ABSTRACT
Halide composition engineering has been demonstrated as an effective strategy for optical and electronic properties modulation in 3D perovskites. While the impact of halide mixing on the structural and charge transport properties of 3D perovskitoids remains largely unexplored. Herein, it is demonstrated that bromine (Br) mixing in 3D (NMPDA)Pb2 I6 (NMPDA = N-methyl-1,3-propane diammonium) perovskitoid yields stabilized (NMPDA)Pb2 I4 Br2 with specific ordered halide sites, where Br ions locate at the edge-sharing sites. The halide ordered structure enables stronger H-bonds, shorter interlayer distance, and lower octahedra distortion in (NMPDA)Pb2 I4 Br2 with respect to the pristine (NMPDA)Pb2 I6 . These attributes further result in high ion migration activation energy, low defect states density, and enhanced carrier mobility-lifetime product (µτ), as underpinned by the electrical properties investigation and DFT calculations. Remarkably, the parallel configured photodetector based on (NMPDA)Pb2 I4 Br2 single crystal delivers a high on/off current ratio of 3.92 × 103 , a satisfying photoresponsivity and detectivity of 0.28 A W-1 and 3.05 × 1012 Jones under 10.94 µW cm-2 irradiation, superior to that of (NMPDA)Pb2 I6 and the reported 3D perovskitoids. This work sheds novel insight on exploring 3D mixed halide perovskitoids toward advanced and stable optoelectronic devices.
ABSTRACT
Two-dimensional (2D) Dion-Jacobson (DJ) perovskites are drawing significant attention in optoelectronic fields because of their enhanced out-of-plane electron coupling and improved structure stability. However, the structural effects of organic cations on the in-plane charge transport properties of 2D DJ lead bromide perovskites have remained less explored. Herein, we adopt asymmetric 3-(dimethylamino)-1-propylammonium (DMPD) and symmetric butane-1,4-diammonium (BDA) to systematically investigate the influence of organic cations on the structural, optical, and in-plane charge transport properties of 2D lead bromide perovskites. The large penetration depth of DMPD2+ induces a decreased perovskite layer distortion and a lower bandgap in DMPDPbBr4, compared with that of BDAPbBr4. Moreover, DMPDPbBr4 is shown to possess a low exciton binding energy, a low defect density, and a low ion migration activation energy, thereby yielding a more efficient in-plane charge collection efficiency than BDAPbBr4. Density functional theory calculations suggest that the improved in-plane charge transport can be traced to the enlarged antibonding coupling between Pb-6s and Br-4p orbitals that enables a high band dispersion and a low carrier effective mass in the in-plane direction of DMPDPbBr4. Finally, the planar Ag/DMPDPbBr4/Ag photodetector delivers a satisfying detectivity of 1.73 × 1012 Jones under an incident power intensity of 0.16 mW cm-2 and a high on/off ratio of 5.3 × 103. The above findings offer novel insight for the design of 2D DJ lead bromide perovskites for optoelectronic devices.
ABSTRACT
A large area surface discharge was realized in air/argon gas mixture by designing a discharge device with water electrodes. By using optical emission spectrum, the variations of the molecular vibrational temperature, the mean energy of electron, and the electronic excitation temperature as a function of the gas pressure were studied. The nitrogen molecular vibrational temperature was calculated according to the emission line of the second positive band system of the nitrogen molecule (C3 pi(u) --> B 3 pi(g)). The electronic excitation temperature was obtained by using the intensity ratio of Ar I 763.51 nm (2P(6) --> 1S(5)) to Ar I 772.42 nm (2P(2) --> 1S(3)). The changes in the mean energy of electron were studied by the relative intensity ratio of the nitrogen molecular ion 391.4 nm to nitrogen 337.1 nm. It was found that the intensity of emission spectral line increases with the increase in the gas pressure, meanwhile, the outline and the ratios of different spectral lines intensity also change. The molecular vibrational temperature, the mean energy of electron, and the electronic excitation temperature decrease as the gas pressure increases from 0.75 x 10(5) Pa to 1 x 10(5) Pa.
ABSTRACT
Octagon structure consisting of the spots and lines was firstly observed in discharge in argon and air mixture by using a dielectric barrier discharge device with water electrodes. Plasma temperatures of the spots and lines in octagon structure at different gas pressure were studied by using optical emission spectra. The emission spectra of the N2 second positive band (C3IIu-->B3IIg)were measured, and the molecule vibrational temperatures of the spots and lines were calculated by the emission intensities. Based on the relative intensity of the line at 391.4 nm and the N2 line at 394.1 nm, the average electron energy of the spots and lines were investigated. The spectral lines of Ar I 763.26 nm ((2)P6-1Ss) and 772.13 nm ((2)P2-->1S3) were chosen to estimate electron excitation temperature of the spots and lines by the relative intensity ratio method. The molecule vibrational temperature, average electron energy, and electron excitation temperature of the lines are higher than those of the spots at the same pressure. The molecule vibrational temperature, average electron energy, and electron excitation temperature of the spots and lines decrease with pressure increasing from 40 to 60 kPa.
ABSTRACT
The diffuse discharge plasma in air was observed in a dielectric barrier discharge with two semispherical water electrodes. The variations of vibration temperature, rotation temperature, and average electron energy as the function of the applied voltage were studied by emission spectroscopy. The vibration temperature and the rotation temperature were calculated through the second positive band system (C3Pi(u)-->B3Pi(g)) of N2+ and the first negative band system (B2 Sigma(u+)-->Chi2Sigma(g+)) of N(2+) respectively. The average electron energy was studied by intensity ratio of 391.4 and 337.1 nm. It was found that the rotation temperature increases with the applied voltage increasing, while the vibration temperature and the electron energy decrease.
ABSTRACT
The emission spectrum line shift and vibrational temperature of the bright dot and dark dot discharges, which are observed in the argon and air dielectric barrier discharge at high temperature for the first time were measured and compared. The line shift of the spectral line of the Ar I (2P2-->1S5) is measured and the vibrational temperature was calculated using by the emission spectral lines of the N2 second positive band system (C3Pi(u)-->B3Pi(g)). The results show that the spectrum line shift of the bright dot discharge channel is larger than that of the dark dot channel, which indicates that the former has higher electron density compared to the latter, and the vibrational temperature of the dark dot discharge channel is higher than that of the bright dot discharge channel.
ABSTRACT
The white-eye pattern, whose cell is composed of a bright dot surrounded by a closed hexagon, was observed in air/ argon dielectric barrier discharge. It was found that the center dot, the vertex of hexagon and the center of hexagon side in a cell have different brightness. By using optical emission spectra, the vibrational temperature in the center dot, the vertex of hexagon and the center of hexagon side was measured, respectively. The variations in the vibrational temperature at these three places as a function of the content of argon in gas mixture were also studied. The vibrational temperature was calculated by emission spectral lines of the N2 second positive band system (C3IIu --> B3IIg). The experimental results show that the vibrational temperature of the center dot, the vertex of hexagon and the center of hexagon side is in the ascending order and decreases with the increase in the content of argon in gas mixture.
