Functional Group Engineering Stabilizing Precursor Solution and Passivating Defects for Operationally Stable and Highly Reproducible Inverted Perovskite Solar Cells

The instability of perovskite precursor solution induced by deprotonation of organic cations and oxidation of iodide ions substantially deteriorates the reproducibility and reliability of the photovoltaic performance of perovskite solar cells (PSCs). The above decomposition reactions can be conquered via the synergistic engineering of organic functional groups. However, how spatial conformation and type of weak acid functional groups impact the stability of perovskite precursor solution remains to be investigated. Herein, it is uncovered that the position of functional groups on the benzene and the type of weak acid functional groups remarkably influence the acid dissociation constant (pK_a) and thus the stability of perovskite inks. The pK_a plays a decisive role in suppressing the deprotonation of organic cations and following the amine-cation addition-elimination reaction. The 4-hydrazinobenzenesulfonic acid (4-HBSA) with the lowest pK_a is optimal in stabilizing perovskite inks and mitigating nonradiative recombination through defect passivation. This breakthrough enables the inverted PSCs to deliver a power conversion efficiency (PCE) of 26.79% (certified 26.36%, the highest PCE value for PSCs prepared in ambient conditions) using vacuum flash evaporation technology. The modulated PSC could maintain 92% of its initial efficiency after 2000 h of continuous maximum power point tracking.