The most notable recent advances in photovoltaic materials have been made using lead halide compounds with perovskite crystal structure. They have conversion efficiencies of greater than 25%, approaching the record efficiencies of well-established single-crystal silicon photovoltaics. In addition, perovskites can be fabricated using low-cost, solution-based processes such as spin coating, offering great potential for clean, inexpensive electricity.
To push performance and increase the stability of these materials, researchers seek to exploit their formulation chemistry to deliberately tailor desirable film properties. To this end, they performed x-ray diffraction experiments at the Advanced Light Source (ALS), where a newly developed spin-coating platform in Beamline 12.3.2 allowed them to probe the perovskite structure during the spin-coating process. Combined with laboratory-based in situ imaging and photoluminescence measurements, the work helped to unravel the formation mechanisms in the very early stages of synthesis.
The results showed that the lead precursor influences the crystallization pathway and can induce formation of an undesirable “needle-like” morphology via a solvent containing crystalline precursor phase. This precursor phase forms fast and does not require thermal activation; the corresponding device performance was found to be poor. In addition, correlating diffraction and photoluminescence data allowed the researchers to understand nucleation, densification, grain growth, and—upon excessive annealing—film decomposition. In a follow-up study, the researchers used this information to explain the importance of antisolvent dripping time to avoid formation of the undesirable precursor phase and thus to optimize PV performance.
This study demonstrates the power of multimodal in situ monitoring and paves the way to developing design rules for more efficient and stable halide perovskite materials.
T.‐B. Song, Z. Yuan, M. Mori, F. Motiwala, G. Segev, E. Masquelier, C.V. Stan, J.L. Slack, N. Tamura, C.M. Sutter‐Fella, “Revealing the Dynamics of Hybrid Metal Halide Perovskite Formation via Multimodal In Situ Probes,” Adv. Funct. Mater., doi: 10.1002/adfm.201908337 (2019).