Benefiting from the booming development of self-assembled monolayer (SAM) based hole-transporting materials, inverted perovskite solar cells (PSCs) have attained a certified power conversion efficiency (PCE) beyond 27.0%, exhibiting great potential for commercialization. However, conventional SAM molecules are prone to self-aggregation owing to their inherent molecular configurations, which readily induced defective and inhomogeneous deposition. In addition, state-of-the-art SAM-based hole-transporting layers are generally deposited in inert environments, while the ambient moisture is expected to further deteriorate the homogeneity of the SAM layers. In this work, a mixed-solvent system of ethanol/N,N-dimethylformamide (DMF) was adopted for the deposition of Me-4PACz SAMs in ambient conditions, which enables significant suppression of intermolecular aggregation in precursor solution and moisture-induced inhomogeneity. The high-quality homogeneous SAM-based hole-transporting layers, along with subsequently optimized perovskite buried interface properties, further empower a prominent increase in the PCE of inverted PSC devices up to 25.0%.

Effective passivation of bulk and interface defects is one of the key drivers for achieving highly efficient and stable p-i-n perovskite solar cells (PSCs). Despite the versatility of bulky ammonium cations in defect passivation, ionic migration of these cations under light and thermal stresses is undesirable for maintaining the integrity of the passivation layer and thus detrimental to the device performance and long-term stability. To address this issue, a stepwise passivation approach employing 2-methoxyphenylethylammonium (2-MeO-PEA⁺) cation and piperazine dihydroiodide (PipDI) is proposed. By integrating bulk incorporation and subsequent surface treatment, the passivation approach synergistically mitigates both bulk and interface defects, and thereby enhances the resilience of the perovskite layer against light and thermal stresses. Owing to the significantly improved morphology, crystallinity, and optoelectronic properties of the perovskite layer, a champion PSC device with a PCE of 26.10% and outstanding stability is achieved, demonstrating the feasibility of the proposed two-step passivation approach.