Modifying Perovskite Films with Polyvinylpyrrolidone for Ambient-Air-Stable Highly Bendable Solar Cells

A Stable Perovskite Sensitized Photonic Crystal P-N Junction with Enhanced Photoelectrochemical Hydrogen Production

The slow photon effect in inverse opal photonic crystals represents a promising approach to manipulate the interactions between light and matter through the design of material structures. This study introduces a novel ordered inverse opal photonic crystal (IOPC) sensitized with perovskite quantum dots (PQDs), demonstrating its efficacy for efficient visible-light-driven H2 generation via water splitting. The rational structural design contributes to enhanced light harvesting. The sensitization of the IOPC with PQDs improves optical response performance and enhances photocatalytic H2 generation under visible light irradiation compared to the IOPC alone. The designed photoanode exhibits a photocurrent density of 3.42 mA cm-2 at 1.23 V vs RHE. This work advances the rational design of visible light-responsive photocatalytic heterostructure materials based on wide band gap metal oxides for photoelectrochemical applications.

Raman Scattering Enhancement through Pseudo-Cavity Modes

Raman spectroscopy plays a pivotal role in spectroscopic investigations. The small Raman scattering cross-section of numerous analytes, however, requires enhancement of the signal through specific structuring of the electromagnetic and morphological properties of the underlying surface. This enhancement technique is known as surface-enhanced Raman spectroscopy (SERS). Despite the existence of various proposed alternatives, the approach involving Fabry-Pérot cavities, which constitutes a straightforward method to enhance the electromagnetic field around the analyte, has not been extensively utilized. This is because, for the analyte to experience the maximum electric field, it needs to be embedded within the cavity. Consequently, the top mirror of the cavity will eventually shield it from the external laser source. Recently, an open-cavity configuration has been demonstrated to exhibit properties similar to the classic Fabry-Pérot configuration, with the added advantage of maintaining direct accessibility for the laser source. This paper showcases how such a simple yet innovative configuration can be effectively utilized to achieve remarkable Raman enhancement. The simple structure, coupled with its inexpensive nature and versatility in material selection and scalability, makes it an ideal choice for various analytes and integration into diverse Raman apparatus setups.

Mechanical Durability and Flexibility in Perovskite Photovoltaics: Advancements and Applications

The remarkable progress in perovskite solar cell (PSC) technology has witnessed a remarkable leap in efficiency within the past decade. As this technology continues to mature, flexible PSCs (F-PSCs) are emerging as pivotal components for a wide array of applications, spanning from powering portable electronics and wearable devices to integrating seamlessly into electronic textiles and large-scale industrial roofing. F-PSCs characterized by their lightweight, mechanical flexibility, and adaptability for cost-effective roll-to-roll manufacturing, hold immense commercial potential. However, the persistent concerns regarding the overall stability and mechanical robustness of these devices loom large. This comprehensive review delves into recent strides made in enhancing the mechanical stability of F-PSCs. It covers a spectrum of crucial aspects, encompassing perovskite material optimization, precise crystal grain regulation, film quality enhancement, strategic interface engineering, innovational developed flexible transparent electrodes, judicious substrate selection, and the integration of various functional layers. By collating and analyzing these dedicated research endeavors, this review illuminates the current landscape of progress in addressing the challenges surrounding mechanical stability. Furthermore, it provides valuable insights into the persistent obstacles and bottlenecks that demand attention and innovative solutions in the field of F-PSCs.

Facile Vertical Structure Broadband Photodetectors Enabled by Polyvinylpyrrolidone-Regulated Perovskite and Near-Infrared-Sensitive Lead Phthalocyanine

Broadband photodetectors have drawn tremendous attention in many application areas such as imaging, optical communication, and biochemical sensing. Perovskite is a star material with broad spectral absorption, but it is challenging to develop ultraviolet-visible-near-infrared (UV-Vis-NIR) ultra-broadband photodetectors due to the insufficient absorption in the near-infrared region. Moreover, it is difficult to construct a diode-type photodetector with a simple vertical structure based only on perovskite materials. Here, facile vertical structure broadband photodetectors were fabricated based on heterojunctions that were composed of perovskite MAPbI3 films with UV-Vis absorption spectrum and small organic molecule lead phthalocyanine (PbPc) with strong NIR optical absorption, resulting in UV-Vis-NIR ultra-broadband photodetection. The quality of MAPbI3 films was improved by introducing polyvinylpyrrolidone (PVP) modification, and subsequently, the corresponding MAPbI3/PbPc heterojunction-based photodetectors exhibited rectification characteristics and reduced reverse dark currents. When the PVP mass ratio is 1 wt%, the photodetector achieved the best performance that the spectral response uniformity factor was as high as 0.77, the photoresponsivity exceeded 10 A/W, and the photoresponse time was less than 0.5 ms under a light intensity of 0.013 mW/cm2 in the UV-Vis to NIR spectral range. These results are comparable or superior to those of some inorganic, organic, and perovskite photodetectors reported previously. This study would provide an effective strategy to construct high-performance perovskite photodetectors based on a simple vertical structure, paving the way to the realization of UV-Vis-NIR broadband photodetection.

Progress and Challenges Toward Effective Flexible Perovskite Solar Cells

The demand for building-integrated photovoltaics and portable energy systems based on flexible photovoltaic technology such as perovskite embedded with exceptional flexibility and a superior power-to-mass ratio is enormous. The photoactive layer, i.e., the perovskite thin film, as a critical component of flexible perovskite solar cells (F-PSCs), still faces long-term stability issues when deformation occurs due to encountering temperature changes that also affect intrinsic rigidity. This literature investigation summarizes the main factors responsible for the rapid destruction of F-PSCs. We focus on long-term mechanical stability of F-PSCs together with the recent research protocols for improving this performance. Furthermore, we specify the progress in F-PSCs concerning precise design strategies of the functional layer to enhance the flexural endurance of perovskite films, such as internal stress engineering, grain boundary modification, self-healing strategy, and crystallization regulation. The existing challenges of oxygen-moisture stability and advanced encapsulation technologies of F-PSCs are also discussed. As concluding remarks, we propose our viewpoints on the large-scale commercial application of F-PSCs.

Simultaneously elevating the resistive switching level and ambient-air-stability of 3D perovskite (TAZ-H)PbBr3-based memory device by encapsulating into polyvinylpyrrolidone

The study about simultaneously enhancing the resistive switching level and ambient-air-stability of perovskite-based memorizers will promote its commercialization. Here, a new 3D perovskite (TAZ-H)PbBr₃ (TAZ-H⁺ = protonated thiazole) has been fabricated as FTO/(TAZ-H)PbBr₃/Ag device, which only exhibits binary memory performance with the high tolerant temperature of 170 °C. After encapsulating by polyvinylpyrrolidone (PVP), the (TAZ-H)PbBr₃@PVP composite-based device can demonstrate ternary resistive switching behavior with considerable ON2/ON1/OFF ratio (10^5.9: 10^3.9:1) and high ternary yield (68 %). Specially, this device presents good ambient-air stability at RH 80 % and thermal tolerance of 100 °C. The binary resistive switching mechanism can be ascribed to the halogen ion migration induced by bromine defects in the (PbBr₃)_n^n- framework. But the ternary resistive switching phenomenon in the (TAZ-H)PbBr₃@PVP-based device could be depicted as the carrier transport from filled traps of PVP to (PbBr₃)_n^n- framework (ON1 state) and then carriers flowing in the re-arranged (TAZ-H)_nⁿ⁺ chain in 3D channels (ON2 state). The PVP treatment can not only modify the grain boundary defects, but also facilitate the transport of injected carriers to the perovskite films via Pb-O coordinated bonds and inhibition of order-disorder transformation. This facial strategy for implementing ternary perovskite-based memorizers with good ambient-air-stability is quite meaningful for high-density memory in harsh environments.

Improved Thermal Stability and Film Uniformity of Halide Perovskite by Confinement Effect brought by Polymer Chains of Polyvinyl Pyrrolidone

Polyvinyl pyrrolidone (PVP) is doped to PbI₂ and organic salt during two-step growth of halideperovskite. It is observed that PVP molecules can interact with both PbI₂ and organic salt, reduce the aggregation and crystallization of the two, and then slow down the coarsening rate of perovskite. As doping concentration increases from 0 to 1 mM in organic salt, average crystallite size of perovskite decreases monotonously from 90 to 34 nm; Surface fluctuation reduces from 259.9 to 179.8 nm at first, and then increases; Similarly, surface roughness decreases from 45.55 to 26.64 nm at first, and then rises. Accordingly, a kind of "confinement effect" is resolved to crystallite growth and surface fluctuation/roughness, which helps to build compact and uniform perovskite film. Density of trap states (t-DOS) is cut down by ≈60% at moderate doping  (0.2 mM). Due to the "confinement effect", power conversion efficiency of perovskite solar cells is improved from 19.46 (±2.80) % to 21.50 (±0.99) %, and further improved to 24.11% after surface modification. Meanwhile, "confinement effect" strengthens crystallite/grain boundaries and improves thermal stability of both film and device. T₈₀ of device increases to 120 h, compared to 50 h for reference ones.

Functionalized polymer modified buried interface for enhanced efficiency and stability of perovskite solar cells

Although great progress has been made in perovskite solar cells (PCSs), further development of PCSs is hindered by a large number of defects, nonradiative recombination, and mysterious stresses. Here, we propose a new interfacial strategy by introducing a new polymer material named povidone-iodine (PV-I) as a buffer layer. A series of studies indicate that the introduced buffer layer can form a strong chemical interaction with SnO₂ and the perovskite, which can not only passivate the defects of the two functional layers but also strengthen the interfacial connection. The reduction of film defects and the enhancement of interface connection are beneficial to the extraction and transport of the carrier. In addition, the introduction of a buffer layer releases the interfacial stress. Ultimately, we achieved attractive efficiency (22.02%, 0.1 cm²) and considerable long-term stability (after aging 500 h, the target device still retains 81% of its original PCE). The excellent performance of the device indicates that this strategy can be used as an effective control method for perovskite solar cells to facilitate their commercialization.

Critical Size/Viscosity for Coffee-Ring-Free Printing of Perovskite Micro/Nanopatterns

Inkjet printing is the most encouraging method for patterning and integrating perovskite materials into microminiature application scenarios. However, it is still challenging to achieve high-resolution, coffee-ring-free, and perfect crystallized patterns. Here, a strategy based on powerful electrohydrodynamic printing and droplet viscosity-size coordinate regulation is developed to solve the above problems. By adding a long-chain polymer poly(vinylpyrrolidone) (PVP) into perovskite precursor to tune ink viscosity and introducing electrohydrodynamic printing to print the high-viscosity ink into droplets of different sizes, we can manipulate the inside flowing resistance and outside evaporation rate of a droplet, thus revealing a critical size/viscosity under which the coffee ring effect is inhibited, showing immense potential and significance for high-quality patterning. In addition, the long-chain polymer benefits droplet spatial limitation and uniform crystallization. The as-printed luminous patterns demonstrate high resolution (structure size ∼1 μm), excellent brightness, pleasant uniformity, and fascinating compatibility with flexible substrates, which is promising for future perovskite optoelectronic device applications.

Phthalide and 1-Iodooctadecane Synergistic Optimization for Highly Efficient and Stable Perovskite Solar Cells

The carrier non-radiative recombination and instability of device caused by the inherent defects are main factors limiting development of perovskite solar cells (PSCs). During the fabrication process of a PSC device, perovskite films often produce Pb⁰ and I⁰ defects. This paper reports a strategy for synergistic optimization of perovskite films by defects passivation and surface modification. The doping of phthalide (PT) in the Pb-rich (CH(NH₂ )₂ )_1-x (CH₃ NH₃ )_x PbI₃ film can passivate lead cation defects, and the modification of 1-iodooctadecane (1-IO) can reduce halogen anion defects and improve stability of PSCs owing to its hydrophobicity. The PT and 1-IO optimized device achieves a power conversion efficiency (PCE) of 22.27%. The optimized PSCs remain 93.2% of the initial PCE when placed in air environment (relative humidity of 10%, 25 °C) more than 70 days. The PT and 1-IO synergistic optimization provides a novel strategy for improving the performance and stability of PSCs.

Formamidinium Lead Iodide Perovskite Films with Polyvinylpyrrolidone Additive for Active Layer in Perovskite Solar Cells, Enhanced Stability and Electrical Conductivity

In this paper, we studied the influence of polyvinylpyrrolidone (PVP) as a stabilization additive on optical and electrical properties of perovskite formamidinium lead iodide (FAPI) polycrystalline thin films on ZnO nanorods (ZNR). FAPI (as an active layer) was deposited from a single solution on ZNR (low temperature processed electron transport layer) using a one-step method with the inclusion of an anti-solvent. The role of PVP in the formation of the active layer was investigated by scanning electron microscopy and contact angle measurements to observe the effect on morphology, while X-ray diffraction was used as a method to study the stability of the film in an ambient environment. The effect of the PVP additive on the optical and electrical properties of the perovskite thin films was studied via photoluminescence, UV-Vis measurements, and electrical impedance spectroscopy. We have demonstrated that PVP inclusion in solution-processed perovskite FAPI thin films prevents the degradation of the film in an ambient atmosphere after aging for 2 months. The inclusion of the PVP also improves the infiltration of FAPI perovskite into ZnO nanostructures, increases electrical conductivity and radiative recombination of the photo-generated charge carriers. These results show promising information for promoting PVP stabilized FAPI perovskites for the new generation of photovoltaic devices.

Inkjet Printability Assessment of Weakly Viscoelastic Fluid: A Semidilute Polyvinylpyrrolidone Solution Ink Case Study

Here, we present an integrated approach to the weakly viscoelastic fluid printability assessment by using global dimensionless criteria (DC). The problem was studied on a model semidiluted polyvinylpyrrolidone water-based ink. For the study purpose, the ink composition was kept as simple as possible. First, the solution density, viscosity, and surface tension were determined. Obtained data were used for testing limitations of DC printability diagrams already available for Newtonian fluids. A replotted version of the original Kim and Baek's map was developed emphasizing the importance of surface tension in the drop formation process. Another set of DC (e.g., Ec and De) was also used for a real evaluation of the viscoelasticity effect on both jetting conditions and drop formation. The polymer relaxation time as a crucial parameter for viscoelasticity was shown to be calculated using the Kuhn segment length rather than from Zimm and Rouse theories for diluted polymer systems. Then, a two-dimensional diagram using four DC (Oh and De with Ec and El as parameters) is proposed based on the famous McKinley's work. The diagram describes the interplay of possible forces responsible for filament thinning and breakup processes. Obtained results were supported by further experiments involving drop ejection and formation, determination of critical polymer concentration, and others. The proposed diagram promises a useful initial step in further investigations of viscoelasticity of polymer compounds by inkjet printing.

Enhanced Photovoltaic Properties of Perovskite Solar Cells by Employing Bathocuproine/Hydrophobic Polymer Films as Hole-Blocking/Electron-Transporting Interfacial Layers

In this study, we improved the photovoltaic (PV) properties and storage stabilities of inverted perovskite solar cells (PVSCs) based on methylammonium lead iodide (MAPbI3) by employing bathocuproine (BCP)/poly(methyl methacrylate) (PMMA) and BCP/polyvinylpyrrolidone (PVP) as hole-blocking and electron-transporting interfacial layers. The architecture of the PVSCs was indium tin oxide/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/MAPbI3/[6,6]-phenyl-C61-butyric acid methyl ester/BCP based interfacial layer/Ag. The presence of PMMA and PVP affected the morphological stability of the BCP and MAPbI3 layers. The storage-stability of the BCP/PMMA-based PVSCs was enhanced significantly relative to that of the corresponding unmodified BCP-based PVSC. Moreover, the PV performance of the BCP/PVP-based PVSCs was enhanced when compared with that of the unmodified BCP-based PVSC. Thus, incorporating hydrophobic polymers into BCP-based hole-blocking/electron-transporting interfacial layers can improve the PV performance and storage stability of PVSCs.

Flexible, ultra-stable and color tunable fluorescent films based on all inorganic perovskite quantum dots embedded in polymer

Colloidal perovskite CsPbX₃ (X = Cl, Br, I) nanocrystals (CPNCs)/polymers composites have attracted extensive attention due to their potential to be developed as flexible phosphor films for lighting applications. However, to maintain high quantum efficiency and photo stability of CPNCs in such composites remains a daunting challenge. Here, we have demonstrated a layered composite structure consisting of CPNCs and polydimethylsiloxane (PDMS) with multi-color emission and long-term stability. By tuning the molar ratio between CsPbCl_1.58Br_1.42 and CsPbBr_1.35I_1.65, flexible fluorescent films as down-converter layers with a high luminescent efficiency and a controllable color temperature spanning from 3194 K to 5901 K have been demonstrated. Furthermore, due to embedding inside such composites, the quantum efficiency of CPNCs exhibited negligible changes during seven months in ambient conditions. The carrier dynamics based on time-resolved photoluminescence (PL) and transient absorption spectroscopy reveal that the hot electron tunneling and trapping process are significant in the composite film. This work provides a good understanding of CPNC materials in complex composite for the development of flexible, robust, color controllable fluorescent films for lighting applications.

Nano-Micro Dimensional Structures of Fiber-Shaped Luminous Halide Perovskite Composites for Photonic and Optoelectronic Applications

Perovskite nanomaterials have been revealed as highly luminescent structures regarding their dimensional confinement. In particular, their promising potential lies behind remarkable luminescent properties, including color tunability, high photoluminescence quantum yield, and the narrow emission band of halide perovskite (HP) nanostructures for optoelectronic and photonic applications such as lightning and displaying operations. However, HP nanomaterials possess such drawbacks, including oxygen, moisture, temperature, or UV lights, which limit their practical applications. Recently, HP-containing polymer composite fibers have gained much attention owing to the spatial distribution and alignment of HPs with high mechanical strength and ambient stability in addition to their remarkable optical properties comparable to that of nanocrystals. In this review, the fabrication methods for preparing nano-microdimensional HP composite fiber structures are described. Various advantages of the luminescent composite nanofibers are also described, followed by their applications for photonic and optoelectronic devices including sensors, polarizers, waveguides, lasers, light-down converters, light-emitting diode operations, etc. Finally, future directions and remaining challenges of HP-based nanofibers are presented.

Improved photoemission and stability of 2D organic-inorganic lead iodide perovskite films by polymer passivation

2D organic-inorganic lead iodide perovskites hold great promise for functional optoelectronic devices. However, their performances have been seriously limited by poor long-term stability in ambient environment. Here, we perform a systematic study for the stability improvement of a typical 2D organic-inorganic lead iodide perovskite (PEA)2PbI4. The degradation of the (PEA)2PbI4 films can be attributed to the interaction with the humidity in environment, which leads to decomposition of the perovskite components. Then, we demonstrate that polymer passivation provides an effective approach for improving the crystal quality and stability of the (PEA)2PbI4 films. Correspondingly, the photoemission of the polymer-passivated (PEA)2PbI4 films has been enhanced due to the decreased trap states. More importantly, a hydrophobic polymer (Poly(4-Vinylpyridine), PVP) will protect the (PEA)2PbI4 films from humidity in ambient environment, which can greatly improve the physical and chemical stability of the 2D perovskite films. As a result, the PVP-passivated (PEA)2PbI4 films can produce a bright emission even after long-term (>15 d) exposure to ambient environment (25 °C, 80% RH) and continuous UV illumination. This work provides a convenient and effective approach for improving the long-term stability of 2D organic-inorganic lead iodide perovskites, which shows great promise for fabricating large-area and versatile optoelectronic devices.

Improving the Performance and Stability of Perovskite Light-Emitting Diodes by a Polymeric Nanothick Interlayer-Assisted Grain Control Process

CsPbBr₃ is a promising light-emitting material due to its wet solution processability, high photoluminescence quantum yield (PLQY), narrow color spectrum, and cost-effectiveness. Despite such advantages, the morphological defects, unsatisfactory carrier injection, and stability issues retard its widespread applications in light-emitting devices (LEDs). In this work, we demonstrated a facile and cost-effective method to improve the morphology, efficiency, and stability of the CsPbBr₃ emissive layer using a dual polymeric encapsulation governed by an interface-assisted grain control process (IAGCP). An eco-friendly low-cost hydrophilic polymer poly(vinylpyrrolidone) (PVP) was blended into the CsPbBr₃ precursor solution, which endows the prepared film with a better surface coverage with a smoothened surface. Furthermore, it is revealed that inserting a thin PVP nanothick interlayer at the poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/emissive layer interface further promotes the film quality and the performance of the derived LED. It is mainly attributed to three major consequences: (i) reduced grain size of the emissive layer, which facilitates charge recombination, (ii) reduced current leakage due to the enhanced electron-blocking effect, and (iii) improved color purity and air stability owing to better defect passivation. As a result, the optimized composite emissive film can retain the luminescence properties even on exposure to ambient conditions for 80 days and ∼62% of its initial PL intensity can be preserved after 30 days of storage without any encapsulation.

Magneto-Fluorescent Perovskite Nanocomposites for Directed Cell Motion and Imaging

The ability for a magnetic field to penetrate biological tissues without attenuation has led to significant interest in the use of magnetic nanoparticles for biomedical applications. In particular, active research is ongoing in the areas of magnetically guided drug delivery and magnetic hyperthermia treatment. However, the difficulties in tracing these optically nonactive magnetic nanoparticles hinder their usage in medical research or treatment. Here, a new perovskite-based magneto-fluorescent nanocomposite that allows the in situ, real-time optical visualization of magnetically induced cellular movements is reported. A swelling-deswelling technique is employed to capture a cesium lead halide perovskite and magnetite nanoparticles within a biocompatible polyvinylpyrrolidone matrix, to produce a water-dispersible composite that possesses a combination of strong magnetic response and intense fluorescence. The wavelength-tunability of perovskite nanocrystals is taken advantage of to demonstrate simultaneous multicolor fluorescent tagging of cancer stem cells. The magneto-directed motion of the cancer stem cells through a microfluidic channel is also imaged as a proof-of-concept toward an optically traceable magnetic manipulation of biological systems. These dual-functional nanocomposites could find promising applications in advanced biotechnologies, such as in optogenetics, cellular separation, and drug delivery studies.

Enhanced optoelectronic performance of 2D organic-inorganic hybrid perovskite through light-illumination

Improving the optoelectronic characteristics of organic-inorganic perovskites is crucial for fabrication of functional devices. Herein, we demonstrate that the optoelectronic properties of 2D organic-inorganic perovskites can be greatly improved by UV-light illumination during growth. The photoluminescence emission of the 2D perovskite exhibits a 3.1-folds increase in intensity, with a decreased trap-assisted recombination. The improved optoelectronic characteristics can be attributed to the high-quality crystallization and lattice expansion induced by the UV-light illumination. Moreover, the optimized 2D perovskites enable the fabrication of photoconductive devices with improved optoelectronic responses. This work indicates that light illumination is a novel and convenient approach for engineering the fabrication of 2D organic-inorganic hybrid perovskites, which advocates great promise for achieving high-performance functional devices.

Moisture-Resistant Electrospun Polymer Membranes for Efficient and Stable Fully Printable Perovskite Solar Cells Prepared in Humid Air

Fully printable perovskite solar cells (PPSCs) attract attention in the photovoltaic industry and research owing to their controllable and scalable production with reduced material waste during manufacturing. However, the commercialization of PPSCs has been impeded by their inherent vulnerability to ambient moisture, leading to a rapid loss of device efficiency and lifetime. Here, we propose a novel idea to enhance the photovoltaic performance and stability of PPSCs in humid air (relative humidity exceeding 80%) using electrospun hydrophobic polymer membranes, i.e., polylactic acid (PLA), polycaprolactone (PCL), and PLA/PCL blends, as moisture-resistant layers for PPSCs. After optimizing the morphologies, hydrophobicity, and thermal properties of the electrospun membranes by varying the contents of the polymer components in the membranes, the unencapsulated devices with these membranes demonstrated power conversion efficiencies of up to 8.2%, which was significantly higher than for devices without the membranes (6.8%). Moreover, devices with the optimum electrospun membrane retained more than 85% of their original efficiency after being stored in humid air for over 35 days. In comparison, devices without the electrospun membranes lost about 50% of their initial efficiency over the same time. Our work is very useful for the development of highly efficient and stable commercial PPSCs.

Flexible and Highly Durable Perovskite Solar Cells with a Sandwiched Device Structure

Flexible perovskite solar cells (PSCs) have been quickly developed as the most promising candidates for low-cost photovoltaic technology. However, the bendable and foldable properties of PSCs induce the decrease of their efficiencies. In this paper, we report the design of a new kind of flexible PSCs with a sandwiched structure. The critical layer of the flexible device is designed at a neutral layer of the sandwiched structure, which is stress-free, no matter how the device bending is. During the bending test, sandwich-structured flexible PSCs showed extremely long bending lifetime, which is at least 5-8 times higher than that of generally reported devices. At the same time, the sandwiched structure works as the encapsulation effect. The flexible device with a sandwiched structure greatly improves the device's long-term stability. Therefore, the designed sandwiched structure significantly promotes the bending ability and stability of flexible PSCs.