A Coadditive Strategy for Blocking Ionic Mobility in Methylammonium‐Free Perovskite Solar Cells and High‐Stability Achievement
Résumé
The present work describes the synthesis of methylammonium-free and bromide-free CsxFA1-xPbI3 (FA for formamidinium) perovskite photovoltaic layers with intrinsic outstanding properties in terms of crystallinity, defect waiving/passivation and ionic mobility blocking by using a co-additives approach. It consists in mixing two chloride additives in the perovskite precursor solution: potassium chloride and ammonium chloride. KCl favors the PbI2 precursor solubilization and results in purer perovskite phase. NH4Cl allows the control of the crystallization growth speed, leads to the formation of large crystal grains and well-crystallized layers. By the glow-discharge optical emission spectroscopy (GD-OES) technique, we have been able to directly visualize that potassium incorporated in the whole film blocks the iodide mobility by defect passivation. We have also clearly correlated the reduction (or suppression) of iodide mobility and the reduction (or suppression) of the J-V curve hysteresis. We have found that blocking the ionic mobility is insufficient to fully stabilize the halide perovskite material which also requires the crystallization monitoring performed in parallel by the second additive. It resulted in Cs0.1FA0.9PbI3 cells with a stabilized PCE at 20.02% and with superior stability.
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