Title | Controlling the formation process of Methylammonium-Free Halide Perovskite films for a homogeneous incorporation of alkali metal cations beneficial to solar cell performances
Date | January 9, 2023
Abstract |Incorporating multiple cations of the IA alkali metal column of the periodic table (K+/Rb+/Cs+) to prepare perovskite films is promising for boosting the photovoltaic properties. However, contrary to K+, both Cs+ and Rb+ suffer from non-uniformity at the origin of performance and stability losses. In our work, Ammonium chloride (NH4Cl) additive is shown to address this concern. We have found the conditions for the preparation of perovskite layers with an homogeneous distribution of multi-alkali metal cations (m-AMC), especially Rb+. The mechanism of ammonium chloride action in m-AMCs perovskites, refined at each preparation process step, has been unveiled. Through a serious analysis, we found that ammonium chloride mainly leads to the formation of intermediates which can increase the solubility of PbI2 and then favor the phase formation and transformation. Secondly, we explored the movement of m-AMCs in the perovskite layer during the film formation process by using the GD-OES (Glow Discharge-Optical Emission Spectroscopy) technique and presented the intuitive evidence of phase segregation caused by potassium. We also confirmed that the atomic ratios change with the depth and that the targeted growth direction of the film is lateral growth. Moreover, we combined this additive with GD-OES detection technology. We found how the additive influence the distribution of m-AMCs film formation. Finally, 22.53% PCE (stabilized at 22.04%) was achieved. m-AMCs, it is multi-alkali metal cations. For GD-OES, it is glow discharge optical emission spectroscopy (GD-OES) technique.
