Morphology engineering has been recognized as an effective way to attain highly efficient and stable hybrid perovskite solar cells.

Hybrid organic-inorganic halide perovskites (HOIPs) have recently attracted tremendous attention because of their excellent semiconducting and optoelectronic properties, which exist despite their morphology and crystallinity being far inferior to those of more mature semiconductors, such as silicon and III-V compound semiconductors. Heteroepitaxy can provide a route to achieving high-performance HOIP devices when high crystalline quality and smooth morphology are required, but work on heteroepitaxial HOIPs has not previously been reported. Here, we demonstrate epitaxial growth of methylammonium lead iodide (MAPbI) on single crystal KCl substrates with smooth morphology and the highest carrier recombination lifetime (∼213 ns) yet reported for nonsingle crystalline MAPbI. Experimental Raman spectra agree well with theoretical calculations, presenting in particular a sharp peak at 290 cm for the torsional mode of the organic cations, a marker of orientational order and typically lacking in previous reports. Photodetectors were fabricated showing excellent performance, confirming the high quality of the epitaxial MAPbI thin films. This work provides a new strategy to enhance the performance of all HOIPs-based devices.

A liquid junction photoelectrochemical (PEC) solar cell based on p-type methylammonium lead iodide (p-MeNH3PbI3) perovskite with a large open-circuit voltage is developed. MeNH3PbI3 perovskite is readily soluble or decomposed in many common solvents. However, the solvent dichloromethane (CH2Cl2) can be employed to form stable liquid junctions. These were characterized with photoelectrochemical cells with several redox couples, including I3(-)/I(-), Fc/Fc(+), DMFc/DMFc(+), and BQ/BQ(•-) (where Fc is ferrocene, DMFc is decamethylferrocene, BQ is benzoquinone) in CH2Cl2. The solution-processed MeNH3PbI3 shows cathodic photocurrents and hence p-type behavior. The difference between the photocurrent onset potential and the standard potential for BQ/BQ(•-) is 1.25 V, which is especially large for a semiconductor with a band gap of 1.55 eV. A PEC photovoltaic cell, with a configuration of p-MeNH3PbI3/CH2Cl2, BQ (2 mM), BQ(•-) (2 mM)/carbon, shows an open-circuit photovoltage of 1.05 V and a short-circuit current density of 7.8 mA/cm(2) under 100 mW/cm(2) irradiation. The overall optical-to-electrical energy conversion efficiency is 6.1%. The PEC solar cell shows good stability for 5 h under irradiation.

Solar-to-fuel conversion with organic-inorganic hybrid halide perovskites has attracted growing attention as a result of their excellent optoelectronic properties as well as the low temperature of the solution based fabrication process. However, the most comprehensively developed hybrid perovskite materials are comprised of the toxic metal lead, raising concerns about environmental health threats. Herein, a lead-free bismuth (Bi)-based hybrid perovskite showing in situ growth of heterojunctions is successfully developed at the interface of methylammonium bismuth iodide (MA 3 Bi 2 I 9) and tri(dimethylammonium) hexa-iodobismuthate (DMA 3 BiI 6) by a facile solvent engineering technique. The air-stable MA 3 Bi 2 I 9 /DMA 3 BiI 6 perovskite heterostructure with enhanced photoinduced charge separation exhibit outstanding visible-light-induced photocatalytic activity for H 2 evolution in aqueous hydrogen iodide solution. The powdered MA 3 Bi 2 I 9 /DMA 3 BiI 6 heterostructured composite (BBP-5) shows a H 2 evolution rate of 198.2 µmol h −1 g −1 without the addition of Pt co-catalysts under 100 mW cm −2 of visible-light (λ ≥ 420 nm) illumination.

The rational design of photocatalysts for efficient nitrogen (N 2 ) fixation at ambient conditions is important for revolutionizing ammonia production and quite challenging because the great difficulty lies in the adsorption and activation of the inert N 2 . Inspired by a biological molecule, chlorophyll, featuring a porphyrin structure as the photosensitizer and enzyme nitrogenase featuring an iron (Fe) atom as a favorable binding site for N 2 via π-backbonding, here we developed a porphyrin-based metal−organic framework (PMOF) with Fe as the active center as an artificial photocatalyst for N 2 reduction reaction (NRR) under ambient conditions. The PMOF features aluminum (Al) as metal node imparting high stability and Fe incorporated and atomically dispersed by residing at each porphyrin ring promoting the adsorption and the activation of N 2 , termed Al-PMOF(Fe). Compared with the pristine Al-PMOF, Al-PMOF(Fe) exhibits a substantial enhancement in NH 3 yield (635 μg g −1 cat. ) and production rate (127 μg h −1 g −1 cat. ) of 82% and 50%, respectively, on par with the best-performing MOF-based NRR catalysts. Three cycles of photocatalytic NRR experimental results corroborate a stable photocatalytic activity of Al-PMOF(Fe). The combined experimental and theoretical results reveal that the Fe−N site in Al-PMOF(Fe) is the active photocatalytic center that can mitigate the difficulty of the rate-determining step in photocatalytic NRR. The possible reaction pathways of NRR on Al-PMOF(Fe) were established. Our study of porphyrin-based MOF for the photocatalytic NRR will provide insight into the rational design of catalysts for artificial photosynthesis.

Silicon-based photoelectrodes for solar fuel production have attracted great interest over the past decade, with the major challenge being silicon's vulnerability to corrosion. A metal-insulator-semiconductor architecture, in which an insulator film serves as a protection layer, can prevent corrosion but must also allow low-resistance carrier transport, generally leading to a trade-off between stability and efficiency. In this work, we propose and demonstrate a general method to decouple the two roles of the insulator by employing localized dielectric breakdown. This approach allows the insulator to be thick, which enhances stability, while enabling low-resistance carrier transport as required for efficiency. This method can be applied to various oxides, such as SiO and AlO. In addition, it is suitable for silicon, III-V compounds, and other optical absorbers for both photocathodes and photoanodes. Finally, the thick metal-oxide layer can serve as a thin-film antireflection coating, which increases light absorption efficiency.

A variety of PbI 2 /MAPbI 3 perovskites were prepared and investigated by a rapid screening technique utilizing a modified scanning electrochemical microscope (SECM) in order to determine how excess PbI 2 affects its photoelectrochemical (PEC) properties. An optimum ratio of 2.5% PbI 2 /MAPbI 3 was found to enhance photocurrent over pristine MAPbI 3 on a spot array electrode under irradiation. With bulk films of various PbI 2 /MAPbI 3 composites prepared by a spin-coating technique of mixed precursors and a one-step annealing process, the 2.5% PbI 2 /MAPbI 3 produced an increased photocurrent density compared to pristine MAPbI 3 for 2 mM benzoquinone (BQ ) reduction at −0.4 V vs Fc/Fc + . As a result of the relatively high quantum yield of MAPbI 3 , a time-resolved photoluminescence quenching experiment could be applied to determine electron−hole diffusion coefficients and diffusion lengths of PbI 2 /MAPbI 3 composites, respectively. The diffusion coefficients combined with the exciton lifetime of the pristine 2.5% PbI 2 /MAPbI 3 (τ PL = 103.3 ns) give the electron and hole exciton diffusion lengths, ∼300 nm. Thus, the 2.5% PbI 2 /MAPbI 3 led to an approximately 3.0-fold increase in the diffusion length compared to a previous report of ∼100 nm for the pristine MAPbI 3 perovskite. We then demonstrated that the efficiency of liquid-junction solar cells for 2.5% excess PbI 2 of p-MAPbI 3 was improved from 6.0% to 7.3%.

Aqueous electrochemiluminescence (ECL) in the second near-infrared biowindow (NIR-II, 900–1700 nm) was anticipated for ECL evolution and spectral multiplexing. Herein, aqueous and monochromatic ECL with a single emission peak beyond 900 nm was achieved by employing methionine (Met)-capped Au–Ag bimetallic nanoclusters (BNCs) as luminophores and triethanolamine (TEOA) as a coreactant. The Met-capped Au–Ag BNCs with surface-defect-induced PL around 756 nm were water-soluble and synthesized via doping Met-capped Au NCs with Ag in a doping-in-growth way. By extensively exploiting the red-shifting nature of surface-defect-induced ECL to PL and the synergetic-effect-enhanced ECL of BNCs, physically surface-confined Au–Ag BNCs exhibited efficient NIR-II ECL around 906 nm in aqueous medium. A spectrum-based NIR-II ECL immunoassay around 915 nm was also achieved by immobilizing the Au–Ag BNCs onto an electrode surface via forming a sandwich immunocomplex, which could selectively determine CA125 from 5 × 10–4 to 1 U/mL with a detection limit of 5 × 10–5 U/mL (S/N = 3). The combined strategy of surface-defect-induced ECL and synergetic-effect-enhanced ECL would enable promising biorelated application of NIR-II ECL.