The performance of perovskite solar cells with inverted polarity ( p-i-n ) is still limited by recombination at their electron extraction interface, which also lowers the power conversion efficiency (PCE) of p-i-n perovskite-silicon tandem solar cells. A ~1 nm thick MgF x interlayer at the perovskite/C 60 interface through thermal evaporation favorably adjusts the surface energy of the perovskite layer, facilitating efficient electron extraction, and displaces C 60 from the perovskite surface to mitigate nonradiative recombination. These effects enable a champion V oc of 1.92 volts, an improved fill factor of 80.7%, and an independently certified stabilized PCE of 29.3% for a ~1 cm 2 monolithic perovskite-silicon tandem solar cell. The tandem retained ~95% of its initial performance following damp-heat testing (85 Celsius at 85% relative humidity) for > 1000 hours.

Arrays of mesoporous manganese dioxide, mp-MnO(2), nanowires were electrodeposited on glass and silicon surfaces using the lithographically patterned nanowire electrodeposition (LPNE) method. The electrodeposition procedure involved the application, in a Mn(ClO(4))(2)-containing aqueous electrolyte, of a sequence of 0.60 V (vs MSE) voltage pulses delineated by 25 s rest intervals. This "multipulse" deposition program produced mp-MnO(2) nanowires with a total porosity of 43-56%. Transmission electron microscopy revealed the presence within these nanowires of a network of 3-5 nm diameter fibrils that were X-ray and electron amorphous, consistent with the measured porosity values. mp-MnO(2) nanowires were rectangular in cross-section with adjustable height, ranging from 21 to 63 nm, and adjustable width ranging from 200 to 600 nm. Arrays of 20 nm × 400 nm mp-MnO(2) nanowires were characterized by a specific capacitance, C(sp), of 923 ± 24 F/g at 5 mV/s and 484 ± 15 F/g at 100 mV/s. These C(sp) values reflected true hybrid electrical energy storage with significant contributions from double-layer capacitance and noninsertion pseudocapacitance (38% for 20 nm × 400 nm nanowires at 5 mV/s) coupled with a Faradaic insertion capacity (62%). These two contributions to the total C(sp) were deconvoluted as a function of the potential scan rate.

We describe the fabrication of arrays of nanowires on glass in which a gold core nanowire is encapsulated within a hemicylindrical shell of manganese dioxide. Arrays of linear gold (Au) nanowires are first prepared on glass using the lithographically patterned nanowire electrodeposition (LPNE) method. These Au nanowires have a rectangular cross-section with a width and height of ≈200 and 40 nm, respectively, and lengths in the 1 mm to 1 cm range. Au nanowires are then used to deposit MnO2 by potentiostatic electrooxidation from Mn2+ solution, forming a conformal, hemicylindrical shell with a controllable diameter ranging from 50 to 300 nm surrounding each Au nanowire. This MnO2 shell is δ-phase and mesoporous, as revealed by X-ray diffraction and Raman spectroscopy. Transmission electron microscopy (TEM) analysis reveals that the MnO2 shell is mesoporous (mp-MnO2), consisting of a network of ≈2 nm fibrils. The specific capacitance, C sp , of arrays of gold:mp-MnO2 nanowires is measured using cyclic voltammetry. For a mp-MnO2 shell thickness of 68 ± 3 nm, core:shell nanowires produce a C sp of 1020 ± 100 F/g at 5 mV/s and 450 ± 70 F/g at 100 mV/s. The cycle stability of this C sp , however, is extremely limited in aqueous electrolyte, decaying by >90% in 100 scans, but after oven drying and immersion in dry 1.0 M LiClO4, acetonitrile, dramatically improved cycle stability is achieved characterized by the absence of C sp fade for 1000 cycles at 100 mV/s. Core:shell nanowires exhibit true hybrid energy storage, as revealed by deconvolution of C sp into insertion and noninsertion components.

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Perovskite solar cells (PSCs) based on 2D/3D heterostructures show great potential to combine the advantages of the high efficiency of 3D perovskites and the high stability of 2D perovskites. However, an in‐depth understanding of the organic‐spacer effects on the 2D quantum well (QW) structures and electronic properties at the 2D/3D interfaces is yet to be fully achieved, especially in the case of 2D perovskites based on diammonium spacers/ligands. Here, a series of diammonium spacers is considered for the construct ion 2D/3D perovskite heterostructures. It is found that the chemical structure and concentration of the spacers can dramatically affect the characteristics of the 2D capping layers, including their phase purity and orientation. Density functional theory calculations indicate that the spacer modifications can induce shifts in the energy‐level alignments at the 2D/3D interfaces and therefore influence the charge‐transfer characteristics. The strong intermolecular interactions between the 2,2‐(ethylenedioxy)bis(ethylammonium) (EDBE) cations and inorganic [PbI6]4− slabs facilitate a controlled deposition of a phase‐pure QW structure (n = 1) with a horizontal orientation, which leads to better surface passivation and carrier extraction. These benefits endow the EDBE‐based 2D/3D devices with a high power conversion efficiency of 22.6% and remarkable environmental stability, highlighting the promise of spacer‐chemistry design for high‐performance 2D/3D PSCs.

A symmetrical hybrid capacitor consisting of interdigitated, horizontal nanowires is described. Each of the 750 nanowires within the capacitor is 2.5 mm in length, consisting of a gold nanowire core (40 × ≈200 nm) encapsulated within a hemicylindrical shell of δ-phase MnO2 (thickness = 60-220 nm). These Au@δ-MnO2 nanowires are patterned onto a planar glass surface using lithographically patterned nanowire electrodeposition (LPNE). A power density of 165 kW/kg and energy density of 24 Wh/kg were obtained for a typical nanowire array in which the MnO2 shell thickness was 68 ± 8 nm. Capacitors incorporating these ultralong nanowires lost ≈10% of their capacity rapidly, during the first 20 discharge cycles, and then retained 90% of their maximum capacity for the ensuing 6000 cycles. The ability of capacitors consisting of ultralong Au@δ-MnO2 nanowires to simultaneously deliver high power and high capacity with acceptable cycle life is demonstrated.

Nanocrystalline cadmium selenide (nc-CdSe) was electrodeposited within a sub-50 nm gold nanogap, prepared by feedback-controlled electromigration, to form a photoconductive metal-semiconductor-metal nanojunction. Both gap formation and electrodeposition were rapid and automated. The electrodeposited nc-CdSe was stoichiometric, single cubic phase with a mean grain diameter of ∼7 nm. Optical absorption, photoluminescence, and the spectral photoconductivity response of the nc-CdSe were all dominated by band-edge transitions. The photoconductivity of these nc-CdSe-filled gold nanogaps was characterized by a detectivity of 6.9 × 10(10) Jones and a photosensitivity of 500. These devices also demonstrated a maximum photoconductive gain of ∼45 and response and recovery times below 2 μs, corresponding to a 3 dB bandwidth of at least 175 kHz.

Electroluminescent (EL) metal-semiconductor-metal nanojunctions are prepared by electrodepositing nanocrystalline cadmium selenide (nc-CdSe) within ∼250 nm gold (Au) nanogaps prepared by focused ion beam milling. The electrodeposition of nc-CdSe is carried out at two temperatures: 20 °C (“cold”) and 75 °C (“hot”), producing mean grain diameters of 6 ± 1 nm and 11 ± 2 nm, respectively, for the nc-CdSe. Light-emitting nanojunctions (LEnJs) prepared at both temperatures show a low threshold voltage for light emission of <2 V; just above the 1.74 eV bandgap of CdSe. The EL intensity increases with the injection current and hot-deposited LEnJs produced a maximum EL intensity that is an order of magnitude higher than the cold-deposited LEnJs. Emitted photons are bimodal in energy with emission near the band gap of CdSe, and also at energies 200 meV below it; consistent with a mechanism of light emission involving the radiative recombination of injected holes with electrons at both band-edge and defect states. The quantum yield for “hot” electrodeposited nc-CdSe LEnJs is comparable to devices constructed from single crystalline nanowires of CdSe, and the threshold voltage of 1.9 (±0.1) V (cold) and 1.5 (±0.2) V (hot) is at the low end of the range reported for CdSe nanowire based devices.