Multi-functional cyclic ammonium chloride additive for efficient and stable air-processed perovskite solar cells

Because morphology and defect of organic-inorganic halide perovskite film is very sensitive to moisture and oxygen, it is important to develop humidity tolerant air-processes that produce high quality film with minimal defects for the successful commercialization of perovskite solar cells (PeSCs). As an attempt to optimize perovskite film in the air, we develop a cyclic quaternary ammonium chloride (N-(2-hydroxyethyl)-N-methylpyrrolidinium chloride, M-P chloride) with a pentagonal ring and hydroxyl functional group as an effective additive. The Cl⁻ anions in M-P chloride increase the crystallinity and the grain size by retarding nucleation and growth rate. After crystal growth, bulky M-P chloride diffuses out and remains on the grain boundaries and surface of the perovskite, and thus passivates both types of defects. Furthermore, since the M-P chloride may act as a moisture absorber, the intermediate phase of the perovskite can be protected from the moisture. As a result, this strategy can not only modulate the crystallinity and film morphology but also passivate the defects, leading to enhanced efficiency and stability, regardless of humidity. In particular, even at high humidity of ∼77%, PeSC with M-P chloride exhibits 18.20% power conversion efficiency (PCE) without any hysteresis behavior.