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Achieving high solar-to-hydrogen (STH) efficiency concomitant with long-term durability using low-cost, scalable photo-absorbers is a long-standing challenge. Here we report the design and fabrication of a conductive adhesive-barrier (CAB) that translates >99% of photoelectric power to chemical reactions. The CAB enables halide perovskite-based photoelectrochemical cells with two different architectures that exhibit record STH efficiencies. The first, a co-planar photocathode-photoanode architecture, achieved an STH efficiency of 13.4% and 16.3 h to t60, solely limited by the hygroscopic hole transport layer in the n-i-p device. The second was formed using a monolithic stacked silicon-perovskite tandem, with a peak STH efficiency of 20.8% and 102 h of continuous operation before t60 under AM 1.5G illumination. These advances will lead to efficient, durable, and low-cost solar-driven water-splitting technology with multifunctional barriers. High-efficiency photoelectrodes, which integrate light absorption with catalysis, have been limited to costly materials. Here, the authors develop an anticorrosion barrier that enables low-cost semiconductors for integrated solar fuel devices with 20.8% solar-to-hydrogen energy conversion efficiency. [ABSTRACT FROM AUTHOR]

Field-effect transistors based on individual carbon nanotubes with reduced Schottky barriers are studied up to pressures of 0.9 GPa and down to temperatures of less than 10 K. At ambient temperature and high pressure, complex effects are observed in a small bundle of tubes stemming from either the intrinsic modifications of the nanotubes at their ovalization, the evolution of barriers at the tube/electrodes contacts, or even both processes. Variations of the nanotube transport characteristics related to changes in the tube environment are most possibly also involved. Despite the highly complex pressure induced changes occurring in our device, low temperature measurements (<10 K) at high pressure (4.5 kbar) provide the first experimental evidence of Coulomb blockade at high pressure and the conservation of the ballistic behaviour of charges carriers in nanotubes under important stress-induced strain. [ABSTRACT FROM AUTHOR]

Electron sources are a critical component in a wide range of applications such as electron-beam accelerator facilities, photomultipliers, and image intensifiers for night vision. We report efficient, regenerative and low-cost electron sources based on solution-processed halide perovskites thin films when they are excited with light with energy equal to or above their bandgap. We measure a quantum efficiency up to 2.2% and a lifetime of more than 25 h. Importantly, even after degradation, the electron emission can be completely regenerated to its maximum efficiency by deposition of a monolayer of Cs. The electron emission from halide perovskites can be tuned over the visible and ultraviolet spectrum, and operates at vacuum levels with pressures at least two-orders higher than in state-of-the-art semiconductor electron sources. Electron sources play as important component in a wide range of applications. Here, the authors demonstrate efficient, regenerative, and low-cost electron sources based on solution-processed halide perovskite thin films with quantum efficiency up to 2.2% and a lifetime of more than 25 h. [ABSTRACT FROM AUTHOR]

In the fast-evolving field of halide perovskite semiconductors, the 2D perovskites (A′)2(A)n-1MnX3n+1 [where A = Cs+, CH3NH3 +, HC(NH2)2 +; A′ = ammonium cation acting as spacer; M = Ge2+, Sn2+, Pb2+; and X = Cl-, Br-, I-] have recently made a critical entry. The n value defines the thickness of the 2D layers, which controls the optical and electronic properties. The 2D perovskites have demonstrated preliminary optoelectronic device lifetime superior to their 3D counterparts. They have also attracted fundamental interest as solution-processed quantum wells with structural and physical properties tunable via chemical composition, notably by the n value defining the perovskite layer thickness. The higher members (n > 5) have not been documented, and there are important scientific questions underlying fundamental limits for n. To develop and utilize these materials in technology, it is imperative to understand their thermodynamic stability, fundamental synthetic limitations, and the derived structure-function relationships. We report the effective synthesis of the highest iodide n-members yet, namely (CH3(CH2)2NH3)2(CH3NH3)5Pb6I19 (n = 6) and (CH3(CH2)2NH3)2(CH3NH3)6Pb7I22 (n = 7), and confirm the crystal structure with single-crystal X-ray diffraction, and provide indirect evidence for "(CH3(CH2)2NH3)2(CH3NH3)8Pb9I28" ("n = 9"). Direct HCl solution calorimetric measurements show the compounds with n > 7 have unfavorable enthalpies of formation (ΔHf), suggesting the formation of higher homologs to be challenging. Finally, we report preliminary n-dependent solar cell efficiency in the range of 9-12.6% in these higher n-members, highlighting the strong promise of these materials for high-performance devices. [ABSTRACT FROM AUTHOR]

State-of-the-art quantum-well-based devices such as photovoltaics, photodetectors, and light-emission devices are enabled by understanding the nature and the exact mechanism of electronic charge transport. Ruddlesden-Popper phase halide perovskites are twodimensional solution-processed quantum wells and have recently emerged as highly efficient semiconductors for solar cell approaching 14% in power conversion efficiency. However, further improvements will require an understanding of the charge transport mechanisms, which are currently unknown and further complicated by the presence of strongly bound excitons. Here, we unambiguously determine that dominant photocurrent collection is through electric field-assisted electron-hole pair separation and transport across the potential barriers. This is revealed by in-depth device characterization, coupled with comprehensive device modeling, which can self-consistently reproduce our experimental findings. These findings establish the fundamental guidelines for the molecular and device design for layered 2D perovskite-based photovoltaics and optoelectronic devices, and are relevant for other similar quantum-confined systems. [ABSTRACT FROM AUTHOR]

2D Ruddlesden-Popper (RP) perovskites have recently emerged as promising candidates for hybrid perovskite photovoltaic cells, realizing power-conversion efficiencies (PCEs) of over 10% with technologically relevant stability. To achieve solar cell performance comparable to the state-of-the-art 3D perovskite cells, it is highly desirable to increase the conductivity and lower the optical bandgap for enhanced near-IR region absorption by increasing the perovskite slab thickness. Here, the use of the 2D higher member ( n = 5) RP perovskite ( n-butyl-NH3)2(MeNH3)4Pb5I16 in depositing highly oriented thin films from dimethylformamide/dimethylsulfoxide mixtures using the hot-casting method is reported. In addition, they exhibit superior environmental stability over thin films of their 3D counterpart. These films are assembled into high-efficiency solar cells with an open-circuit voltage of ≈1 V and PCE of up to 10%. This is achieved by fine-tuning the solvent ratio, crystal growth orientation, and grain size in the thin films. The enhanced performance of the optimized devices is ascribed to the growth of micrometer-sized grains as opposed to more typically obtained nanometer grain size and highly crystalline, densely packed microstructures with the majority of the inorganic slabs preferentially aligned out of plane to the substrate, as confirmed by X-ray diffraction and grazing-incidence wide-angle X-ray scattering mapping. [ABSTRACT FROM AUTHOR]

Perovskite materials due to their exceptional photophysical properties are beginning to dominate the field of thin-film optoelectronic devices. However, one of the primary challenges is the processing-dependent variability in the properties, thus making it imperative to understand the origin of such variations. Here, it is discovered that the precursor solution aging time before it is cast into a thin film, is a subtle but a very important factor that dramatically affects the overall thin-film formation and crystallinity and therein factors such as grain growth, phase purity, surface uniformity, trap state density, and overall solar cell performance. It is shown that progressive aging of the precursor promotes efficient formation of larger seeds after the fast nucleation of a large density of small seeds. The hot-casting method then leads to the growth of large grains in uniform thin-films with excellent crystallinity validated using scanning microscopy images and X-ray diffraction patterns. The high-quality films cast from aged solution is ideal for thin-film photovoltaic device fabrication with reduced shunt current and good charge transport. This observation is a significant step toward achieving highly crystalline thin-films with reliability in device performance and establishes the subtle but dramatic effect of solution aging before fabricating perovskite thin-films. [ABSTRACT FROM AUTHOR]

Hybrid organic-inorganic perovskites have attracted considerable attention after promising developments in energy harvesting and other optoelectronic applications. However, further optimization will require a deeper understanding of the intrinsic photophysics of materials with relevant structural characteristics. Here, the dynamics of photoexcited charge carriers in large-area grain organic-inorganic perovskite thin films is investigated via confocal time-resolved photoluminescence spectroscopy. It is found that the bimolecular recombination of free charges is the dominant decay mechanism at excitation densities relevant for photovoltaic applications. Bimolecular coefficients are found to be on the order of 10−9 cm3 s−1, comparable to typical direct-gap semiconductors, yet significantly smaller than theoretically expected. It is also demonstrated that there is no degradation in carrier transport in these thin films due to electronic impurities. Suppressed electron-hole recombination and transport that is not limited by deep level defects provide a microscopic model for the superior performance of large-area grain hybrid perovskites for photovoltaic applications. [ABSTRACT FROM AUTHOR]