Low dimensional (LD) perovskite materials generally exhibit superior chemical stability against ambient moisture and thermal stress than that of 3D perovskites. Recently, LD perovskite has been used as a passivation layer on the surface of 3D perovskite grains. Although various LD perovskites have been developed focusing on their hydrophobicity, the impact of crystal structure of LD perovskite on the photovoltaic performance of perovskite solar cell (PSC) is still uncertain. In this work, the effects of the structural characteristics of LD perovskites on the crystal formation of formamidinium lead triiodide (α‐FAPbI3) and on the optoelectrical properties of PSCs are elucidated. The phase‐transformation kinetics of FAPbI3 mixed with LD perovskites is studied using the Johnson–Mehl–Avrami–Kolmogorov model. It is found that the arrangement of PbI6 octahedra in the LD perovskite changes the rate of α‐FAPbI3 formation. Facilitated nucleation of α‐FAPbI3 at the LD/FAPbI3 interface results in minimal structural disorder and prolonged charge‐carrier lifetimes. As a result, the PSC with the optimized LD perovskite structure exhibits a power conversion efficiency of 21.25% from a reverse current–voltage scan, and stabilized efficiency of 19.95% with excellent ambient stability without being encapsulated.
Organometal halide perovskites (OHPs) exhibit superior charge transport characteristics and ultralow thermal conductivities. However, thermoelectric (TE) applications of OHPs have been limited because of difficulties in controlling their carrier concentration, which is a key to optimizing their TE properties. Here, facile control of the carrier concentration in Sn‐based OHPs is achieved by developing 2D crystal structures. The 2D OHP crystals are laterally oriented using a mixed solvent, and the morphology and crystal structure of the coexisting 2D/3D hybrid structures are systematically controlled via doping with methylammonium chloride. The effective number neff of inorganic octahedron layers in the 2D OHPs shows a strong positive correlation with the carrier concentration. Moreover, the 2D structure induces the quantum confinement effect, which enhances both the Seebeck coefficient and the electrical conductivity. A 2D OHP shows a high power factor of 111 µW m−1 K−2, which is an order of magnitude greater than the power factor of its 3D counterpart.
Mixed-halide perovskites, CH 3 NH 3 PbI 3−x Cl x , can be used to fabricate highly efficient perovskite solar cells; the presence of chlorine ions affects the perovskite morphology and enhances optoelectronic properties. However, the reported device performances of mixed-halide perovskites are comparable to those of triiodide perovskites, CH 3 NH 3 PbI 3 . Thus, the benefits of the presence of Cl − ions in mixed-halide perovskites are uncertain. To clarify the effects of Cl − on the optoelectronic properties of perovskite devices, a suitable device structure is required. In this study, lateral-structured perovskite devices are fabricated and their electrical properties are investigated. A clear contrast is found between the optoelectronic properties of the mixed-halide and triiodide perovskite; a suitable platform is also constructed for the spectroscopic analysis. Scanning photocurrent spectroscopy is used to visualize the charge carrier diffusion in the perovskite films and it is found that the charge carrier diffusion length of the mixed-halide perovskite is longer. It is also demonstrated by using conducting atomic force microscopy that the charge carrier pathways in the mixed-halide perovskite are more efficient, which means that it has longer charge carrier recombination life-times and higher photocurrents. This lateral-structured device has an architecture that makes it suitable for the observation of charge carrier diffusion and spectroscopic analysis.
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