Role of solution concentration in formation kinetics of bromide perovskite thin films during spin-coating monitored by optical in situ metrology. Issue 50 (15th November 2022)

• Record Type: Journal Article
• Authors: Rehermann, C.; Schröder, V.; Flatken, M.; Ünlü, F.; Shargaieva, O.; Hoell, A.; Merdasa, A.; Mathies, F.; Mathur, S.; Unger, E. L.
• Is Part Of: RSC advances. Volume 12:Issue 50(2022)
• Page Start: 32765
• Page End: 32774
• Publication Date: 2022-11-15
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d2ra06314j
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : The solution chemistry of the precursor ink defines the formation kinetics of metal halide perovskites. Thus, rationalizing the formation process from solution via the deposition paves the way for high-quality thin films for optoelectronic devices. Abstract : Optoelectronic devices based on metal halide perovskites continue to show a improved performance, and solution-based coating techniques pave the way for large-area applications. However, not all parameters influencing the thin film formation process of metal halide perovskites are identified and entirely rationalised over their full compositional range, thus hampering optimised thin film fabrication. Furthermore, while the perovskite deposition via spin-coating and annealing is an easily accessible technique, more profound insights into the chemical formation process are still lacking. Varying the precursor solution concentration is commonly used to vary the resulting thin film thickness. This study shows that varying the precursor solution concentration also affects the thin film morphology and optoelectronic quality. Hence, we herein investigate the influence of the precursor solution concentration on the formation process of a pure bromide-based triple cation perovskite (Cs0.05 MA0.10 FA0.85 PbBr3 ) by fiber-based optical in situ measurement. During the spin-coating process, in situ UV-vis and PL measurements reveal formation kinetics are strongly dependent on the concentration. Furthermore, we identify delayed nucleation and retarded growth kinetics for more concentrated precursor solutions. In addition, we quantify the shifting chemical equilibrium of colloidal pre-coordination in the precursor solution depending on concentration. Namely, colloids are pre-organised to a higher degree and higher-coordination lead–bromide complexes tend to form in more concentrated precursor solutions. Thus, the modified solution chemistry rationalises retarded perovskite formation kinetics and highlights the precursor concentration as an influential and optimisable parameter for solution-based thin film deposition.