Stabilization of alpha-CsPbI3 in Ambient Room Temperature Conditions by Incorporating Eu into CsPbI3

Although inorganic perovskite, CsPbI3, shows superior thermal stability over organic-inorganic hybrid perovskites, stabilization of the photoactive black phase (alpha-CsPbI3) of CsPbI3 perovskite at room temperature and in ambient conditions has remained a challenge. Herein, we present a method of stabilizing the alpha-CsPbI3 at lower annealing temperature (85 degrees C) by incorporation of Eu3+ (EuCl3) into CsPbI3, which prevents the black to the yellow phase (delta-CsPbI3) transformation in ambient air (room temperature) for a reasonably long time (>30 days). Photovoltaic performance of this Eu-stabilized alpha-CsPbI3, as assessed in planar heterojunction solar cells (FTO/TiO2/CsPbI3:xEu/spiro-OMeTAD/Au), shows a power conversion efficiency above 6% on backward scan (stabilized power output above 4%) for CsPbI3:xEu cells with 5-6 mol % of Eu, while CsPbI3 without Eu, as expected, shows no photovoltaic property at all. However, as the cell stability was found to be affected by composition of organic hole transport material (HTM) (spiro-OMeTAD) and morphology of CsPbI3 film, it is believed that optimization of cell composition and structure with a more suitable HTM will further improve the cell performance, as well as life.