Mechanism of Additive-Assisted Room-Temperature Processing of Metal Halide Perovskite Thin Films

Abstract

Perovskite solar cells have received substantial attention due to their potential for low-cost photovoltaic devices on flexible or rigid substrates. Thiocyanate (SCN)-containing additives, such as MASCN (MA = methylammonium), have been shown to control perovskite film crystallization and film microstructure to achieve effective room-temperature perovskite absorber processing. Nevertheless, the crystallization pathways and mechanisms of perovskite formation involved in MASCN-additiveprocessing are far from clear. Using in situ X-ray diffraction and photoluminescence, we investigate the crystallization pathways of MAPbI 3 and reveal the mechanisms of additive-assisted-perovskite formation, during spin coating and subsequent N 2 -drying. We confirm that MASCN induces large precursor aggregates in solution and, during spin coating, promotes the formation of the perovskite phase with lower nucleation density and overall larger initial nuclei size, that form upon reaching supersaturation in solution, in addition to intermediate solvent-complex phases. Finally, during the subsequent N 2 -drying, MASCN facilitates the dissociation of these precursor aggregates and the solvate phases, leading to further growth of the perovskite crystals. Our results show that the nature of the intermediate phases and their formation/dissociation kinetics determine the nucleation and growth of the perovskite phase, which subsequently impacts the film microstructure. These findings provide mechanistic insights underlying roomtemperature, additive-assisted, perovskite-processing and help guide further development of such facile room-temperature synthesis routes.

Performance-limiting formation dynamics in mixed-halide perovskites

“…For in situ PL measurement, a homebuilt platform consists of a 532-nm laser diode and an Ocean Optics Spectrometer (Flame) coupled with optical fibers, optical filters, and several planoconvex lenses described in our previous reports were used ( 34 , 35 ). The power density of the laser was approximately 100 mW/cm 2 as the intensity reaching the sample could vary as adjusting the setup.…”

Understanding Differences in the Crystallization Kinetics between One‐Step Slot‐Die Coating and Spin Coating of MAPbI3 Using Multimodal In Situ Optical Spectroscopy

“…and photoluminescence (PL) being measured in parallel during processing of halide perovskites from solution, or even combinations of scattering and optical spectroscopy, [29,30] allowed to gain insights into the perovskite formation process.…”

Growth and Degradation Kinetics of Organic–Inorganic Hybrid Perovskite Films Determined by In Situ Grazing‐Incidence X‐Ray Scattering Techniques

“…Reproduced with permission. [ 80 ] Copyright 2021, American Chemical Society. E‐a) In situ GIWAXS data and b) the integrated peak intensities for FASnI 3 during the drying process.…”

“…In the subsequent nitrogen drying process, the MASCN sample showed a faster intermediate phase dissociation and perovskite formation compared to the control sample. [ 80 ] Song et al. used in situ GIWAXS measurements to study the effect of 1,8‐diiodooctane (DIO) additives on the crystallization of perovskite films prepared with slot‐die printing.…”

“…Abdelsamie et al introduced thiocyanate (SCN) into the MAPbI 3 precursor solution and observed its influence on the phase evolution during the spinning coating and nitrogen drying process. [80] In order to depict the evolution details of the concerned phases, the extracted characteristics from in situ GIWAXS data was plotted and shown in Figure 4D. Apart from the formation of solvated intermediated phases, the MASCN additives were found to induce the formation of an unidentified intermediate phase and the early crystallization of perovskite phase during spin coating.…”