Incorporating mixed ion is a frequently used strategy to stabilize black-phase formamidinum lead iodide perovskite for high-efficiency solar cells. However, these devices commonly suffer from photoinduced phase segregation and humidity instability. Herein, we find that the underlying reason is that the mixed halide perovskites generally fail to grow into homogenous and high-crystalline film, due to the multiple pathways of crystal nucleation originating from various intermediate phases in the film-forming process. Therefore, we design a multifunctional fluorinated additive, which restrains the complicated intermediate phases and promotes orientated crystallization of α-phase of perovskite. Furthermore, the additives in-situ polymerize during the perovskite film formation and form a hydrogen-bonded network to stabilize α-phase. Remarkably, the polymerized additives endow a strongly hydrophobic effect to the bare perovskite film against liquid water for 5 min. The unencapsulated devices achieve 24.10% efficiency and maintain >95% of the initial efficiency for 1000 h under continuous sunlight soaking and for 2000 h at air ambient of ~50% humid, respectively.

Recently, organic–inorganic metal halide perovskite solar cells (PSCs) have achieved rapid improvement, however, the efficiencies are still behind the Shockley–Queisser theory mainly due to their high energy loss (ELOSS) in open‐circuit voltage (VOC). Due to the polycrystalline nature of the solution‐prepared perovskite films, defects at the grain boundaries as the non‐radiative recombination centers greatly affect the VOC and limit the device efficiency. Herein, poly(vinylidene fluoride) (PVDF) is introduced as polymer‐templates in the perovskite film, where the fluorine atoms in the PVDF network can form strong hydrogen‐bonds with organic cations and coordinate bonds with Pb2+. The strong interaction between PVDF and perovksite enables slow crystal growth and efficient defect passivation, which effectively reduce non‐radiation recombination and minimize ELOSS of VOC. PVDF‐based PSCs achieve a champion efficiency of 24.21% with a excellent voltage of 1.22 V, which is one of the highest VOC values reported for FAMAPb(I/Br)3‐based PSCs. Furthermore, the strong hydrophobic fluorine atoms in PVDF endow the device with excellent humidity stability, the unencapsulated solar cell maintain the initial efficiency of >90% for 2500 h under air ambient of ≈50% humid and a consistently high VOC of 1.20 V.

Although the power conversion efficiency values of perovskite solar cells continue to be refreshed, it is still far from the theoretical Shockley-Queisser limit. Two major issues need to be addressed, including disorder crystallization of perovskite and unbalanced interface charge extraction, which limit further improvements in device efficiency. Herein, we develop a thermally polymerized additive as the polymer template in the perovskite film, which can form monolithic perovskite grain and a unique “Mortise-Tenon” structure after spin-coating hole-transport layer. Importantly, the suppressed non-radiative recombination and balanced interface charge extraction benefit from high-quality perovskite crystals and Mortise-Tenon structure, resulting in enhanced open-circuit voltage and fill-factor of the device. The PSCs achieve certified efficiency of 24.55% and maintain >95% initial efficiency over 1100 h in accordance with the ISOS-L-2 protocol, as well as excellent endurance according to the ISOS-D-3 accelerated aging test.

To date, numbers of polymeric hole-transporting materials (HTMs) have been developed to improve interfacial charge transport to achieve high-performance inverted perovskite solar cells (PSCs). However, molecular design for passivating the underlying surface defects between perovskite and HTMs is a neglected issue, which is a major bottleneck to further enhance the performance of the inverted devices. Herein, we design and synthesize a new polymeric HTM PsTA-mPV with the methylthiol group, in which a lone pair of electrons of sulfur atoms can passivate the underlying interface defects of the perovskite more efficiently by coordinating Pb 2+ vacancies. Furthermore, PsTA-mPV exhibits a deeper highest occupied molecular orbital (HOMO) level aligned with perovskite due to the π-acceptor capability of sulfur, which improves interfacial charge transfer between perovskite and the HTM layer. Using PsTA-mPV as a dopant-free HTM, the inverted PSCs show 20.2% efficiency and long-term stability, which is ascribed to surface defect passivation, well energy-level matching with perovskite, and efficient charge extraction.