Uncovering Aging Chemistry of Perovskite Precursor Solutions and Anti‐aging Mechanism of Additives

The aging of precursor solutions is the major stumbling block for the commercialization of perovskite solar cells (PSCs). Herein, for the first time we used the state‐of‐the‐art in situ liquid time‐of‐flight secondary ion mass spectrometry to molecularly explore the perovskite precursor solution chemistry. We identified that the methylammonium and formamidinium cations and the I− anion are the motivators of the aging chemistry. Further, we introduced two kinds of Lewis bases, triethyl phosphate (TP) and ethyl ethanesulfonate (EE), as new additives in the solution and unraveled that both of them can protect the reactive cations from aging through weak interactions. Significantly, TP is superior to EE in enhancing long‐term solution stability as it can well‐maintain the internal interaction structures within the solution phase. The PSC derived from a fresh TP‐doped solution delivered a high power conversion efficiency of 23.06 %, 92.23 % of which remained in that from a 21‐day‐old solution. In situ liquid time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is established as a molecular probe to unveil the aging chemistry of perovskite precursor solutions. In addition to uncovering the molecular mechanism of chemical aging reactions, it is demonstrated that the structure and stability difference of precursor‐additive interactions determines the anti‐aging effects of additives.