Unipolar self-doping behavior in perovskite CH3NH3PbBr3

Abstract

Recent theoretical and experimental reports have shown that the perovskite CH3NH3PbI3 exhibits unique ambipolar self-doping properties. Here, we show by density-functional theory calculation that its sister perovskite, CH3NH3PbBr3, exhibits a unipolar self-doping behavior—CH3NH3PbBr3 presents only good p-type conductivity under thermal equilibrium growth conditions. We further show that despite a large bandgap of 2.2 eV, all dominant defects in CH3NH3PbBr3 create shallow levels, which partially explains the ultra-high open-circuit voltages achieved by CH3NH3PbBr3-based thin-film solar cells. Our results suggest that the perovskite CH3NH3PbBr3 can be both an excellent solar cell absorber and a promising low-cost hole-transport material for lead halide perovskite solar cells.

Fabrication and Characterization of CH3NH3PbI3−x−yBrxCly Perovskite Solar Cells

“…The energy levels of the HOMO, band gap and the carrier mobility of electron transporting layer could be controlled by combination of hydrogen doping of I, Cl and Br with molar ratio in the perovskite crystal structure [18][19][20][21][22][23][24][25][26][27]. Incorporation of Cl and Br as dopants into the perovskite crystalline structure improved the crystal growth and size, the carrier transporting properties and the photovoltaic performance of Voc, Jsc and PCE.…”

“…Control of halogen doping with molar ratio between I, Cl and Br in perovskite crystal structure will provide the best condition for the photovoltaic performance, the crystal structure, carrier mobility and electronic electronic structure with band gaps between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and the optical properties with a wide range of absorption. The insertion of both Cl and Br into the perovskite structure promoted the carriergeneration, and expanded carrier diffusion and lifetime, along with reducing the charge recombination in the active layers for improving the photovoltaic performance [14][15][16][17][18][19][20]. A detailed description of the photovoltaic properties, structural analysis, and theoretical investigation using Xray diffraction pattern (XRD), X-ray photoelectron spectroscopy, scanning electronic microscopy (SEM) and density-functional theory calculation of halogen-doped perovskite layer of CH3NH3PbI3−xClx, CH3NH3PbBr3−xClx, CH3NH3SnX3 (X = Cl, Br, I), [HC(NH2)2]0.83Cs0.17Pb(I0.6Br0.4)3], antimony-doped CH3NH3PbI3, CH3NH3Pb1−xGexI3, CH3NH3Pb1−xTlxI3 and CH3NH3Pb1−xInxI3 on TiO2 layers has been reported [18][19][20][21][22][23][24][25][26][27][28][29].…”

Electronic structure and stability of the CH3NH3PbBr3 (001) surface

“…In addition, the organo-lead halide perovskites show long electron-hole diffusion lengths (exceeding 1 micrometer) and high mobilities for both electron and hole charge carriers, resulting in ambipolar charge transport [18][19][20][21][22][23]. The band gap (in the region of 2 eV) and shallow defect levels, even at the surface, also contribute to their remarkable photovoltaic performance [24][25][26].…”

Role of bromine doping on the photovoltaic properties and microstructures of CH3NH3PbI3 perovskite solar cells

“…The Voc of the perovskite solar cells would be related to the energy gap between the valence band of CH3NH3PbI3 and, conduction band of TiO2. The energy levels of the highest occupied molecular orbital (HOMO), band gap and the carrier mobility of hole-transport layer can be controlled by hydrogen doping in the perovskite crystal structure [18][19][20]. Incorporation of chloride as dopant into the perovskite crystalline structure slightly improved the photovoltaic performance of Voc, Jsc and η.…”

“…Control of molar ratio between iodine, chloride and bromide in perovskite crystal structure will provide a best condition of the photovoltaic performance, the crystal structure, carrier mobility and electronic structure and band gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and the optical absorption. The insertion of both chloride and bromide in the perovskite structure provided to promote carrier-generation and expanding carrier diffusion with reducing the charge recombination in the light absorber film, yielding improvement of the photovoltaic performance [14][15][16][17][18][19][20] A detail of structural analysis and theoretical study regarding X-ray diffraction pattern, X-ray photoelectron spectroscopy, scanning electronic microscopy (SEM), field emission scanning electron microscope and density-functional theory calculation of CH3NH3PbBr3−xClx and CH3NH3SnX3 (X = Cl, Br, I) perovskite structure has been reported [18][19][20][21]. The purpose of this study is to fabricate inorganic-organic hybrid solar cells using CH3NH3PbI3 perovskite compounds doped with bromine materials with variable mole ratio.…”