Photoconductivity Enhancement in Multilayers of CdSe and CdTe Quantum Dots

Talgorn, Elise; Vries, M.A. de; Siebbeles, Laurens D. A.; Houtepen, Arjan J.

doi:10.1021/nn2009134

Cited by 38 publications

(34 citation statements)

References 38 publications

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“…NC organization, film uniformity, and film thickness have the potential to be tuned by varying the solvent, NC concentration, substrate surface treatment, and withdrawal speed. Dip‐coating has been utilized previously for deposition of high‐quality NC‐based electronics, but the work to date that explores dip‐coating as a method for control over NC superlattice assembly is limited . Here, we demonstrate that dip‐coating can be used to deposit ordered, polycrystalline superlattices of a variety of NC materials over 4 in (100 mm) wafer scales.…”

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Deposition of Wafer‐Scale Single‐Component and Binary Nanocrystal Superlattice Thin Films Via Dip‐Coating

et al. 2015

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thickness have the potential to be tuned by varying the solvent, NC concentration, substrate surface treatment, and withdrawal speed. Dip-coating has been utilized previously for deposition of high-quality NC-based electronics, [26][27][28][29][30] but the work to date that explores dip-coating as a method for control over NC superlattice assembly is limited. [ 31,32 ] Here, we demonstrate that dipcoating can be used to deposit ordered, polycrystalline superlattices of a variety of NC materials over 4 in (100 mm) wafer scales. We show that fi lm thickness can be controlled by varying the withdrawal speed to deposit fi lms from sub-monolayer to several multilayers. The combination of transmission electron microscopy (TEM), scanning electron microscopy (SEM), and grazing incidence small-angle X-ray scattering (GISAXS) shows that the ordered superlattice structure observed at the nanoscale by microscopy extends over the entire dip-coated area. Finally, we present the fi rst demonstration that NC assembly via dipcoating can be extended to form several binary NC superlattices (BNSLs) including AlB 2 , NaZn 13 , CaCu 5 , and MgZn 2 structures, exhibiting the versatility of dip-coating for depositing a variety of NC materials and superlattice structures.Lead selenide (PbSe) [ 33,34 ] was chosen as the pilot material for optimizing the dip-coating conditions because of its particularly narrow size distribution. Different dispersing solvents and substrate treatments commonly used in NC deposition were explored (see Section S1.1 and S1.2 of the Supporting Information). We focused primarily on assemblies deposited from toluene dispersions, which were found to favorably wet n-octyltriethoxysilane (OTS)-treated surfaces, facilitating longrange, planar order. Additionally, we studied how dip-coating withdrawal speed affects the fi lm thickness and coverage on the substrate. Figure 1 shows a series of PbSe NC thin fi lms deposited by dip-coating from a NC solution in toluene onto OTS-treated substrates at withdrawal rates of 1, 5, 15, 25, 50, and 100 mm min -1 . The 100 mm min -1 withdrawal rate is rapid in comparison to typical dip-coating processes. The fi lm color shows the optical uniformity and the color change refl ects thickness-dependent interference as the fi lms become thicker at increasing withdrawal speeds (Figure 1 a), which is quantifi ed by a shift in the energy of the fi lm refl ectance spectrum (Figure 1 b). The proportional relationship of withdrawal speed to fi lm thickness is likely due to higher withdrawal speeds wicking up a thicker solvent fi lm along the substrate surface. The slowest withdrawal speed of 1 mm min -1 , is an exception to this trend and results in a fi lm thicker than that formed at 5 mm min -1 . At the slowest withdrawal rates, the solvent evaporates across the substrate faster than the withdrawal speed as illustrated in Figure 1 c. Atomic force microscopy (AFM) ( Figure S1, Supporting Information) measurements were performed to analyze Monodisperse nanocrystals (NCs) provide an opportuni...

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Deposition of Wafer‐Scale Single‐Component and Binary Nanocrystal Superlattice Thin Films Via Dip‐Coating

et al. 2015

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“…Currently, CdSe NCs as the workhorse have been well developed for such uses 16–32. Despite their apparent advantages (high emission quantum yields, narrow emission line width, good photostability, etc 33–3738, 39.…”

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Full Visible Range Covering InP/ZnS Nanocrystals with High Photometric Performance and Their Application to White Quantum Dot Light‐Emitting Diodes

et al. 2012

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High‐quality InP/ZnS core–shell nanocrystals with luminescence tunable over the entire visible spectrum have been achieved by a facile one‐pot solvothermal method. These nanocrystals exhibit high quantum yields (above 60%), wide emission spectrum tunability and excellent photostability. The FWHM can be as narrow as 38 nm, which is close to that of CdSe nanocrystals. Also, making use of these nanocrystals, we further demonstrated a cadmium‐free white QD‐LED with a high color rendering index of 91. The high‐performance of the resulting InP/ZnS NCs coupled with their low intrinsic toxicity may further promote industrial applications of these NC emitters.

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“…Numerous research groups have worked to quantify these limitations, and consistently arrived at a similar conclusion: major further quantitative improvements in electronic transport are required to continue rapid progress for the field. [14,17,18,[31][32][33][34][35][36] Improved electronic transport must include, but also go well beyond, reporting higher carrier mobilities for charges of each type. Only once lifetime, determined by the presence of recombination centers, is also dramatically improved, can the sum of the diffusion length and drift length become comparable to, and ultimately exceed, the absorption length for light of all solar wavelengths of interest.…”

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Materials processing strategies for colloidal quantum dot solar cells: advances, present-day limitations, and pathways to improvement

et al. 2013

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Colloidal quantum dot photovoltaic devices have improved from initial, sub-1% solar power conversion efficiency to current record performance of over 7%. Rapid advances in materials processing and device physics have driven this impressive performance progress. The highestefficiency approaches rely on a fabrication process that starts with nanocrystals in solution, initially capped with long organic molecules. This solution is deposited and the resultant film is treated using a solution containing a second, shorter capping ligand, leading to a cross-linked, non-redispersible, and dense layer. This procedure is repeated, leading to the widely employed layer-by-layer solid-state ligand exchange. We will review the properties and features of this process, and will also discuss innovative pathways to creating even higher-performing films and photovoltaic devices.The most abundant and cleanest source of energy available on Earth, solar energy, is also the most underutilized. Its peak intensity is 1000 W/m 2 which, averaged over space and time, provides vastly more energy daily than the global population consumes. Solar energy thus offers, in principle, a compelling option to power a sustainable and increasingly electricitycentric future.[1] While a substantial photovoltaic industry is beginning to take shape worldwide, driven by early generation solar technology based on silicon and compound semiconductors such as cadmium telluride, the fact remains that, in order to compete with traditional energy sources, particularly with cheap and plentiful natural gas, solar photovoltaic systems must cost, fully installed, no more than $1 per watt-peak, which translates to a levelized cost of electricity of approximately $0.05/kWh over a system lifetime.[2] This is noticeably less than current first-and second-generation commercially available solar products, which are held back by higher materials and manufacturing costs; combined with installation costs influenced by the bulky, heavy, and rigid nature of the solar panels themselves.Third-generation photovoltaic systems, including organic, dye-sensitized, and colloidal quantum dot (CQD) solar cells, offer a path to low-weight, low-cost, and prospectively highefficiency solar energy capture and conversion. While thirdgeneration technologies currently function at lower efficiency than commercial first-generation modules, significant pathways exist to reach and surpass the conversion efficiencies required to be commercially feasible.CQD solar cells are of particular interest among the mentioned technologies due to the size tunability of these nanometer-scale semiconductor particles, pictured in Fig. 1(a). The optimal bandgap for a single-junction solar cell as reported by Shockley and Queisser [4] is 1.1 eV; while this offers a limited selection of bulk semiconductors, the quantum confinement effect allows the fabrication of quantum dots (QDs) with reasonable properties [5] using bulk small bandgap semiconductor compounds such as lead sulfide (PbS) and lead selenide (PbSe)...

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Photoconductivity Enhancement in Multilayers of CdSe and CdTe Quantum Dots

Cited by 38 publications

References 38 publications

Deposition of Wafer‐Scale Single‐Component and Binary Nanocrystal Superlattice Thin Films Via Dip‐Coating

Deposition of Wafer‐Scale Single‐Component and Binary Nanocrystal Superlattice Thin Films Via Dip‐Coating

Full Visible Range Covering InP/ZnS Nanocrystals with High Photometric Performance and Their Application to White Quantum Dot Light‐Emitting Diodes

Materials processing strategies for colloidal quantum dot solar cells: advances, present-day limitations, and pathways to improvement

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