Revealing the Dynamics of Hybrid Metal Halide Perovskite Formation via Multimodal In Situ Probes

Abstract

The exploration of the synthetic space of halide perovskites hinges on an enormous number of parameters requiring time-consuming experimentation to decouple and optimize. Here, the formation of the prototype material CH 3 NH 3 PbI 3 (MAPbI 3 ) is investigated at different time and length scales using multimodal in situ measurements to monitor the evolution of crystalline phases, morphology, and photoluminescence as a function of the lead precursors. Kinetically fast formation of crystalline precursor phases already during the spin-coat deposition is observed using lead iodide (PbI 2 ) or lead chloride (PbCl 2 ) routes. These precursor phases most likely template final MAPbI 3 film morphology. In particular, the emergence of the "needle-like" structure is shown to appear before film annealing. In situ photoluminescence measurements suggest nanoscale nucleation followed by rapid nuclei densification and growth. Using this multimodal in situ approach, different formation pathways can be identified either via precursor phases in the PbI 2 and PbCl 2 routes or direct perovskite formation from molecular building blocks as observed in the lead acetate (PbAc 2 ) route. Correlation of in situ results with photovoltaic device performance demonstrates the power of in situ multimodal techniques, paves the way to a fast screening of synthetic parameters, and ultimately leads to controlled synthetic procedures that yield high-efficiency devices.

Dynamics of Antisolvent Processed Hybrid Metal Halide Perovskites Studied by In Situ Photoluminescence and Its Influence on Optoelectronic Properties

“…33,34 Co-presence of PbI 2 (diffraction peak ~12.7º) and intermediate orthorhombic phase (MA) 2 (DMF) 2 Pb 3 I 8 was observed when the antisolvent was dripped late, as well as in the film without antisolvent. 19,35 In a previous study we performed in situ diffraction and optical microscope measurements during the synthesis of MAPbI 3 and confirmed the formation of the intermediate (MA) 2 (DMF) 2 Pb 3 I 8 phase together with the needle-like morphology. 35 In addition, enabled by a fully remotely controlled spin coater in the synchrotron hutch, we found that this phase does not require thermal activation but forms already during spin coating and converts into the perovskite phase after about 15s of annealing.…”

“…19,35 In a previous study we performed in situ diffraction and optical microscope measurements during the synthesis of MAPbI 3 and confirmed the formation of the intermediate (MA) 2 (DMF) 2 Pb 3 I 8 phase together with the needle-like morphology. 35 In addition, enabled by a fully remotely controlled spin coater in the synchrotron hutch, we found that this phase does not require thermal activation but forms already during spin coating and converts into the perovskite phase after about 15s of annealing. 35 Thus, if the antisolvent is dripped late (or in the absence of an antisolvent) PbI 2 -MAI-DMF 36 (N,N-dimethylformamide) complex formation happens which templates the final film structure into a non-compact, needlelike morphology.…”

“…35 Thus, if the antisolvent is dripped late (or in the absence of an antisolvent) PbI 2 -MAI-DMF 36 (N,N-dimethylformamide) complex formation happens which templates the final film structure into a non-compact, needlelike morphology. 18,19,35 Upon annealing, the crystallinity significantly improves, as evidenced by the drop in full width at half maximum (FWHM) of the (110) peak (~14.1º) (Supporting Information Figure S2). The smallest FWHM characteristic for larger domain sizes is observed if the antisolvent is dripped late or no antisolvent is applied.…”

Synthetic approaches for thin-film halide double perovskites

“…As an example, in situ synchrotron diffraction measurements can provide valuable insights and unveil precursor transformation kinetics and secondary phase evolution. 164 The independent control of nucleation and growth during processing of ABX 3 perovskites was identified as a major step towards high quality films including fast initial nucleation to promote uniform coverage but omit microstructural defects. 9 In-depth studies are needed to deconvolve these processes and provide a mechanistic understanding of how nucleation can be promoted and controlled.…”

Carrier diffusion coefficient is independent of defects in CH3NH3PbBr3 single crystals: Direct evidence

“…In contrast, a few reports have shown that the CH 3 NH 3 PbI 3 thin films fabricated with the addition of PbCl 2 contained slight amount of chloride residues in perovskite grains, which was believed to be responsible for the longer carrier lifetimes [19][20][21][22]. Although the exact role of chloride ion in the growth of perovskite still remains unclear, it has be suggested that chloride ion improves the crystallinity of perovskites, leading to better photophysical properties [13,14,23]. The optical images of the as-grown CH 3 NH 3 PbBr 3 NWs and NPs synthesized with different PbCl 2 /PbAc 2 molar ratios (M) were shown in Fig.…”