Paifeng Luo,Zhaofan Liu,Wei Xia,Chenchen Yuan,Jigui Cheng,Chenxi Xu,Yingwei Lu
Currently, chlorine (Cl)-incorporated perovskite solar cells (PSCs) have triggered a strong interest due to their excellent crystallinity and charge transport property. Herein, we present a facile MaCl-assisted (Ma = CH3NH3) sequential tubular chemical vapor deposition (STCVD) method to fabricate perovskite films, and report for the first time novel Cl-conducted defect repairment and seed crystal-mediated vapor growth behavior. Further studies indicate that Cl has an ultra-strong reaction capacity and special grain refining ability, and these unique features can effectively heal the inherent ditch defects on PbI2 templates and overcome the blocking issue of incomplete conversion in perovskites. With the aid of Cl, the well-defined MaPbI3−xClx small seed crystals are obtained and then grow up into compact, crack-free, and highly uniform MaPbI3 layers with large grain size up to the microscale. Accordingly, the big open-circuit voltage (Voc) exceeding 1.0 V and high efficiency of 13.76% of our STCVD-processed PSCs measured without aperture mask are successfully achieved in this work. Strikingly, our perovskite device without encapsulation still has an efficiency of 4.15% even after exposure to the ambient conditions for 1152 hour. Overall, we propose a viable strategy to realize the controllable preparation of PSCs, and also disclose the exact role of Cl in film morphology evolution during the gas–solid (G–S) growth process.
Jilin Wang,Shaofei Li,Wenbiao Li,Yuchun Ji,Dongping Lu,Rifeng Xiao,Fei Long
A simple method was developed for the controllable synthesis of novel BN-coated aluminum borate (Al 18 B 4 O 33 ) heterogeneous core-shell nanowires using Al 4 B 2 O 9 nanowhiskers as rigid templates. This method allows the fabrication of Al 18 B 4 O 33 nanowires with BN coatings of different thicknesses. The phases, microstructures, and chemical compositions of the samples were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and other characterization techniques. The heterogeneous core-shell nanowires of BN/Al 18 B 4 O 33 had diameters and tube lengths of 35–60 nm and 400–600 nm, respectively, and the thickness of the BN cladding shell was between 2 and 7 nm. The concentration of B* volatilized on the whisker surface could be controlled by varying the ammonia flow rate, which in turn regulated the thickness of the BN cladding layer . The thickness of the BN cladding changed more significantly when the ammonia flow rate was varied at the Al 4 B 2 O 9 nanowhisker's decomposition temperature. The experimental results show that the BN on the BN/Al 18 B 4 O 33 heterogeneous core-shell structured nanowires conforms to the vapor–solid (VS) growth mechanism.
This paper presents a novel vapor–solid growth approach of stem-like 1D vanadium oxide nanostructures in a core-regenerated fashion on VO2@TiO2 core–shell rods under a very low temperature (400 °C). The composition and microstructure of the as-grown nanostructures were analyzed by HRTEM, EDS and XPS, confirming the vapor–solid mechanism. The confinement effect of the shell was analyzed by varying experimental parameters (coating thickness and heating rate), and the shell was found to play a critical role in generating and accumulating vapor with supersaturated concentration for the nanocrystal nucleation. Additionally, PVP was added as a surface modifier to favor the growth, probably by forming carbonaceous/nitrogen gaseous species as carrier media, as deduced by FTIR analysis. By exploring the impact of different heating rates, we found that the mass transfer process was facilitated only using a relatively high heating rate (>1.33 °C s−1). However, such a growth was still limited only within the early stages (~15 min), because the confined vacuum interface will disappear with the progress of the crystallization of the nanoporous anatase shell. A unique 1D rods to 2D nano-flakes evolution can be achieved by increasing the heating rate from 1.3 °C s−1 to over 8 °C s−1. These findings provide a valuable understanding on the thermodynamics and kinetics during an unique VS based nanocrystal growing process, and also showed a new method to obtain hierarchical heterogeneous nanostructures.
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