Luminescent solar concentrators (LSCs) can concentrate direct and diffuse solar radiation spatially and energetically to help reduce the overall area of solar cells needed to meet current energy demands. LSCs require luminophores that absorb large fractions of the solar spectrum, emit photons into a light-capture medium with high photoluminescence quantum yields (PLQYs), and do not absorb their own photoluminescence. Luminescent nanocrystals (NCs) with near or above unity PLQYs and Stokes shifts large enough to avoid self-absorption losses are well-suited to meet these needs. In this work, we describe LSCs based on quantum-cutting Yb 3+ :CsPb(Cl 1−x Br x ) 3 NCs that have documented PLQYs as high as ∼200%. Through a combination of solution-phase 1D LSC measurements and modeling, we demonstrate that Yb 3+ :CsPbCl 3 NC LSCs show negligible intrinsic reabsorption losses, and we use these data to model the performance of large-scale 2D LSCs based on these NCs. We further propose a new and unique monolithic bilayer LSC device architecture that contains a Yb 3+ :CsPb(Cl 1−x Br x ) 3 NC top layer above a second narrower-gap LSC bottom layer ( e.g. , based on CuInS 2 NCs), both within the same waveguide and interfaced with the same Si PV for conversion. We extend the modeling to predict the flux gains of such bilayer devices. Because of the exceptionally high PLQYs of Yb 3+ :CsPb(Cl 1−x Br x ) 3 NCs, the optimized bilayer device has a projected flux gain of 63 for dimensions of 70 × 70 × 0.1 cm 3 , representing performance enhancement of at least 19% over the optimized CuInS 2 LSC alone.
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Integration of Highly Luminescent Lead Halide Perovskite Nanocrystals on Transparent Lead Halide Nanowire Waveguides through Morphological Transformation and Spontaneous Growth in Water
The integration of highly luminescent CsPbBr3quantum dots on nanowire waveguides has enormous potential applications in nanophotonics, optical sensing, and quantum communications. On the other hand, CsPb2Br5nanowires have also attracted a lot of attention due to their unique water stability and controversial luminescent property. Here, the growth of CsPbBr3nanocrystals on CsPb2Br5nanowires is reported first by simply immersing CsPbBr3powder into pure water, CsPbBr3−
- NSF-PAR ID:
- 10447375
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 18
- Issue:
- 11
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract All‐inorganic lead halide perovskite nanocrystals (NCs) have great optoelectronic properties with promising applications in light‐emitting diodes (LEDs), lasers, photodetectors, solar cells, and photocatalysis. However, the intrinsic toxicity of Pb and instability of the NCs impede their broad applications. Shell‐coating is an effective method for enhanced environmental stability while reducing toxicity by choosing non‐toxic shell materials such as metal oxides, polymers, silica, etc. However, multiple perovskite NCs can be encapsulated within the shell material and a uniform epitaxial‐type shell growth of well‐isolated NCs is still challenging. In this work, lead‐free vacancy‐ordered double perovskite Cs2SnX6(X = Cl, Br, and I) shells are epitaxially grown on the surface of CsPbX3NCs by a hot‐injection method. The effectiveness of the non‐toxic double perovskite shell protection is demonstrated by the enhanced environmental and phase stability against UV illumination and water. In addition, the photoluminescence quantum yields (PL QYs) increase for the CsPbCl3and CsPbBr3NCs after shelling because of the type I band alignment of the core/shell materials, while enhanced charge transport properties obtained from CsPbI3/Cs2SnI6core/shell NCs are due to the efficient charge separation in the type II core/shell band alignment.
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Zero-dimensional (0D) halides perovskites, in which anionic metal-halide octahedra (MX 6 ) 4− are separated by organic or inorganic countercations, have recently shown promise as excellent luminescent materials. However, the origin of the photoluminescence (PL) and, in particular, the different photophysical properties in hybrid organic–inorganic and all inorganic halides are still poorly understood. In this work, first-principles calculations were performed to study the excitons and intrinsic defects in 0D hybrid organic–inorganic halides (C 4 N 2 H 14 X) 4 SnX 6 (X = Br, I), which exhibit a high photoluminescence quantum efficiency (PLQE) at room temperature (RT), and also in the 0D inorganic halide Cs 4 PbBr 6 , which suffers from strong thermal quenching when T > 100 K. We show that the excitons in all three 0D halides are strongly bound and cannot be detrapped or dissociated at RT, which leads to immobile excitons in (C 4 N 2 H 14 X) 4 SnX 6 . However, the excitons in Cs 4 PbBr 6 can still migrate by tunneling, enabled by the resonant transfer of excitation energy (Dexter energy transfer). The exciton migration in Cs 4 PbBr 6 leads to a higher probability of trapping and nonradiative recombination at the intrinsic defects. We show that a large Stokes shift and the negligible electronic coupling between luminescent centers are important for suppressing exciton migration; thereby, enhancing the photoluminescence quantum efficiency. Our results also suggest that the frequently observed bright green emission in Cs 4 PbBr 6 is not due to the exciton or defect-induced emission in Cs 4 PbBr 6 but rather the result of exciton emission from CsPbBr 3 inclusions trapped in Cs 4 PbBr 6 .more » « less
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Abstract The all‐inorganic metal halide perovskite CsPbX3(X = Cl, Br, and I) has received extensive attention in the field of white light‐emitting diodes (WLEDs) due to its high luminous intensity and high color purity. However, the shortcoming of poor stability directly affects the luminous performance of the WLED devices and reduces their luminous efficiency, which has become an urgent problem to be solved. Here, three‐color lead halide perovskite phosphors (blue‐emitting CsPbBr3synthesized at 20 °C (CPB‐20), green‐emitting CsPbBr3‐80 (CPB‐80)/CsPbBr3:SCN−(CPB:SCN−), and red‐emitting PEA2PbBr4(PPB)/PEA2PbBr4:Mn2+(PPB:Mn2+)) with higher stability and luminous intensity are simultaneously prepared and applied in WLEDs. Density functional theory is used to optimize the structures of CsPbBr3and PEA2PbBr4, and to calculate the work function, optical properties, and charge density difference. Not only the WLED devices with three‐color lead halide perovskite phosphors are constructed, but also WLED devices from warm white to cold white are realized by tuning the ratio of the different emissions, and a superior color quality (color rendering index of 96) and ideal correlated color temperature (CCT of 9376 K) are achieved. This work will set the stage for exploring low‐cost, environmentally friendly, high‐performance WLEDs.
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Abstract To evaluate the role of planar defects in lead‐halide perovskites—cheap, versatile semiconducting materials—it is critical to examine their structure, including defects, at the atomic scale and develop a detailed understanding of their impact on electronic properties. In this study, postsynthesis nanocrystal fusion, aberration‐corrected scanning transmission electron microscopy, and first‐principles calculations are combined to study the nature of different planar defects formed in CsPbBr3nanocrystals. Two types of prevalent planar defects from atomic resolution imaging are observed: previously unreported Br‐rich [001](210)∑5 grain boundaries (GBs) and Ruddlesden–Popper (RP) planar faults. The first‐principles calculations reveal that neither of these planar faults induce deep defect levels, but their Br‐deficient counterparts do. It is found that the ∑5 GB repels electrons and attracts holes, similar to an n–p–n junction, and the RP planar defects repel both electrons and holes, similar to a semiconductor–insulator–semiconductor junction. Finally, the potential applications of these findings and their implications to understand the planar defects in organic–inorganic lead‐halide perovskites that have led to solar cells with extremely high photoconversion efficiencies are discussed.
