Advanced photovoltaics, such as ultra-flexible perovskite solar cells (UF-PSCs), which are known for their lightweight design and high power-to-mass ratio, have been a long-standing goal that we, as humans, have continuously pursued. Unlike normal PSCs fabricated on rigid substrates, producing high-efficiency UF-PSCs remains a challenge due to the difficulty in achieving full coverage and minimizing defects of metal halide perovskite (MHP) films. In this study, we utilized Al2O3 nanoparticles (NPs) as an inorganic surface modifier to enhance the wettability and reduce the roughness of poly-bis(4-phenyl) (2,4,6-trimethylphenyl) amine simultaneously. This approach proves essentials in fabricating UF-PSCs, enabling the deposition of uniform and dense MHP films with full coverage and fewer defects. We systematically investigated the effect of Al2O3 NPs on film formation, combining simulation with experiments. Our strategy not only significantly increases the power conversion efficiency (PCE) from 11.96% to 16.33%, but also promotes reproducibility by effectively addressing the short circuit issue commonly encountered in UF-PSCs. Additionally, our UF-PSCs demonstrates good mechanical stability, maintaining 98.6% and 79.0% of their initial PCEs after 10,000 bending cycles with radii of 1.0 and 0.5 mm, respectively.

Flexible perovskite solar cells (f‐PSCs) show great promise in portable‐power applications (e.g., chargers, drones) and low‐cost, scalable productions (e.g., roll‐to‐roll). However, in conventional n–i–p architecture f‐PSCs, the low‐temperature processed metal oxide electron transport layers (ETLs) usually suffer from high resistance and severe defects that limit the power conversion efficiency (PCE) improvement of f‐PSCs. Besides the enhancement in the mobility of metal oxide and passivation for perovskite/ETL interfacial defects reported in previous literature, herein, the electron transport loss between the metal oxide nanocrystallines within the ETL is studied by introducing an amorphous F‐doped TiO x (F‐TiO x ) caulked crystalline SnO 2 composite ETL. The F‐TiO x in this novel composite ETL acts as an interstitial medium between adjacent SnO 2 nanocrystallines, which can provide more electron transport channels, effectively passivate oxygen vacancies, and optimize the energy level arrangement, thus significantly enhancing the electron mobility of ETL and reducing the charge transport losses. The composite ETL‐based f‐PSCs achieve a high PCE of 22.70% and good operational stability. Furthermore, a moderate roughness of the composite ETL endows f‐PSCs with superior mechanical reliability by virtue of a strong coupling at the ETL/perovskite interface, by which the f‐PSCs can maintain 82.11% of their initial PCE after 4000 bending cycles.

Antisolvent engineering is routinely used to modulate the crystallization of perovskite films as they can offer an additional driving force for nucleation. Actually, the intervention of antisolvent into nucleation is thought to involve some relatively fast and complex processes, which, however, are not fully understood so far. Here, the diffusion of the organic amine cation FA+ (one dominated precursor) and its distribution in a spin-coating process in different antisolvents is simulated by the computational fluid dynamics (CFD) model. It is suggested that a moderate diffusion rate (like that in the case of toluene as an antisolvent) not only enables to form a very uniform distribution of FA+ ions on the substrate, beneficial to the uniform nucleation of the intermediate phase, but also can balance the nucleation and growth rates of the intermediate phase, thereby suppressing undesired heterogeneous nucleation and growth. Results show that the perovskite film fabricated using toluene as an antisolvent has a high quality, based on which higher power conversion efficiencies of up to 24.32% are achieved for perovskite solar cells.

Interfacial passivation engineering plays a crucial role in the explosive development of perovskite solar cells (PSCs). However, previous studies on passivation layers mainly focused on the defect-passivation mechanism rather than the interfacial charge transport efficiency. Here, by precisely tuning the interplanar spacing of the ammonium iodide passivation layer, we elucidate the promoting effect of the reduced interplanar spacing of the passivation layer on the photogenerated hole tunneling efficiency at the interface of the hole transport layer and perovskite. Compared with the commonly used phenethylammonium iodide passivation layer with a wider interplanar spacing, 2-chlorobenzylammonium iodide with a narrower interplanar spacing can help break through the thickness limitation of the passivation layer, thus showing a better comprehensive passivation effect. Therefore, we demonstrate photovoltaic devices with an enhanced fill factor (FF) and open-circuit voltage (VOC), which yield a high power conversion efficiency (PCE) of up to 23.1%. We thus identify an efficient scheme to achieve optimal passivation conditions for high-performance PSCs.

Precise control of the growth of 2D perovskites on 3D perovskites to form “trans-grain boundaries” 2D/3D structure for the preparation of flexible perovskite solar cells with a certified PCE up to 22.1% and excellent mechanical stability.