly luminescent and stable Cs3Cu2I5 NCs with a photoluminescence quantum yields of 73.7%, which is a new record for blue emission lead‐free perovskite or perovskite‐like NCs, is produced with the assistance of InI3. The PL peak of the Cs3Cu2I5 NCs locates at 445 nm that matches with the response peak of a silicon photomultiplier. Thus, Cs3Cu2I5 NCs are demonstrated as efficient scintillators with zero self‐absorption and extremely high light yield (≈79 279 photons per MeV). Both Cs3Cu2I5 NC colloidal solution and film exhibit strong radioluminescence under X‐ray irradiation. The potential application of Cs3Cu2I5 NCs as reabsorption‐free, low cost, large area, and flexible scintillators is demonstrated by a prototype X‐ray imaging with a high spatial resolution.
Nanocrystals (NCs) with self‐trapped excitons emission are demonstrated to be sensitive, reabsorption‐free scintillators. Highly blue‐emissive and stable Cs3Cu2I5 NCs with a photoluminescence quantum yield of 73.7% are produced. These Cs3Cu2I5 NCs show a strong and reabsorption‐free radioluminescence under X‐ray irradiation with an extremely high light yield, which makes them promising scintillators for low cost, large area, and flexible X‐ray imaging.
Solution-processed planar perovskite devices are highly desirable in a wide variety of optoelectronic applications; however, they are prone to hysteresis and current instabilities. Here we report the ...first perovskite-PCBM hybrid solid with significantly reduced hysteresis and recombination loss achieved in a single step. This new material displays an efficient electrically coupled microstructure: PCBM is homogeneously distributed throughout the film at perovskite grain boundaries. The PCBM passivates the key PbI3(-) antisite defects during the perovskite self-assembly, as revealed by theory and experiment. Photoluminescence transient spectroscopy proves that the PCBM phase promotes electron extraction. We showcase this mixed material in planar solar cells that feature low hysteresis and enhanced photovoltage. Using conductive AFM studies, we reveal the memristive properties of perovskite films. We close by positing that PCBM, by tying up both halide-rich antisites and unincorporated halides, reduces electric field-induced anion migration that may give rise to hysteresis and unstable diode behaviour.
Colloidal quantum dot (CQD) solar cells are solution-processed photovoltaics with broad spectral absorption tunability. Major advances in their efficiency have been made via improved CQD surface ...passivation and device architectures with enhanced charge carrier collection. Herein, we demonstrate a new strategy to improve further the passivation of CQDs starting from the solution phase. A cosolvent system is employed to tune the solvent polarity in order to achieve the solvation of methylammonium iodide (MAI) and the dispersion of hydrophobic PbS CQDs simultaneously in a homogeneous phase, otherwise not achieved in a single solvent. This process enables MAI to access the CQDs to confer improved passivation. This, in turn, allows for efficient charge extraction from a thicker photoactive layer device, leading to a certified solar cell power conversion efficiency of 10.6%, a new certified record in CQD photovoltaics.
Bandtail states in disordered semiconductor materials result in losses in open-circuit voltage (V
) and inhibit carrier transport in photovoltaics. For colloidal quantum dot (CQD) films that promise ...low-cost, large-area, air-stable photovoltaics, bandtails are determined by CQD synthetic polydispersity and inhomogeneous aggregation during the ligand-exchange process. Here we introduce a new method for the synthesis of solution-phase ligand-exchanged CQD inks that enable a flat energy landscape and an advantageously high packing density. In the solid state, these materials exhibit a sharper bandtail and reduced energy funnelling compared with the previous best CQD thin films for photovoltaics. Consequently, we demonstrate solar cells with higher V
and more efficient charge injection into the electron acceptor, allowing the use of a closer-to-optimum bandgap to absorb more light. These enable the fabrication of CQD solar cells made via a solution-phase ligand exchange, with a certified power conversion efficiency of 11.28%. The devices are stable when stored in air, unencapsulated, for over 1,000 h.
Graphdiyne, a novel large π‐conjugated carbon hole transporting material, is employed as anode buffer layer in colloidal quantum dots solar cells. Power conversion efficiency is notably enhanced to ...10.64% from 9.49% compared to relevant reference devices. Hole transfer from the quantum dot solid active layer to the anode can be appreciably enhanced only by using graphdiyne to lower the work function of the colloidal quantum dot solid. It is found that the all‐carbon buffer layer prolongs the carrier lifetime, reducing surface recombination on the previously neglected back side of the photovoltaic device. Remarkably, the device also shows high long‐term stability in ambient air. The results demonstrate that graphdiyne may have diverse applications in enhancing optoelectronic devices.
The novel large π‐conjugated carbon hole transporting material, graphdiyne (GD) is used as anode buffer layer in PbS CQD solar cells. GD increases carrier lifetime and reduces carrier recombination inside the PbS CQD solar cells. Notably, a high power conversion efficiency of 10.64% is achieved, and the device also shows high long‐term stability in ambient air.
A crosslinked hole‐extracting electrical contact is reported, which simultaneously improves the stability and lowers the hysteresis of perovskite solar cells. Polymerizable monomers and crosslinking ...processes are developed to obviate in situ degradation of the under lying perovskite. The crosslinked material is band‐aligned with perovskite. The required free carrier density is induced by a high‐work‐function metal oxide layer atop the device, following a remote‐doping strategy.
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