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As devices approach the single-nanoparticle scale, the rational assembly of nanomaterial heterojunctions remains a persistent challenge. While optical traps can manipulate objects in three dimensions, to date, nanoscale materials have been trapped primarily in aqueous solvents or vacuum. Here, we demonstrate the use of optical traps to manipulate, align, and assemble metal-seeded nanowire building blocks in a range of organic solvents. Anisotropic radiation pressure generates an optical torque that orients each nanowire, and subsequent trapping of aligned nanowires enables deterministic fabrication of arbitrarily long heterostructures of periodically repeating bismuth-nanocrystal/germanium-nanowire junctions. Heat transport calculations, back-focal-plane interferometry, and optical images reveal that the bismuth nanocrystal melts during trapping, facilitating tip-to-tail “nanosoldering” of the germanium nanowires. These bismuth-semiconductor interfaces may be useful for quantum computing or thermoelectric applications. In addition, the ability to trap nanostructures in oxygen- and water-free organic media broadly expands the library of materials available for optical manipulation and single-particle spectroscopy.

 

Yb 3+ -Doped lead-halide perovskites (Yb 3+ :CsPb(Cl 1−x Br x ) 3 ) have emerged as unique materials combining strong, tunable broadband absorption with near-infrared photoluminescence quantum yields (PLQYs) approaching 200% at ambient temperature. These remarkable properties make Yb 3+ :CsPb(Cl 1−x Br x ) 3 an extremely promising candidate for spectral shaping in high-efficiency photovoltaic devices. Previous theoretical assessments of such “downconversion” devices have predicted single-junction efficiencies up to 40%, but have been highly idealized. Real materials like Yb 3+ :CsPb(Cl 1−x Br x ) 3 have practical limitations such as constrained band-gap and PL energies, non-directional emission, and an excitation-power-dependent PLQY. Hence, it is unclear whether Yb 3+ :CsPb(Cl 1−x Br x ) 3 , or any other non-ideal quantum-cutting material, can indeed boost the efficiencies of real high-performance PV. Here, we examine the thermodynamic, detailed-balance efficiency limit of Yb 3+ :CsPb(Cl 1−x Br x ) 3 on different existing PV under real-world conditions. Among these, we identify silicon heterojunction technology as very promising for achieving significant performance gains when paired with Yb 3+ :CsPb(Cl 1−x Br x ) 3 , and we predict power-conversion efficiencies of up to 32% for this combination. Surprisingly, PL saturation does not negate the improved device performance. Calculations accounting for actual hourly incident solar photon fluxes show that Yb 3+ :CsPb(Cl 1−x Br x ) 3 boosts power-conversion efficiencies at all times of day and year in two representative geographic locations. Predicted annual energy yields are comparable to those of tandem perovskite-on-silicon technologies, but without the need for current matching, tracking, or additional electrodes and inverters. In addition, we show that band-gap optimization in real quantum cutters is inherently a function of their PLQY and the ability to capture that PL. These results provide key design rules needed for development of high-efficiency quantum-cutting photovoltaic devices based on Yb 3+ :CsPb(Cl 1−x Br x ) 3 .