The Lewis acid–base adduct approach has been widely used to form high‐crystalline perovskite films, but the complicated crystallization pathway and underlying film formation mechanism are still ambiguous. Here, the detailed crystallization process of perovskites manipulated by Lewis base additives has been revealed by in situ X‐ray scattering measurements. Through monitoring the film formation process, two distinct crystal growth stages have been definitely recognized: i) an intermediate phase‐dominated stage; and ii) a phase transformation stage from intermediates to crystalline perovskite phase. Incorporating Lewis base additives significantly prolongs the duration of stage 1 and induces a postponed phase transformation pathway, which could be responsible for retardant crystallization kinetics. Based on a series of experimental results and theoretical calculations, it is indicated that the manipulation of perovskite crystallization pathway is a result of the modulated molecular interactions between Lewis base additives and solution precursors. Owing to the retardant crystallization kinetics, enhanced‐quality perovskite films with reduced defect density and improved optoelectronic properties, as well as optimized photovoltaic performance have been demonstrated. This work provides in‐depth understanding with respect to perovskite crystallization pathway modulated by Lewis base additives and perceptive guidelines for precise regulation of crystallization kinetics of perovskite film toward high performance.
Metal halide perovskite materials, benefiting from a combination of outstanding optoelectronic properties and low‐cost solution‐preparation processes, show tremendous potential for optoelectronics and photovoltaics. However, the nanoscale inhomogeneities of the electronic properties of perovskite materials cause a number of difficulties, such as recombination, stability, and hysteresis, all of which seriously restrict device performance. Scanning probe microscopy, as a high‐resolution imaging technique, has been widely used to connect local properties and micro‐area morphologies to overall device performance. Conductive atomic force microscopy (C‐AFM) can realize a real‐space visualization of topography coupled with optoelectronic properties on a microscopic scale and thereby is uniquely suited to probe the local effects of perovskite materials and devices. The fundamental principles, alternative operation modes, and development of C‐AFM are comprehensively reviewed, and applications in perovskite solar cells (PSCs) for electronic transport behavior, ion migration and hysteresis, ferroelectric polarization, and facet orientation investigation are discussed. A comprehensive understanding and summary of up‐to‐date applications in PSCs is beneficial to further fully exploit the potential of such an emerging technique, so as to provide a novel and effective approach for perovskite materials analysis.
the plane wave cutoff energy was 400 eV. The crystal structure was fully relaxed until all atomic forces were less than 0.05 eV Å −1 and at each selfconsistent field iteration the convergence criterion of the total energy was 0.2 meV. The climbing-image nudged elastic band method (CI-NEB) was used to find the minimum energy path around Rb to confirm the diffusion energy barrier of iodine. [58]
Fundamental understanding of ion
migration inside perovskites is
of vital importance for commercial advancements of photovoltaics.
However, the mechanism for external ions incorporation and its effect
on ion migration remains elusive. Herein, taking K+ and
Cs+ co-incorporated mixed halide perovskites as a model,
the impact of external ions on ion migration behavior has been interpreted
via multiple dimensional characterization aspects. The space-effect
on phase segregation inhibition has been revealed by the photoluminescence
evolution and in situ dynamic cathodoluminescence
behaviors. The plane-effect on current suppression along grain boundary
has been evidenced via visualized surface current mapping, local current
hysteresis, and time-resolved current decay. And the point-effect
on activation energy incremental for individual ions has been also
probed by cryogenic electronic quantification. All these results sufficiently
demonstrate the passivated ion migration results in the eventually
improved phase stability of perovskite, of which the origin lies in
various ion migration energy barriers.
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