Enhanced Efficiency and Stability of All-Inorganic CsPbI2 Br Perovskite Solar Cells by Organic and Ionic Mixed Passivation

Mechanically Resilient and Highly Efficient Flexible Perovskite Solar Cells with Octylammonium Acetate for Surface Adhesion and Stress Relief

Flexible perovskite solar cells (FPSCs) have advanced significantly because of their excellent power-per-weight performance and affordable manufacturing costs. The unsatisfactory efficiency and mechanical stability of FPSCs are bottleneck challenges that limit their application. Here, we explore the use of octylammonium acetate (OAAc) with a long, intrinsic, flexible molecular chain on perovskite films for surface adhesion and mechanical releasing. The results showed that OAAc with high structural flexibility and strong molecular interactions can act as a mechanical release layer in releasing residual tensile stress, confirmed by the film and device characterizations as well as finite-element simulation. Moreover, the passivation of the OAAc could increase the formation energy of defects including I vacancy, Pb vacancy, and Pb-I antisite. The experimental results showed that the trap states of perovskites were significantly suppressed after OAAc modification, which is beneficial to the construction of high-quality films. With a high open-circuit voltage of 1.196 V, the efficiency of the OAAc-treated devices increased from 23.14% to 25.47% on a rigid substrate (23.12% on a flexible substrate), yielding superior long-term and mechanical durability. The corresponding flexible device retains 74% of the initial value even after 8000 bending cycles at a bending radius of 5 mm.

Effective Dual Cation Release in Quasi-2D Perovskites for Ultrafast UV Light-Powered Imaging

Ruddlesden-Popper quasi-2D perovskites represent robust candidates for optoelectronic applications, achieving a delicate balance between outstanding photoresponse and stability. However, mitigating the internal defects in polycrystalline films remains challenging, and their optoelectronic performances still lag behind that of their 3D counterparts. This work highlights the profound impact of defect passivation at the buried interface and grain boundaries through a dual-cation-release strategy. Cations released from the pre-deposited inorganic iodide buffer layer effectively repair deep-level defects by inducing low-dimensional phase reconstruction and interacting with undercoordinated ions. The resulting quasi-2D perovskite polycrystalline films feature large grain size (>2 µm) and minimum surface roughness, along with alleviated out-of-plane residual tensile strain, which is beneficial for inhibiting the initiation and propagation of cracks. The fabricated photodetector demonstrates drastically improved self-powered photoresponse capability, with maximum responsivity up to 0.41 A W-1 at 430 nm and an ultrafast response speed of 161 ns / 1.91 µs. Moreover, this strategy is compatible with the photolithography-assisted hydrophobic-hydrophilic patterning process for fabricating pixelated photodetector arrays, which enables high-sensitivity imaging. This study presents a feasible defect passivation approach in quasi-2D perovskites, thereby providing insights into the fabrication of high-performance optoelectronic devices.

Surface Regulation via Carboxylate Polymer for Efficient and Stable CsPbI2Br Perovskite Solar Cells

CsPbI2Br perovskite solar cell (PSC) is a promising candidate for high-efficiency single-junction and tandem solar cells. However, due to the numerous surface defects of the CsPbI2Br film and the mismatch of energy levels at the CsPbI2Br/charge transport layer interface, the power conversion efficiency (PCE) of CsPbI2Br PSC is still significantly lower than the theoretical limits. To alleviate those issues, in this work, a carboxylate-based p-type polymer, TTC-Cl, is employed to modify the surface of CsPbI2Br layer. TTC-Cl can interact with uncoordinated Pb2+, thereby mitigating surficial defects of CsPbI2Br film and reducing non-radiative recombination losses. Furthermore, TTC-Cl also improves the band properties of the CsPbI2Br thin film surface, rendering it more p-type, which facilitates hole transport. Consequently, the CsPbI2Br PSCs with TTC-Cl modification achieve a remarkable PCE of 17.81%, which is notably higher than that of counterpart without TTC-Cl (15.87%). Moreover, CsPbI2Br PSCs with TTC-Cl modification also exhibit better stability. This work highlights the importance of surface regulation via carboxylate polymer for further enhancing the performance of CsPbI2Br PSCs.

Ion migration in p-type perovskite MAPbI3 films under an electric field and thin-film transistor device failure

This study demonstrated a dynamic analysis to investigate the ion migration in p-type perovskite MAPbI3 films under an electric field, revealing its detrimental effects on the electrical performance of MAPbI3-based devices. An additive strategy was proposed to suppress ion migration, thereby facilitating the fabrication of high-performance MAPbI3-based devices.

Revealing the full potential of CsPbIBr2 perovskite solar cells: advancements towards enhanced performance

Cesium lead iodide bromide (CsPbIBr2) perovskite solar cells (PSCs) have improved stability compared to other perovskite compositions. However, they still face significant challenges due to their poor photovoltaic performance parameters, which limit the devices' power conversion efficiencies (PCEs). This study proposes a novel device design to tailor the potential of CsPbIBr2 PSCs by improving their optoelectronic properties. An advanced 3D multiphysics approach was rigorously used to investigate the optics and electrical properties of the proposed CsPbIBr2 PSCs. This approach combines finite-difference time-domain (FDTD) and finite element method (FEM) techniques with the particle swarm optimization (PSO) algorithm. The outcome from the adapted numerical approach is in good agreement with the experimental results. The optimized CsPbIBr2 PSC demonstrates a promising power conversion efficiency (PCE) of over 16.4%, associated VOC of 1.53 V, FF of 80.6%, and JSC of 13.4 mA cm-2. Therefore, the potential of CsPbIBr2 perovskites could be further explored with continued research and development in material science and device physics.

All-Inorganic Perovskite Solar Cells: Defect Regulation and Emerging Applications in Extreme Environments

All-inorganic perovskite solar cells (PSCs), such as CsPbX3, have garnered considerable attention recently, as they exhibit superior thermodynamic and optoelectronic stabilities compared to the organic-inorganic hybrid PSCs. However, the power conversion efficiency (PCE) of CsPbX3 PSCs is generally lower than that of organic-inorganic hybrid PSCs, as they contain higher defect densities at the interface and within the perovskite light-absorbing layers, resulting in higher non-radiative recombination and voltage loss. Consequently, defect regulation has been adopted as an important strategy to improve device performance and stability. This review aims to comprehensively summarize recent progresses on the defect regulation in CsPbX3 PSCs, as well as their cutting-edge applications in extreme scenarios. The underlying fundamental mechanisms leading to the defect formation in the crystal structure of CsPbX3 PSCs are firstly discussed, and an overview of literature-adopted defect regulation strategies in the context of interface, internal, and surface engineering is provided. Cutting-edge applications of CsPbX3 PSCs in extreme environments such as outer space and underwater situations are highlighted. Finally, a summary and outlook are presented on future directions for achieving higher efficiencies and superior stability in CsPbX3 PSCs.

Bifunctional interfacial engineering enabled efficient and stable carbon-based CsPbIBr2 perovskite solar cells

Carbon-based inorganic CsPbIBr2 perovskite solar cells (C-IPSC) have attracted widespread attention due to their low cost and excellent thermal stability. Unfortunately, due to the soft ion crystal nature of perovskite, inherent bulk defects and energy level mismatch at the CsPbIBr2/carbon interface limit the performance of the device. In this study, we introduced aromatic benzyltrimethylammonium chloride (BTACl) as a passivation layer to passivate the surface and grain boundaries of the CsPbIBr2 film. Due to the reduction of perovskite defects and better energy level arrangement, carrier recombination is effectively suppressed and hole extraction is improved. The champion device achieves a maximum power conversion efficiency (PCE) of 11.30% with reduces hysteresis and open circuit voltage loss. In addition, unencapsulated equipment exhibits excellent stability in ambient air.

Interface modification for efficient carbon-electrode CsPbI2Br perovskite solar cells using ionic liquid

All-inorganic CsPbI2Br, as a promising photovoltaic (PV) material, have attracted extensive research attention in society for its outstanding thermal stability and appropriate trade-offs. Carbon-based perovskite solar cells (C-PSCs) without hole transporting layer (HTL) have shown great potential in terms of cost-effectiveness and stability. However, the inevitable defects on the surface of CsPbI2Br films severely hampers the development of high-efficiency CsPbI2Br C-PSCs. Surface engineering has emerged an effective approach to overcome this challenge. Herein, 1-decyl-3-methylimidazolium tetrafluoroborate (DMTT) ionic liquid was introduced between CsPbI2Br and carbon electrode to reduce non-recombination of charges, decrease defect states, minimize the energy-level mismatch, and greatly enhance the device stability. As a result, the HTL-free CsPbI2Br C-PSCs combined with DMTT as an interface modification achieved a higher power conversion efficiency (PCE) of 12.47% than that of the control devices with a PCE of 11.32%. Furthermore, without any encapsulation, the DMTT-optimized C-PSC remained approximately 84% of its initial PCE after over 700 h under room temperature and 25% relative humidity (RH) conditions. Additionally, when exposed to a temperature of 65 °C for over 400 h, the device still retained 74% of the initial PCE, demonstrating its thermal stability.

Enhanced Efficiency and Stability of Inverted CsPbI2Br Perovskite Solar Cells via Fluorinated Organic Ammonium Salt Surface Passivation

All-inorganic perovskite solar cells (PSCs) have recently received increasing attention due to their outstanding thermal stability. However, the performance of these devices, especially for the devices with a p-i-n structure, is still inferior to that of the typical organic-inorganic counterparts. In this study, we introduce phenylammonium iodides with different side groups on the surface of the CsPbI2Br perovskite film and investigate their passivation effects. Our studies indicate that the 4-trifluoromethyl phenylammonium iodide (CFPA) molecule with the -CF3 side group effectively decreases the trap density of the perovskite film by forming interactions with the undercoordinated Pb2+ ions and significantly inhibits the nonradiative recombination in the derived PSC, leading to an enhanced open-circuit voltage (Voc) from 0.96 to 1.10 V after passivation. Also, the CFPA post-treatment enables better energy-level alignment between the conduction band minimum of CsPbI2Br perovskite and [6,6]-phenyl C61 butyric acid methyl ester, thereby enhancing the charge extraction from the perovskite to the charge transport layer. These combined benefits result in a significant enhancement of the power conversion efficiency from 11.22 to 14.37% for inverted CsPbI2Br PSCs. The device without encapsulation exhibits a degradation of only ≈4% after 1992 h in a N2 glovebox.

Recent Advances in Wide Bandgap Perovskite Solar Cells: Focus on Lead-Free Materials for Tandem Structures

A tandem solar cell, which is composed of a wide bandgap (WBG) top sub-cell and a narrow bandgap (NBG) bottom subcell, harnesses maximum photons in the wide spectral range, resulting in higher efficiency than single-junction solar cells. WBG (>1.6 eV) perovskites are currently being studied a lot based on lead mixed-halide perovskites, and the power conversion efficiency of lead mixed-halide WBG perovskite solar cells (PSCs) reaches 21.1%. Despite the excellent device performance of lead WBG PSCs, their commercialization is hampered by their Pb toxicity and low stability. Hence, lead-free, less toxic WBG perovskite absorbers are needed for constructing lead-free perovskite tandem solar cells. In this review, various strategies for achieving high-efficiency WBG lead-free PSCs are discussed, drawing inspiration from prior research on WBG lead-based PSCs. The existing issues of WBG perovskites such as VOC loss are discussed, and toxicity issues associated with lead-based perovskites are also addressed. Subsequently, the natures of lead-free WBG perovskites are reviewed, and recently emerged strategies to enhance device performance are proposed. Finally, their applications in lead-free all perovskite tandem solar cells are introduced. This review presents helpful guidelines for eco-friendly and high-efficiency lead-free all perovskite tandem solar cells.

Anion Exchange Ionomers: Design Considerations and Recent Advances - An Electrochemical Perspective

Alkaline-based electrochemical devices, such as anion exchange membrane (AEM) fuel cells and electrolyzers, are receiving increasing attention. However, while the catalysts and membrane are methodically studied, the ionomer is largely overlooked. In fact, most of the studies in alkaline electrolytes are conducted using the commercial proton exchange ionomer Nafion. The ionomer provides ionic conductivity; it is also essential for gas transport and water management, as well as for controlling the mechanical stability and the morphology of the catalyst layer. Moreover, the ionomer has distinct requirements that differ from those of anion-exchange membranes, such as a high gas permeability, and that depend on the specific electrode, such as water management. As a result, it is necessary to tailor the ionomer structure to the specific application in isolation and as part of the catalyst layer. In this review, an overview of the current state of the art for anion exchange ionomers is provided, summarizing their specific requirements and limitations in the context of AEM electrolyzers and fuel cells.

Operando dynamics of trapped carriers in perovskite solar cells observed via infrared optical activation spectroscopy

Conventional spectroscopies are not sufficiently selective to comprehensively understand the behaviour of trapped carriers in perovskite solar cells, particularly under their working conditions. Here we use infrared optical activation spectroscopy (i.e., pump-push-photocurrent), to observe the properties and real-time dynamics of trapped carriers within operando perovskite solar cells. We compare behaviour differences of trapped holes in pristine and surface-passivated FA0.99Cs0.01PbI3 devices using a combination of quasi-steady-state and nanosecond time-resolved pump-push-photocurrent, as well as kinetic and drift-diffusion models. We find a two-step trap-filling process: the rapid filling (~10 ns) of low-density traps in the bulk of perovskite, followed by the slower filling (~100 ns) of high-density traps at the perovskite/hole transport material interface. Surface passivation by n-octylammonium iodide dramatically reduces the number of trap states (~50 times), improving the device performance substantially. Moreover, the activation energy (~280 meV) of the dominant hole traps remains similar with and without surface passivation.

Preparation of High-Efficiency (>14%) HTL-Free Carbon-Based All-Inorganic Perovskite Solar Cells by Passivation with PABr Derivatives

Due to the advantages of low cost and good thermal stability, all-inorganic CsPbI2Br carbon-based perovskite solar cells (C-PSCs) without a hole transport layer have been rapidly developed in recent years. While the carbon electrode is in direct contact with the CsPbI2Br film, higher requirements are placed on the defects and energy level arrangement of the CsPbI2Br layer, which leads to the relatively low photoelectric conversion efficiency (PCE) of C-PSCs. Herein, propylamine hydrobromide (PABr) and its derivative 3-bromopropylamine hydrobromide (3Br-PABr) were used to passivate the surface defects of CsPbI2Br C-PSCs for the first time. The results show that passivation molecules are modulated by the substituent effect, leading to a stronger interaction between amino groups and uncoordinated Pb2+ ions, which facilitates a better passivation effect of 3Br-PABr. In addition, 3Br-PABr promotes the gradient arrangement of energy levels while passivating surface defects, which accelerates the rapid extraction of holes. After the passivation by PABr and 3Br-PABr, the PCE of HTL-free CsPbI2Br C-PSCs increased from 12.15% for the control device to 13.15 and 14.04%, respectively, which are among the highest reported values of CsPbI2Br C-PSCs.

Synergistic Effect of Surface p-Doping and Passivation Improves the Efficiency, Stability, and Reduces Lead Leakage in All-Inorganic CsPbIBr2 -Based Perovskite Solar Cells

Wide-bandgap inorganic cesium lead halide CsPbIBr₂ is a popular optoelectronic material that researchers are interested in because of the character that balances the power conversion efficiency and stability of solar cells. It also has great potential in semitransparent solar cells, indoor photovoltaics, and as a subcell for tandem solar cells. Although CsPbIBr₂ -based devices have achieved good performance, the open-circuit voltage (V_oc ) of CsPbIBr₂ -based perovskite solar cells (PSCs) is still lower, and it is critical to further reduce large energy losses (E_loss ). Herein, a strategy is proposed for achieving surface p-type doping for CsPbIBr₂ -based perovskite for the first time, using 1,5-Diaminopentane dihydroiodide at the perovskite surface to improve hole extraction efficiency. Meanwhile, the adjusted energy levels reduce E_loss and improve V_oc of the CsPbIBr₂ PSCs. Furthermore, the Cs- and Br-vacancies at the interface are filled, reducing structural disorder and defect states and thus improving the quality of the perovskite film. As a result, the target device achieves a high efficiency of 11.02% with a V_oc of 1.33 V, which is among the best values. In addition to the improved performance, the stability of the target device under various conditions is enhanced, and the lead leakage is effectively suppressed.

Enhancing Performance and Stability of Perovskite Solar Cells through Surface Defect Passivation with Organic Bidentate Lewis Bases

Organic Lewis bases [2,2'-bipyridine (BPY), 4-hydroxy-1,5-naphthyridine-3-carbonitrile (DQCN), and thenoyltrifluoroacetone (TTFA)] with bi-coordination sites of N and O were employed as perovskite surface defect passivants to address the efficiency and stability issues of perovskite solar cells (PSCs), with typical phenethylammonium iodide (PEAI) and piperazinium iodide (PI) passivants as reference. The surface properties of the perovskite films before and after passivation were characterized by Fourier-transform infrared, ultraviolet-visible, photoluminescence (PL), and time-resolved PL spectroscopy, X-ray diffraction, ultraviolet photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The characterizations reveal that BPY, DQCN, or TTFA forms coordination bonds with exposed "Pb2+", leading to a slight decrease in the highest occupied molecular orbital or lowest unoccupied molecular orbital energy level and bandgap. These passivants (especially TTFA) can passivate the perovskite surface defects to inhibit non-radiative recombination while having almost no influence on the grain size and surface morphology. Utilizing the passivated perovskite as the light absorption layer, solar cells with an inverted configuration of indium tin oxide/NiO x /passivated MAPbCl x I3-x /C60/BCP/Ag have been fabricated, and power conversion efficiencies of 19.22, 17.85, 16.49, 16.31, and 17.88% have been achieved from PEAI, PI, BPY, DQCN, and TTFA, respectively. All the device performance based on passivated perovskite is superior to that of the control (15.75%) owing to the reduced carrier recombination. The device from TTFA exhibits almost comparable efficiency to that of PEAI and PI controls, indicating that TTFA has an equal excellent passivation effect to state-of-the-art PEAI and PI. Furthermore, the devices based on BPY, DQCN, and TTFA show superior long-term stability with an efficiency loss of only 13.2, 16.7, and 12.9%, respectively, after being stored for 40 days in a ∼12% humidity, low-oxygen level environment, which is 45.4, 38.8, and 44.4% for the control, PEAI, and PI devices, respectively, primarily due to the improved hydrophobicity of the perovskite surface. Our results demonstrate that it is feasible to achieve high-efficiency and long-term-stable perovskite solar cells via selecting the appropriate molecules to passivate perovskite surface defects.

Ambient Spray Coating of Organic-Inorganic Composite Thin Films for Perovskite Solar Cell Encapsulation

Perovskite solar cells (PSCs) are developing rapidly in recent years, showing remarkable power conversion efficiency (PCE) of 25 %, which is comparable to crystalline silicon solar cells. However, since perovskite and other functional layers are very sensitive to the environment with high humidity, illumination, and heat, PSCs meet great challenges in device stability, which significantly limit their industrialization and commercialization. Encapsulation has become an effective strategy to enhance the stability of PSCs, and various encapsulation techniques have been developed, such as atomic layer deposition and glass-glass technology. Most of the current encapsulating methods are either time-consuming and sophisticated processes, or exhibit rigid configuration, which is unsuitable for flexible and curved devices. Here, an ambient spray coating method was developed to fabricate organic-inorganic composite film for direct encapsulation of PSCs. By systematical optimization of the film composition, thickness, and microstructures, a superhydrophobic encapsulating thin film with high compactness and homogeneity was achieved. As a result, the hybrid encapsulating film with polystyrene (PS)-4033/PS-4033-SiO₂ significantly improved the stability of PSCs in humid environment (60-70 % relative humidity, 35 °C) by showing about 10 times longer lifetime than that of the unencapsulated devices, which was mainly attributed to complementary effects from the high compactness of PS and high hydrophobicity of SiO₂ . This work suggests that direct deposition of organic-inorganic composite on devices as encapsulating films is an efficient strategy to enhance the device stability, and this method shows great promises of application in flexible and large-area devices.

Reveal the Humidity Effect on the Phase Pure CsPbBr3 Single Crystals Formation at Room Temperature and Its Application for Ultrahigh Sensitive X-Ray Detector

Generally, growing phase pure CsPbBr₃ single crystals is challenging, and CsPb₂ Br₅ or Cs₄ PbBr₆ by-products are usually formed due to the different solubilities of CsBr and PbBr₂ in the single solvent. Herein, the growth of high-quality phase pure CsPbBr₃ perovskite single crystals at room temperature by a humidity controlled solvent evaporation method is reported first. Meanwhile, the room temperature phase transition process from three dimensional (3D) cubic CsPbBr₃ to two dimensional (2D) layered tetragonal CsPb₂ Br₅ and the detailed mechanism induced by humidity are revealed. Moreover, compared with the organic-inorganic perovskite, the prepared CsPbBr₃ single crystals are much more stable under high humidity, which satisfies the long-term working conditions of X-ray detectors. The X-ray detectors based on CsPbBr₃ single crystals show a high sensitivity and a low detection limit of 1.89 μGy_air s^-1 , all of which meet the needs of medical diagnosis.