Realizing solution-processed heterostructures is a long-enduring challenge in halide perovskites because of solvent incompatibilities that disrupt the underlying layer. By leveraging the solvent dielectric constant and Gutmann donor number, we could grow phase-pure two-dimensional (2D) halide perovskite stacks of the desired composition, thickness, and bandgap onto 3D perovskites without dissolving the underlying substrate. Characterization reveals a 3D–2D transition region of 20 nanometers mainly determined by the roughness of the bottom 3D layer. Thickness dependence of the 2D perovskite layer reveals the anticipated trends for n-i-p and p-i-n architectures, which is consistent with band alignment and carrier transport limits for 2D perovskites. We measured a photovoltaic efficiency of 24.5%, with exceptional stability of T 99 (time required to preserve 99% of initial photovoltaic efficiency) of >2000 hours, implying that the 3D/2D bilayer inherits the intrinsic durability of 2D perovskite without compromising efficiency.

Two-dimensional (2D) hybrid halide perovskites are promising in optoelectronic applications, particularly solar cells and light emitting devices (LEDs), and for their increased stability compared to 3D perovskites. Here, we report a new series of structures using propylammonium (PA +) which results in a series of Ruddlesden-Popper (RP) structures with the formula (PA) 2 (MA) n-1 Pb n I 3n+1 (n = 3, 4) and a new homologous series of "step-like" (SL) structures where the PbI 6 octahedra connect in a corner-and face-sharing motif with the general formula (PA) 2m+4 (MA) m-2 Pb 2m+1 I 7m+4 (m = 2, 3, 4). The RP structures show a blue-shift in bandgap for decreasing n (1.90 eV for n = 4 and 2.03 eV for n = 3) while the SL structures have an even greater blue-shift (2.53 eV for m = 4, 2.74 eV for m = 3, and 2.93 eV for m = 2). DFT calculations show that, while the RP structures are electronically 2D quantum wells, the SL structures are electronically 1D quantum wires with chains of corner-sharing octahedra "insulated" by blocks of face-sharing octahedra. Dark measurements for RP crystals show high resistivity perpendicular to the layers (10 11 Ω•cm) but a lower resistivity parallel to them (10 7 Ω•cm). The SL crystals have varying resistivity in all three directions, confirming both RP and SL crystals' utility as anisotropic electronic materials. The RP structures show strong photoresponse, whereas the SL materials exhibit resistivity trends that are dominated by ionic

Two-dimensional (2D) perovskites are a class of halide perovskites offering a pathway for realizing efficient and durable optoelectronic devices. However, the broad chemical phase space and lack of understanding of film formation have led to quasi-2D perovskite films with polydispersity in perovskite layer thicknesses, which have hindered devices performance and stability. Here, we demonstrate a scalable approach involving dissolution of single-phase crystalline powders with homogeneous perovskite layer thickness in desired solvents, to fabricate 2D perovskite thin-films with high phase purity. In-situ characterizations reveal the presence of sub-micron-sized seeds in solution that preserve the memory of the dissolved single-crystals and dictate the nucleation and growth of grains with identical thickness of the perovskite layers in thin-films. Photovoltaic devices fabricated with such films, yields an efficiency of 17.1% and 1.20V open-circuit voltage, while preserving 97.5% of their peakperformance after 800 hours under illumination without any external thermal management.

The performance of perovskite solar cell (PSC) is highly sensitive to deposition conditions, the substrate, humidity, and the efficiency of solvent extraction. However, the physical mechanism involved in the observed changes of efficiency with different deposition conditions has not been elucidated yet. In this work, PSCs were fabricated by the antisolvent deposition (AD) and recently proposed air-extraction antisolvent (AAD) process. Impedance analysis and J-V curve fitting were used to analyze the photogeneration, charge transportation, recombination, and leakage properties of PSCs. It can be elucidated that the improvement in morphology of perovskite film promoted by AAD method leads to increase in light absorption, reduction in recombination sites, and interstitial defects, thus enhancing the short-circuit current density, open-circuit voltage, and fill factor. This study will open up doors for further improvement of device and help in understanding its physical mechanism and its relation to the deposition methods.

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We for the first time report the incorporation of cobalt into a mesoporous TiO electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO, enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO. An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.

The optical and light emission properties of tin and lead halide perovskites are remarkable because of the robust room temperature performance, broad wavelength tunability, high efficiency and good quenching-resistance to defects. These highly desirable attributes promise to transform current light emitting devices, phosphors and lasers. One disadvantage in most of these materials is the sensitivity to moisture. Here we report a new air-stable one-dimensional (1D) hybrid lead-free halide material (DAO)Sn 2 I 6 (DAO: 1,8-octyldiammonium) that is resistant to water for more than 15h.The material exhibits a sharp optical absorption edge at 2.70 eV and a strong broad orange light emission centered at 634 nm, with a full width at half maximum (FWHM) of 142 nm (0.44 eV). The emission has a long photoluminescence (PL) lifetime of 582 ns, while the intensity is constant over a very broad temperature range (145-415 K) with a photoluminescence quantum yield (PLQY) of at least 20.3% at RT. Above 415 K the material undergoes a structural phase transition from monoclinic (C2/c) to orthorhombic (Ibam) accompanied by a red shift in the bandgap and a quench in the photoluminescence emission. Density functional theory calculations support the trend in the optical properties and the 1D electronic nature of the structure, where the calculated carrier effective masses along the inorganic chain are significantly lower than those perpendicular to the chain. Thin films of the compound readily fabricated from solutions exhibit the same optical properties, but with improved PLQY of 36%,

Surface-enhanced Raman spectroscopy (SERS) has recently emerged as an innovative tool for therapeutic-drug monitoring (TDM), making it an ideal candidate for personalized treatment. Herein, we report a layer-by-layer (LbL) approach for the fabrication of a highly reproducible hybrid SERS substrate based on graphene oxide (GO)-supported l-cysteine-functionalized starlike gold nanoparticles (SAuNPs). These designed substrates were utilized for TDM of paclitaxel and cyclophosphamide in blood serum. The SAuNPs’ efficient binding at the edges of GO creates a better SERS hotspot with enhanced Raman sensitivity because of the spacing of ∼2.28 nm between the SAuNPs. In addition, the hierarchically modified substrate with a self-assembled monolayer of zwitterionic amino acid l-cysteines acts like a brush layer to prevent SERS-hotspot blockages and fouling by blood-serum proteins. The antifouling nature of the substrate was determined quantitatively by a bichinchonic acid assay using bovine-serum albumin (BSA) as a protein model on the l-cysteine SAuNPs@GO hybrid substrate (the test) and a cysteamine SAuNPs@GO substrate (the control). The l-cysteine SAuNPs@GO hybrid exhibited 80.57% lower BSA fouling compared with that of the cysteamine SAuNPs@GO substrate. The SERS spectra were acquired within 20 s, with detection limits of 1.5 × 10–8 M for paclitaxel and 5 × 10–9 M for cyclophosphamide in blood serum. Such sensitivities are 4 times and 1 order of magnitude higher than the currently available sophisticated analytical techniques, which involve high costs with each analysis.