RESUMEN
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.
RESUMEN
The wide-bandgap methylammonium lead bromide perovskite is promising for applications in tandem solar cells and light-emitting diodes. Despite its utility, there is a limited understanding of its reproducibility and stability. Herein, the dependence of the properties, performance, and shelf storage of thin films and devices on minute changes to the precursor solution stoichiometry is examined in detail. Although photovoltaic cells based on these solution changes exhibit similar initial performance, shelf storage depends strongly on precursor solution stoichiometry. While all devices exhibit some degree of healing, bromide-deficient films show a remarkable improvement, more than doubling in their photoconversion efficiency. Photoluminescence spectroscopy experiments performed under different atmospheres suggest that this increase is due, in part, to a trap-healing mechanism that occurs upon exposure to the environment. The results highlight the importance of understanding and manipulating defects in lead halide perovskites to produce long-lasting, stable devices.
RESUMEN
Published studies of layered (2D) (100)-oriented hybrid lead-bromide perovskites evidence a correlation between increased inter-octahedral (Pb-Br-Pb) distortions and the appearance of broadband white light emission. However, the impact of distortions within their constituent [PbBr6 ]4- octahedra has yet to be assessed. Herein, we report two new (100)-oriented 2D Pb-Br perovskites, whose structures display unusually high intra-octahedral distortions, whilst retaining minimal inter-octahedral distortions. Using a combination of temperature-dependent, power-dependent and time-resolved photoluminescence spectroscopic measurements, we show that increased intra-octahedral distortion induces exciton localization processes and leads to formation of multiple photoinduced emissive colour centres. Ultimately, this leads to highly Stokes-shifted, ultrabroad white light emission at room temperature.
RESUMEN
One-dimensional (1D) semiconductor nanorods are important for numerous applications ranging from optics and electronics to biology, yet the direct synthesis of high-quality metal halide perovskite nanorods remains a challenge. Here, we develop an intermediate monomer reservoir synthetic strategy to realize the controllable growth of uniform and low-defect CsPbBr3 perovskite nanorods. Intermediates composed of CsPb2Br5 and Cs3In2Br9 are obtained through the substitution of Pb2+ with In3+ cations in the template of CsPbBr3 nanocubes and act as a precursor reservoir to gradually release monomers, ensuring both the slow growth rate and low defects of nanorods. We have used branched tris(diethylamino)phosphine as a ligand, which not only has unequal binding energies with different crystal faces to promote the orientation growth but also provides strong steric hindrance to shield the nanorods in solution. Because of minor amount of defects and an effective ligand passivation, in addition to significantly enhanced stability, the perovskite nanorods show a high photoluminescence quantum yield of up to 90% and exhibit a net mode gain of 980 cm-1, the latter being a record value among all the perovskite materials. An extremely low amplified spontaneous emission threshold of 7.5 µJ cm-2 is obtained under excitation by a nanosecond laser, which is comparable to that obtained using femtosecond lasers in other recent studies.