Effect of Co‐Solvents on the Crystallization and Phase Distribution of Mixed‐Dimensional Perovskites

• Published in: Advanced energy materials 2021-11, Vol.11 (42), p.n/a
• Main Authors: Caiazzo, Alessandro, Datta, Kunal, Jiang, Junke, Gélvez‐Rueda, María C., Li, Junyu, Ollearo, Riccardo, Vicent‐Luna, José Manuel, Tao, Shuxia, Grozema, Ferdinand C., Wienk, Martijn M., Janssen, René A. J.
• Format: Article
• Language: English
• Subjects: Crystal structure; Crystallization; Density functional theory; Dimethyl sulfoxide; Dimethylformamide; Energy conversion efficiency; film formation; Infrared spectroscopy; Optoelectronics; Perovskites; Phase distribution; Photoluminescence; Photovoltaic cells; Ruddlesden‐Popper perovskites; Solar cells; solvent engineering; Solvents; Spectrum analysis; Tuning
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202102144

Solution‐processed quasi‐2D perovskites are promising for stable and efficient solar cells because of their superior environmental stability compared to 3D perovskites and tunable optoelectronic properties. Changing the number of inorganic layers (n) sandwiched between the organic spacers allows for tuning of the bandgap. However, narrowing the phase distribution around a specific n‐value is a challenge. In‐situ UV–vis–NIR absorption spectroscopy is used to time‐resolve the crystallization dynamics of quasi‐2D butylammonium‐based (BA) perovskites with  = 4, processed from N,N‐dimethylformamide (DMF) in the presence of different co‐solvents. By combining with photoluminescence, transient absorption, and grazing‐incidence wide‐angle X‐ray scattering, the crystallization is correlated to the distribution of phases with different n‐values. Infrared spectroscopy and density functional theory reveal that the phase distribution correlates with perovskite precursor—co‐solvent interaction energies and that stronger interactions shift the phase distribution towards smaller n‐values. Careful tuning of the solvent/co‐solvent ratio provides a more homogeneous phase distribution, with highly oriented perovskite crystals and suppressed formation of n = 1–2 phases, providing a power conversion efficiency for BA2MA3Pb4I13 solar cells that increases from 3.5% when processed from DMF to over 11% and 10% when processed from DMF/dimethyl sulfoxide and DMF/N‐methyl‐2‐pyrrolidone mixtures, respectively. The interaction energies of solvents and co‐solvents with perovskite precursors control the crystallization dynamics of mixed dimensional perovskites. Solvent engineering thus enables the manipulation of the phase distribution towards favorably oriented 2D phases with a narrow distribution of the number of inorganic layers in the 2D perovskite towards materials that provide solar cells with efficiency exceeding 11%.