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.

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.

Pure FAPbI3 (where FA is formamidinium) based perovskite solar cells (PSCs) have drawn tremendous attention because of their exceptional photovoltaic properties, although long-term stability is still a big challenge. Molecular tailoring is one of the practical approaches to enhancing the stability of FAPbI3 by passivating the film defects; however, deep understanding of how the molecular configuration affects the adjacent layer in FAPbI3 PSCs is urgently needed. Herein, we report a strategy of molecularly tailoring the FAPbI3/SnO2 interface by employing three Li salts by varying the anion configurations (CO3 2–, C2O4 2–, and HCOO–). When C–O and C=O groups are in optimal configuration, they will form the strongest bonds with uncoordinated Sn4+ and FA+, respectively, which can increase the formation energy of VFA defects, release the residual stress of the FAPbI3 lattice, facilitate the charge transport at the FAPbI3/SnO2 interface, and improve the stability of the PSC. Consequently, we obtained a champion device with a power conversion efficiency of 23.5%, and the unencapsulated device can maintain good stability under continuous light illumination.

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Novel poly­(vinyl alcohols) (PVA) functionalized with pendant thermo- and pH-responsive groups were prepared by carbonyl­diimidazole (CDI)-mediated couplings of N 1,N 1-diethylethane-1,2-diamine (DEEDA) with controllable modification degree. Nuclear magnetic response (NMR) and IR have verified the successful modification of PVA. The macro- and microscopic phase transition behavior of the obtained PVA-DEEDA-t (t = 10, 30, 70, and 90 h) was thoroughly characterized using various techniques, including turbidity measurement, NMR, and dynamic light scattering (DLS). PVA-DEEDA-t is demonstrated to possess tunable lower critical solution temperature (LCST) between 58 and 24 °C. LCST is dependent on solution pH and degree of PVA modification (14.1–20.9%). By combining DLS and DOSY characterizations, it can be concluded that both coil-to-globule transition and aggregation occurred to PVA-DEEDA-t during phase transition, while only coil-to-globule transition can be detected for the pristine PVA. 2D NOESY proved that the −NH– segment on PVA-DEEDA-t is in close (<5 Å) proximity to the main chain of PVA, as evidenced by the appearance of NOE signal between −NH– on DEEDA and −CH2–CH– chain of PVA when the temperature increased above LCST. To exploit the functional applications, the PVA-DEEDA-90 h was transformed into gel and film forms. PVA-DEEDA-90 h gel obtained by adding borax enabled controlled drug (e.g., RhB) release due to its temperature- and pH-dependent permeability. The PVA-DEEDA-90 h film was also casted on ITO glass, creating a smart surface with tunable wettability and interfacial ion transportation with high sensitivity toward the pH and temperature.

All‐inorganic perovskites have attracted substantial interest due to their outstanding thermal stability. However, the device performance is still inferior to the typical organic–inorganic counterparts because of the unsatisfying phase stability and defects of the inorganic perovskite films. Herein, a multistrategy to optimize CsPbI2Br perovskite solar cells (PSCs) based on dopant‐free poly(3‐hexylthiophene) (P3HT) by applying thienylmethylamine acetate additive to enhance the α phase stability and passivate the bulk defects of CsPbI2Br perovskite is successfully demonstrated, followed by implementing BTCIC‐4Cl interlayer at CsPbI2Br/P3HT interface, which can coordinate with both perovskite and P3HT to suppress the surface defects and promote the hole transport. Benefitting from these, a champion power conversion efficiency (PCE) of 16.3% is achieved, and the unencapsulated optimized device can retain 97% of the initial PCE after aging under N2 atmosphere at 85 °C for 530 h. This work opens up a new era of multistrategy for improving performance and stability of CsPbI2Br PSCs based on dopant‐free hole transport layer.

It is known that the perovskite/hole transport layer (HTL) interface is a great limit to achieving high-performance perovskite solar cells (PSCs). Aiming to solve this problem, we introduce a naphthalene diimide (NDI)-based conjugated polymer bearing 3,4-difluorothiophene (PTzNDI-2FT) at the perovskite/HTL interface. We find that the PTzNDI-2FT interlayer combines multifunctions to passivate surface defects on the perovskite film, improve charge transport at the perovskite/HTL interface, and prevent penetration of the moisture and organic ion volatilization in the perovskite film. The champion device exhibits a power conversion efficiency of 23.2% under standard AM 1.5 G one sun illumination and offers excellent environmental, heat, and light stabilities.

Intensive efforts have been devoted to the synthesis of thermoresponsive polymers with terminal N-alkyl-substituted groups.