Using photoluminescence (PL) spectroscopy we investigate the radiative recombination pathways in PbS quantum dots (QDs) synthesized by two methods. We compare conventionally synthesized PbS from a ...PbO precursor to PbS synthesized using cation-exchange from CdS QDs. We show that strongly coupled films of PbS QDs from the cation-exchange luminesce with significant efficiency at room temperature. This is in stark contrast to conventional PbS QDs, which have exceedingly weak room temperature emission. Furthermore, the power dependence of the emission is quadratic, indicating bimolecular radiative recombination that is reasonably competitive with trap-assisted recombination, a feature previously unreported in coupled PbS QD films. We interpret these results in terms of a greatly reduced defect concentration for cation-exchanged QDs that mitigates the influence of trap-assisted recombination. Cation-exchanged QDs have recently been employed in highly efficient and air-stable lead chalcogenide QD devices, and the reduced number of trap states inferred here may lead to improved current collection and higher open circuit voltage.
We explored the uptake of metal chloride salts with +1 to +3 metals of Na+, K+, Zn2+, Cd2+, Sn2+, Cu2+, and In3+ by PbSe QD solar cells. We also compared CdCl2 to Cd acetate and Cd nitrate ...treatments. PbSe QD solar cells fabricated with a CdCl2 treatment are stable for more than 270 days stored in air. We studied how temperature and immersion times affect optoelectronic properties and photovoltaic cell performance. Uptake of Cd2+ and Zn2+ increase open circuit voltage, whereas In3+ and K+ increase the photocurrent without influencing the spectral response or first exciton peak position. Using the most beneficial treatments we varied the bandgap of PbSe QD solar cells from 0.78 to 1.3 eV and find the improved VOC is more prevalent for lower bandgap QD solar cells.
Declining trends of civic engagement, low electoral turnout, declining confidence in public institutions, and a general lack of trust in elected officials and political parties are sentiments that ...have affected political engagement (Ekman & Amnå, 2012). Furthermore, different citizen groups have historically politically participated at various levels; men more than women and Whites more than Blacks (Robnett & Bany, 2011; Krogstad &Lopez 2017). However, research is still inadequate relating to the confluence of other psychological underpinnings - personality - along with demographics relating to political participation. This explanatory correlational study examined race, gender, education, and personality traits (independent variables) that influence political participation (dependent variable) on the 2012 presidential election. Secondary analysis of the American National Election Studies data was employed, utilizing chi-square and regression models to explain the extent to which demographic and personality variables explain political participation. Statistically significant relationships were found between political participation, race, gender, education, and personality variables. Results from this study can be useful to public officials and community leaders who advocate for political participation, strategically identify and target groups to engage in the political process.
Maintaining a stable phase
For solar cell applications, all-inorganic perovskite phases could be more stable than those containing organic cations. But the band gaps of the former, which determine ...the electrical conductivity of these materials, are not well matched to the solar spectrum. The cubic structure of CsPbI
3
is an exception, but it is stable in bulk only at high temperatures. Swarnkar
et al.
show that surfactant-coated α-CsPbI
3
quantum dots are stable at ambient conditions and have tunable band gaps in the visible range. Thin films of these materials can be made by spin coating with an antisolvent technique to minimize surfactant loss. When used in solar cells, these films have efficiencies exceeding 10%, making them promising for light harvesting or for LEDs.
Science
, this issue p.
92
The cubic crystalline phase of CsPbI
3
, which has a more favorable band gap for solar cells, is stabilized as a nanomaterial.
We show nanoscale phase stabilization of CsPbI
3
quantum dots (QDs) to low temperatures that can be used as the active component of efficient optoelectronic devices. CsPbI
3
is an all-inorganic analog to the hybrid organic cation halide perovskites, but the cubic phase of bulk CsPbI
3
(α-CsPbI
3
)—the variant with desirable band gap—is only stable at high temperatures. We describe the formation of α-CsPbI
3
QD films that are phase-stable for months in ambient air. The films exhibit long-range electronic transport and were used to fabricate colloidal perovskite QD photovoltaic cells with an open-circuit voltage of 1.23 volts and efficiency of 10.77%. These devices also function as light-emitting diodes with low turn-on voltage and tunable emission.
Here, we developed a single step, cation-exchange reaction that produces air-stable PbSe quantum dots (QDs) from ZnSe QDs and PbX2 (X = Cl, Br, or I) precursors. The resulting PbSe QDs are terminated ...with halide anions and contain residual Zn cations. We characterized the PbSe QDs using UV–vis–NIR absorption, photoluminescence quantum yield spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Solar cells fabricated from these PbSe QDs obtained an overall best power conversion efficiency of 6.47% at one sun illumination. The solar cell performance without encapsulation stays unchanged for over 50 days in ambient conditions; and after 50 days, the National Renewable Energy Laboratory certification team certified the device at 5.9%.
Perovskite solar cells deliver high efficiencies, but are often made from high‐cost bespoke chemicals, such as the archetypical hole‐conductor, ...2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxy‐phenylamine)‐9‐9′‐spirobifluorene (spiro‐OMeTAD). Herein, new charge‐transporting carbazole‐based enamine molecules are reported. The new hole conductors do not require chemical oxidation to reach high power conversion efficiencies (PCEs) when employed in n‐type‐intrinsic‐p‐type perovskite solar cells; thus, reducing the risk of moisture degrading the perovskite layer through the hydrophilicity of oxidizing additives that are typically used with conventional hole conductors. Devices made with these new undoped carbazole‐based enamines achieve comparable PCEs to those employing doped spiro‐OMeTAD, and greatly enhanced stability under 85 °C thermal aging; maintaining 83% of their peak efficiency after 1000 h, compared with spiro‐OMeTAD‐based devices that degrade to 26% of the peak PCE within 24 h. Furthermore, the carbazole‐based enamines can be synthesized without the use of organometallic catalysts and complicated purification techniques, lowering the material cost by one order of magnitude compared with spiro‐OMeTAD. As a result, we calculate that the overall manufacturing costs of future photovoltaic (PV) modules are reduced, making the levelized cost of electricity competitive with silicon PV modules.
Perovskite solar cells deliver high efficiencies, but are often made from high‐cost bespoke chemicals, such as the archetypical hole‐conductor, 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxy‐phenylamine)‐9‐9′‐spirobifluorene, spiro‐OMeTAD. In this work, new charge‐transporting carbazole‐based enamine molecules are reported.
All‐inorganic perovskite materials are attractive alternatives to organic–inorganic perovskites because of their potential for higher thermal stability. Although CsPbI
3
is compositionally stable ...under elevated temperatures, the cubic perovskite α‐phase is thermodynamically stable only at >330 °C and the low‐temperature perovskite γ‐phase is metastable and highly susceptible to non‐perovskite δ‐phase conversion in moisture. Many methods have been reported which show that the incorporation of acid (aqueous HI) or “HPbI
3
”—recently shown to be dimethylammonium lead iodide (DMAPbI
3
) —lowers the annealing temperature required to produce the black, perovskite phase of CsPbI
3
. Herein, the optical and crystallographic data presented show that dimethylammonium (DMA) can successfully incorporate as an A‐site cation to replace Cs in the CsPbI
3
perovskite material. This describes the stabilization and lower phase transition temperature reported in the literature when HI or HPbI
3
is used as precursors for CsPbI
3
. The Cs–DMA alloy only forms a pure‐phase material up to ≈25% DMA; at higher concentrations, the CsPbI
3
and DMAPbI
3
begin to phase segregate. These alloyed materials are more stable to moisture than neat CsPbI
3
, but do not represent a fully inorganic perovskite material.
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