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Although much progress is made toward enhancing the efficiency of perovskite solar cells (PSCs), their operational reliability, particularly their mechanical stability, which is a crucial factor for flexible PSCs (f‐PCSs), has not attracted sufficient attention. The defects in the perovskite layer, especially on the top and the buried surface of the perovskite layer, can induce perovskite fracture, highly limiting the performance of f‐PSCs. Herein, a novel multifunctional organic salt, metformin hydrochloride, which can passivate cationic and anionic defects, is incorporated on both the top and buried surfaces of perovskite layer to suppress defects. As a result, a power conversion efficiency (PCE) of 24.40% for rigid PSCs and a PCE of 22.04% for f‐PSCs are achieved. Simultaneously, the device can retain 90% and 80% of the initial efficiency after 1000 h of light illumination and 10 000 bending cycles, respectively, showing excellent operational stability. This study may provide a global way to design a passivation strategy and fabricate flexible perovskite solar cells with high efficiency and stability. [ABSTRACT FROM AUTHOR]

Most of the high performance in perovskite solar cells (PSCs) have only been achieved with two organic hole transporting materials: 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9‐spirobifluorene (Spiro‐OMeTAD) and poly(triarylamine) (PTAA), but their high cost and low stability caused by the hygroscopic dopant greatly hinder the commercialization of PSCs. One effective alternative to address this problem is to utilize inexpensive inorganic hole transporting layer (i‐HTL), but obtaining high efficiency via i‐HTLs has remained a challenge. Herein, a well‐designed inorganic–organic double HTL is constructed by introducing an ultrathin polymer layer dithiophene‐benzene (DTB) between CuSCN and Au contact. This strategy not only enhances the hole extraction efficiency through the formation of cascaded energy levels, but also prevents the degradation of CuSCN caused by the reaction between CuSCN and Au electrode. Furthermore, the CuSCN layer also promotes the formation of a pinhole‐free and compact DTB over layer in the CuSCN/DTB structure. Consequently, the PSCs fabricated with this CuSCN/DTB layer achieves the power conversion efficiency of 22.0% (certified: 21.7%), which is among the top efficiencies for PSCs based on dopant‐free HTLs. Moreover, the fabricated PSCs exhibit high light stability under more than 1000 h of light illumination and excellent environmental stability at high temperature (85 °C) or high relative humidity (>60% RH). [ABSTRACT FROM AUTHOR]

Ruddlesden–Popper perovskite (RPP) materials have attracted great attention due to their superior stability, where the organic spacer dominantly determines the stability and efficiency of RPP solar cells, but research still lacks the systematical understanding of the interplay of binary spacer in the overall mixture range of 0–100% in RPPs on the precursor chemistry, film quality, and carrier behavior. Herein, a series of novel binary spacer RPP films of (PBA1−xBAx)2MA3Pb4I13 (BA = n‐butylammonium, PBA = 4‐phenylbutan‐1‐aminium, and MA = methylammonium) is successfully fabricated to reveal the interplay of binary spacers. The incorporation of 50% BA into the (PBA)2MA3Pb4I13 precursor solution increases the colloidal size and reduces nucleation sites, and therefore forms a very smooth film with much larger crystal grains and a higher degree of crystal preferential orientation, resulting in a significant reduction of trap states. The resulting combination of fast electron transfer and efficient electron extraction facilitates to effectively suppress the trap‐assisted charge recombination and remarkably decrease charge recombination losses. Consequently, the (PBA0.5BA0.5)2MA3Pb4I13 device achieves a champion efficiency of 16.0%, among the highest reported efficiencies for RPP devices. Furthermore, this device demonstrates good ambient, illumination, and thermal stabilities, retaining 60–93% of its initial efficiency after 30 days of various ageing. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are one of the most promising solar energy conversion technologies owing to their rapidly developing power conversion efficiency (PCE). Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, their application has been greatly hindered due to the lack of strategies to fabricate high‐quality electron transport layers (ETLs) at the low temperatures (≈100 °C) that most flexible plastic substrates can withstand, leading to poor performances for flexible PSCs. In this work, through combining the spin‐coating process with a hydrothermal treatment method, ligand‐free and highly crystalline SnO2 ETLs are successfully fabricated at low temperature. The flexible PSCs based on this SnO2 ETL exhibit an excellent PCE of 18.1% (certified 17.3%). The flexible PSCs maintained 85% of the initial PCE after 1000 bending cycles and over 90% of the initial PCE after being stored in ambient air for 30 days without encapsulation. The investigation reveals that hydrothermal treatment not only promotes the complete removal of organic surfactants coated onto the surface of the SnO2 nanoparticles by hot water vapor but also enhances crystallization through the high vapor pressure of water, leading to the formation of high‐quality SnO2 ETLs. [ABSTRACT FROM AUTHOR]