Multiple Exciton Generation and Dynamics in InP/CdS Colloidal Quantum Dots

Smith, Carole; Leontiadou, Marina A.; Clark, Pip C. J.; Lydon, Claire; Savjani, Nicky; Spencer, Ben F.; Flavell, Wendy R.; O’Brien, Paul; Binks, David J.

doi:10.1021/acs.jpcc.6b11744

Cited by 25 publications

(20 citation statements)

References 47 publications

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“…The In 3d 5/2 peak at 445.0 eV ± 0.1 eV and N 1s at 398.8 eV ± 0.1 eV binding energies, as determined by SR‐XPS were consistent with those of characteristic InN and similar structures. [ 24 ] Further species were observed for the N 1s and In 3d 5/2 core levels at the lowest sampling depth (225 eV, Figures S11 and S12, respectively, Supporting Information). The N 1s peak at 400.4 eV ± 0.1 eV could be attributed to protonated N species, such as amines and ammonia, and the higher binding energy the In 3d peaks was consistent with In hydroxide or In oxynitride.…”

Section: Resultsmentioning

confidence: 99%

“…While we currently assign this structure as a doped‐nitride and suggest the emission is band edge in origin, it is well known that defects and dopants play a large role in the emission of nitrides and III‐V materials in general. [ 24b,30 ] It must be noted that the complexities of the material and reaction could mask the effects of defects and potential dopants, with the potential for producing unexpected related structures such as the half‐Heusler compounds mentioned earlier.…”

Section: Resultsmentioning

confidence: 99%

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Photo‐ and Electroluminescence from Zn‐Doped InN Semiconductor Nanocrystals

Fairclough

Taylor

Smith

et al. 2020

Advanced Optical Materials

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There is a critical research need for efficient luminescent colloidal nanocrystals, free from cadmium and lead whose toxicity subjects them to usage restrictions, with applications from display devices to biology. Approaches to directly replace cadmium‐based materials have mainly focused on indium phosphide‐based nanocrystals, however these too are subject to concerns over toxicity. Few other alternatives have been found that can compete with the emission range and efficiency of Cd‐ and Pb‐based nanocrystals. Group III‐nitride nanocrystals, and their alloys, offer the exciting potential to tune bandgap energies from the ultraviolet to the near infrared yet a robust route toward efficient luminescent nitride nanocrystals is lacking. Here, the synthesis of photoluminescent indium zinc nitride quantum dots exhibiting tunable emission through the visible to near infrared spectra region, with quantum yields of up to 30% is reported. Capping the nanocrystals with both a GaN and ZnS shell significantly increases air stability and emission quantum yields. A proof‐of‐principle indium zinc nitride nanocrystal light emitting diode is also demonstrated. This work overcomes the significant challenges that have prevented the full exploration of nitride‐based semiconductor nanocrystal development, providing a new system for further exploration as a heavy‐metal free alternative to current state‐of‐the‐art materials.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Photo‐ and Electroluminescence from Zn‐Doped InN Semiconductor Nanocrystals

Fairclough

Taylor

Smith

et al. 2020

Advanced Optical Materials

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“…71 The second piece of evidence for alloying comes from the comparison between the shell thicknesses calculated via depth profiling XPS and TEM results. 72 As an example, we take the sample with the thickest CdS shell as calculated by XPS (Fig. 3A).…”

Section: Evidence For An Alloyed Shellmentioning

confidence: 99%

The passivating effect of cadmium in PbS/CdS colloidal quantum dots probed by nm-scale depth profiling

et al. 2017

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Achieving control of the surface chemistry of colloidal quantum dots (CQDs) is essential to fully exploit their properties in solar cells, but direct measurement of the chemistry and electronic structure in the outermost atomic layers is challenging. Here we probe the surface oxidation and passivation of cation-exchanged PbS/CdS core/shell CQDs with sub nm-scale precision using synchrotron-radiation-excited depth-profiling photoemission. We investigate the surface composition of the topmost 1-2.5 nm of the CQDs as a function of depth, for CQDs of varying CdS shell thickness, and examine how the surface changes after prolonged air exposure. We demonstrate that the Cd is localized at the surface of the CQDs. The surface-localized products of oxidation are identified, and the extent of oxidation quantified. We show that oxidised sulfur species are progressively eliminated as Cd replaces Pb at the surface. A sub-monolayer surface 'decoration' of Cd is found to be effective in passivating the CQDs. We show that the measured energy-level alignments at PbS/CdS colloidal quantum dot surfaces differ from those expected on the basis of bulk band offsets, and are strongly affected by the oxidation products. We develop a model for the passivating action of Cd. The optimum shell thickness (of around 0.1 nm, previously found to give maximised power conversion efficiency in PbS/CdS solar cells) is found to correspond to a trade-off between the rate of oxidation and the introduction of a surface barrier to charge transport.

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“…CdS shells have also been shown (using XPS) to stabilize InP CQDs and improve the QY and efficiency of multiple exciton generation by passivating surface traps . Another example of depth‐profiling XPS illuminating the passivating action of a surface treatment is in chloride‐treated CdTe CQDs .…”

Section: Studies Of Oxidation and Passivationmentioning

confidence: 99%

Surface and Interface Chemistry in Colloidal Quantum Dots for Solar Applications Studied by X‐Ray Photoelectron Spectroscopy

Clark

Flavell

2018

The Chemical Record

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Control of the surface and interface chemistry of colloidal quantum dots (CQDs) is critical to achieving a product with good air stability and high performing optoelectronic devices. Through various surface passivation treatments, vast improvements have been made in fields such as CQD photovoltaics; however devices have not currently reached commercial standards. We show how X‐ray photoelectron spectroscopy (XPS) can provide a better understanding of exactly how surface treatments act on CQD surfaces, and the effect of surface composition on air stability and device performance.. We illustrate this with PbS‐based CQDs, using XPS to measure oxidation processes, and to quantify the composition of the topmost surface layer after different surface treatments. We also demonstrate the use of synchrotron radiation‐excited depth‐profiling XPS, a powerful technique for determining the surface composition, chemistry and structure of CQDs. This review describes our recent progress in characterization of CQD surfaces using SR‐excited depth profiling XPS and other photoemission techniques.

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Multiple Exciton Generation and Dynamics in InP/CdS Colloidal Quantum Dots

Cited by 25 publications

References 47 publications

Photo‐ and Electroluminescence from Zn‐Doped InN Semiconductor Nanocrystals

Photo‐ and Electroluminescence from Zn‐Doped InN Semiconductor Nanocrystals

The passivating effect of cadmium in PbS/CdS colloidal quantum dots probed by nm-scale depth profiling

Surface and Interface Chemistry in Colloidal Quantum Dots for Solar Applications Studied by X‐Ray Photoelectron Spectroscopy

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