ABSTRACT
Photochemical and photocatalytic activity of adsorbates on surfaces is strongly dependent on the nature of a given substrate and its resonant absorption of the (visible) light excitation. An observation is reported here of the visible light photochemical response of formamidinium lead bromide (FAPbBr3) halide perovskite and carbon nitride (CN) thin-film materials (deposited on a SiO2/Si(100) substrate), both of which are known for their photovoltaic and photocatalytic properties. The goal of this study was to investigate the role of the substrate in the photochemical reactivity of an identical probe molecule, ethyl chloride (EC), when excited by pulsed 532 nm laser under ultrahigh vacuum (UHV) conditions. Postirradiation temperature-programmed desorption (TPD) measurements have indicated that the C-Cl bond dissociates following the visible light excitation to form surface-bound fragments that react upon surface heating to form primarily ethane and butane. Temperature-dependent photoluminescence (PL) spectra of the FAPbBr3 films were recorded and decay lifetimes were measured, revealing a correlation between length of PL decay and the photoreactivity yield. We conclude that the FAPbBr3 material with its absorption spectrum in resonance with visible light excitation (532 nm) and longer PL lifetime leads to three times faster (larger cross-section) photoproduct formation compared with that on the CN substrate. These results contrast the behavior under ambient conditions where the CN materials are photochemically superior due, primarily, to their stability within humid environments.
ABSTRACT
Organic-inorganic perovskite structured compounds have recently emerged as attractive materials in the fields of photovoltaic due to their exciting optical properties and easy syntheses, as well as exceptional structural and optical tunability. This work presents a Dion-Jacobson two-dimensional (2D) perovskite using diammonium as the barrier molecule. We show that the diammonium barrier molecule is responsible for the perovskite layers' orientation supported by Hall Effect measurements, which results in a high efficiency solar cell for 2D perovskite without the need for additives or any additional treatment. The 2D perovskite cells achieved an efficiency of 15.6%, which was one of the highest reported for low-dimensional perovskite. Charge extraction, voltage decay, and charge collection efficiency measurements show the beneficial alignment of the 2D perovskites related to the selective contacts. Stability characterization shows that the stability for the 2D perovskite was enhanced compared with their 3D counterparts.
ABSTRACT
In this work, we performed a detailed study of the phase transformations and structural unit cell parameters of CsPbBr3 nanoparticles (NPs) and thin films. In situ X-ray diffraction patterns were acquired as a function of temperature, where the positions and widths of the diffraction peaks were systematically tracked upon heating and cooling down to room temperature (RT). Scanning electron microscopy provides physical insight on the CsPbBr3 thin films upon annealing and transmission electron microscopy gives physical and crystallographic information for the CsPbBr3 NPs using electron diffraction. The secondary phase(s) CsPb2Br5 (and CsPb4Br6) are clearly observed in the XRD patterns of both nanoparticles and thin films upon heating to 500 K, whilst from 500 K to 595 K, these phases remain in small amounts and are kept like this upon cooling down to RT. However, in the case of thin films, the CsPb2Br5 secondary phase disappears completely above 580 K and pure cubic CsPbBr3 is observed up to 623 K. The CsPbBr3 phase is then kept upon cooling down to RT, achieving pure CsPbBr3 phase. This study provides detailed understanding of the phase behavior vs. temperature of CsPbBr3 NPs and thin films, which opens the way to pure CsPbBr3 phase, an interesting material for optoelectronic applications.
ABSTRACT
Inorganic and organic lead halide perovskite materials attract great interest in the scientific community because of their potential for low-cost, high efficiency solar cells. In this report we add a new property of these materials, namely their photochemical activity in the visible light range. Both inorganic (CsPbBr3) and organic (CH3NH3PbBr3-MAPbBr3) perovskite thin films were demonstrated to promote photo-dissociation of adsorbed ethyl chloride (EC), employing 532 nm pulsed laser irradiation under ultra-high vacuum (UHV) conditions. From the post-irradiation temperature programmed desorption (TPD) analysis, the yield of photoproduct formation was found to be up to two orders of magnitude higher than for UV light-excited EC molecules on metallic and oxide surfaces. Photo-reactivity on top of the CsPbBr3 surface is almost an order of magnitude more efficient than on the CH3NH3PbBr3 surface, apparently due to the lower density of defect and surface states. A direct correlation was found between electron-induced luminescence and photoluminescence intensities and the photoreactivity cross-sections. We conclude that both the intense luminescence and the well-known photovoltaic properties associated with these halide perovskite materials are consistent with the efficiency of photo-reactivity in the visible range, reported here for the first time.
ABSTRACT
Three-dimensional (3 D) perovskite has attracted a lot of attention owing to its success in photovoltaic (PV) solar cells. However, one of its major crucial issues lies in its stability, which has limited its commercialization. An important property of organic-inorganic perovskite is the possibility of forming a layered material by using long organic cations that do not fit into the octahedral cage. These long organic cations act as a "barrier" that "caps" 3 D perovskite to form the layered material. Controlling the number of perovskite layers could provide a confined structure with chemical and physical properties that are different from those of 3 D perovskite. This opens up a whole new batch of interesting materials with huge potential for optoelectronic applications. This Minireview presents the synthesis, properties, and structural orientation of low-dimensional perovskite. It also discusses the progress of low-dimensional perovskite in PV solar cells, which, to date, have performance comparable to that of 3 D perovskite but with enhanced stability. Finally, the use of low-dimensional perovskite in light-emitting diodes (LEDs) and photodetectors is discussed. The low-dimensional perovskites are promising candidates for LED devices, mainly because of their high radiative recombination as a result of the confined low-dimensional quantum well.
