Layered 2D perovskites have been extensively investigated by scientists with photovoltaics (PV) expertise due to their good environmental stability. However, a random phase distribution in the perovskite film could affect both the performance and stability of the devices. To overcome this problem, we propose multifunctional interface engineering of 2D GA 2 MA 4 Pb 5 I 16 perovskite by employing guanidinium bromide (GABr) on top of it to optimize the secondary crystallization process. It is found that GABr treatment can facilitate to form a shiny and smooth surface of the 2D GA 2 MA 4 Pb 5 I 16 film with excellent optoelectronic properties. Thus, we realize efficient and stable 2D perovskite solar cells (PSCs) with a champion power conversion efficiency (PCE) of 19.3% under AM 1.5G illumination. Additionally, the optimized device without encapsulation could retain 94% of the initial PCE for more than 3000 h after being stored under ambient conditions.

HTMs with a planar core structure, extended-π system and electron-rich groups exhibited better intrinsic conductivity, which enhanced the photovoltaic performance.

Longevity is a long‐standing concern for organic–inorganic hybrid perovskite solar cells (PSCs). Recently, the use of low dimensional perovskite has been proven to be a promising strategy to improve the stability of PSCs. Herein, it is demonstrated that 1D perovskitoid based on 2‐diethylaminoethylchloride cations can act as a template to induce 1D@3D perovskite structure, leading to smoother surface texture, longer charge‐carrier lifetime, smaller residual tensile strain, and reduced surface‐defect density in the perovskite film. With this strategy, highly efficient and stable 1D@3D PSC with excellent reproducibility, showing a champion power conversion efficiency (PCE) of 22.9% under standard AM 1.5 G one sun illumination is realized. The unencapsulated optimized devices can retain 94.7%, 92.4%, and 90.0% of their initial PCEs for 2100, 2200, and 2200 h under ambient air, 85 °C and illumination conditions, respectively.

Organic–inorganic lead halide perovskite solar cells (PSCs) have demonstrated enormous potential as a new generation of solar‐based renewable energy. Although their power conversion efficiency (PCE) has been boosted to a spectacular record value, the long‐term stability of efficient PSCs is still the dominating concern that hinders their commercialization. Notably, interface engineering has been identified as a valid strategy with extraordinary achievements for enhancing both efficiency and stability of PSCs. Herein, the latest research advances of interface engineering for various interfaces are summarized, and the basic theory and multifaceted roles of interface engineering for optimizing device properties are analyzed. As a highlight, the authors provide their insights on the deposition strategy of interlayers, application of first‐principle calculation, and challenges and solutions of interface engineering for PSCs with high efficiency and stability toward future commercialization.

The quality of the perovskite film is crucial to the technological breakthrough of perovskite solar cells (PSCs). The two‐step method can facilitate the formation of a perovskite film with high quality and reproducibility. Many milestones have been made in the development of hybrid lead halide PSCs by using the two‐step method, which has a significant impact on their practical application. Herein, the reaction mechanism of the two‐step method including two‐step immersion method and two‐step spin coating method is summarized. The strategies such as component engineering, solvent engineering, and additive engineering of the two‐step method in preparing high‐quality films are introduced systematically and in detail. In addition, current issues of the two‐step method and its applications in lead‐free PSCs, all‐inorganic PSCs, large areas, and tandems are introduced and some suggestions are put forward for future research.