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

The antisolvent dripping time during spin-coating of CH₃NH₃PbI₃ (MAPbI₃) strongly impacts film morphology as well as possible formation of the intermediate precursor phase andconsequentlydevice performance. Here, we use in situ photoluminescence (PL) to directly monitor the fast-occurring changes during MAPbI₃ synthesis. These measurements reveal how the ideal timing of the antisolvent leads to homogeneous nucleation and pinhole-free films. In addition, these films show significantly reduced nonradiative recombination with 1.5 orders of magnitude difference in absolute PL quantum yield compared to films where no antisolvent is applied. Low-temperature PL measurements confirm that antisolvent treatment reduces the number of trap states presumably in the bulk material. However, if the antisolvent is dripped late, heterogeneous nucleation via the orthorhombic (MA)₂(DMF)₂Pb₃I₈ intermediate phase leads to a needle-like morphology that can be correlated to a red-shifted in situ PL signature. We find that the ideal dripping window is very narrow when using dimethyl­formamide as the solvent, confirmed by device performance metrics. Finally, the use of in situ PL is discussed to gain information about nucleation and growth and ultimately increase reproducibility.