Blade-Coated Hybrid Perovskite Solar Cells with Efficiency > 17%: An In Situ Investigation

Blade-coating has recently emerged as a scalable fabrication method for hybrid perovskite solar cells, but it currently underperforms spin-coating, yielding a power conversion efficiency (PCE) of -15% for CH3NH3 PbI3 (MAPbI(3)). We investigate the solidification of MAPbI(3) films in situ during spin/blade-coating using optical and X-ray scattering methods. We find that the coating method and conditions profoundly influence the crystallization process, which proceeds through intermediate crystalline solvates. The polymorphism and composition of the solvates are mediated by the solvent removal rate dictated by the process temperature in blade-coating. Low to intermediate temperatures (25-80 degrees C) yield solvates with differing compositions and yield poor PCEs (similar to 5-8%) and a large spread (+/- 2.5%). The intermediate solvates are not observed at elevated temperatures (>100 degrees C), pointing to direct crystallization of the perovskite from the sol-gel ink. These conditions yield large and compact spherulitic domains of perovskite and improve the PCE to similar to 13-15% with a narrower spread (< +/- 0.5%), while coating at 150 degrees C yields 17.5% solar cells by inducing in situ decomposition of a small amount of MAPbI(3) into PbI2. The insights into the crystallization pathway highlight the current challenges and future opportunities associated with scaling up hybrid perovskite solar cell manufacturing.