Suchergebnisse

Colloidal lead chalcogenide quantum dots (CQDs) exhibit promising optoelectronic properties for applications in solar cell devices and as thermoelectrics. Herein, we report and discuss a ferroelectric structural distortion, at the picometer scale resolution, in PbS CQDs prepared using both classic and new synthetic pathways. The investigation was performed using synchrotron X-ray total scattering data and advanced methods of analysis that rely on a homo-core-shell model and evaluate the atomic arrangement, stoichiometry, size and morphology of nanocrystals. The CQDs show comparable size-dependent relative elongation, up to 0.7 % of one body diagonal of the cubic rock-salt structure, which corresponds to a rhombohedral lattice deformation. The findings suggest a joint role for the oleate ligands (which induce surface tensile strain) and the Pb(II) lone pair as the driving forces of the deformation. Pb displacements along the [111] direction, which provoke a ferrolectric distortion related to the lattice change, fall in the 0.0 – 0.1 Å range. Overall, the findings suggest the local nature of the metal off-centering, leading to different average displacements which depend on the synthetic conditions. ; F.B. acknowledges the European Union and the Aarhus Institute of Advanced Studies (Aarhus University) for the Marie Skłodowska-Curie AIAS-COFUND grant (EU-FP7 program, Grant Agreement No. 609033). S.J.L.B. was supported by NSF MRSEC/Columbia program (Center for Precision Assembly of Superstratic and Superatomic Solids, DMR-1420634). The technical staff of the X04SA-MS Beamline of the Swiss Light Source (PSI, Villigen, CH) is gratefully acknowledged. The measurements for PDF were Chem2, 2018, 2-1 12 conducted at NSLS II, a U.S. Department of Energy Office of Science User Facility operated by Brookhaven National Laboratory (Contract No. DE-SC0012704).

Thin-film solar cells based on hybrid lead halide perovskites have achieved certified power conversion efficiencies exceeding 24%, approaching those of crystalline silicon. This motivates deeper studies of the mechanisms that determine their performance. Twin defect sites have been proposed as a source of traps in perovskites, yet their origin and influence on photovoltaic performance remain unclear. It is found that twin defects-observed herein via both transmission electron microscopy and X-ray diffraction-are correlated with the amount of antisolvent added to the perovskite and that twin defects in the highest-performing perovskite photovoltaics are suppressed. Heterogeneous supersaturation nucleation is discussed as a contributor to efficient perovskite-based optoelectronic devices. ; The authors thank the Ministry of Science and Technology of Taiwan for support of this research (MOST 106‐2917‐I‐564‐007 and MOST 107‐2221‐E‐007‐055‐MY3). This publication is based in part on work supported by the US Department of the Navy, Office of Naval Research (Grant Award No. N00014‐17‐1‐2524), the Ontario Research Fund – Research Excellence Program, and the Natural Sciences and Engineering Research Council (NSERC) of Canada. M.I.S. acknowledges the support of the Banting Postdoctoral Fellowship Program, administered by the Government of Canada.

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. ; This work was supported by Ontario Research Fund–Research Excellence program (ORF7—Ministry of Research and Innovation, Ontario Research Fund–Research Excellence Round 7), and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2017R1A2B2009948).

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. ; This work was supported by Ontario Research Fund–Research Excellence program (ORF7—Ministry of Research and Innovation, Ontario Research Fund–Research Excellence Round 7), and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF- 2017R1A2B2009948). The authors acknowledge the financial support from QD Solar Inc.

As crystalline silicon solar cells approach in efficiency their theoretical limit, strategies are being developed to achieve efficient infrared energy harvesting to augment silicon using solar photons from beyond its 1100 nm absorption edge. Herein we report a strategy that uses multi-bandgap lead sulfide colloidal quantum dot (CQD) ensembles to maximize short-circuit current and open-circuit voltage simultaneously. We engineer the density of states to achieve simultaneously a large quasi-Fermi level splitting and a tailored optical response that matches the infrared solar spectrum. We shape the density of states by selectively introducing larger-bandgap CQDs within a smaller-bandgap CQD population, achieving a 40 meV increase in open-circuit voltage. The near-unity internal quantum efficiency in the optimized multi-bandgap CQD ensemble yielded a maximized photocurrent of 3.7 ± 0.2 mA cm-2. This provides a record for silicon-filtered power conversion efficiency equal to one power point, a 25% (relative) improvement compared to the best previously-reported results. ; This work was supported by Ontario Research Fund-Research Excellence program (ORF7-Ministry of Research and Innovation, Ontario Research Fund-Research Excellence Round 7), and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. M.I.S. acknowledges the support of the Banting Postdoctoral Fellowship Program, administered by the Government of Canada.