Ionic Bilateral Passivator Carboxyethylisothiuronium Chloride for CsPbI3-xBrx Perovskite Solar Cells with PCE 20.9% and Superior Stability

Although the power conversion efficiency (PCE) of all-inorganic perovskite solar cells (PSCs) have achieved great progress in recent years, poor stability is still the critical issue blocking their further development. Hence, we introduce an ionic Lewis base additive carboxyethylisothiuronium chloride (ATP) to amplify the photoelectric property and environmental stability for CsPbI3-xBrx (x = 0.15) PSCs. The Cl- ionized from ATP could apparently optimize the crystallization dynamic process and upgrade the film quality. In addition, isothiourea group and carboxyl group in ATP could effectively fill the vacancies of Cs+ and coordinate with Pb related defects by establishing bilateral synergistic passivation mechanism. Further more, the generation of 2D/3D heterojunctions perovskite structure, the formation of hydrophobic protective layer and release of film stress by ATP are propitious to ameliorating the stability of the device. At last, the 0.02 mol%-ATP optimized device displays the champion efficiency of 20.91%, bringing out one of the highest efficiencies of CsPbI3-xBrx PSCs at present. What's more, the optimized device still maintains 96.1% of the initial PCE in ambient atmosphere without encapsulation after 1000 h, revealing the lowest efficiency attenuation and the best environmental stability so far.