B-Site Co-Doping Coupled with Additive Passivation Pushes the Efficiency of Pb-Sn Mixed Inorganic Perovskite Solar Cells to Over 17

Pb-Sn mixed inorganic perovskite solar cells (PSCs) have garnered increasing interest as a viable solution to mitigate the thermal instability and lead toxicity of hybrid lead-based PSCs. However, the relatively poor structural stability and low device efficiency hinder its further development. Herein, high-performance manganese (Mn)-doped Pb-Sn-Mn-based inorganic perovskite solar cells (PSCs) are successfully developed by introducing Benzhydroxamic Acid (BHA) as multifunctional additive. The incorporation of smaller divalent Mn cations contributes to a contraction of the perovskite crystal, leading to an improvement in structural stability. The BHA additive containing a reductive hydroxamic acid group (O═C-NHOH) not only mitigates the notorious oxidation of Sn2+ but also interacts with metal ions at the B-site and passivates related defects. This results in films with high crystallinity and low defect density. Moreover, the BHA molecules tend to introduce a near-vertical dipole moment that parallels the built-in electric field, thus facilitating charge carrier extraction. Consequently, the resulting device delivers a champion PCE as high as 17.12%, which represents the highest reported efficiency for Pb-Sn-based inorganic PSCs thus far. Furthermore, the BHA molecule provides an in situ encapsulation of the perovskite grain boundary, resulting in significant enhancement of device air stability.

Facile Hydrogen-Bonding Assisted Crystallization Modulation for Large-area High-quality CsPbI2 Br Films and Efficient Solar Cells

The thermally stable inorganic cesium-based perovskites promise efficient and stable photovoltaics. Unfortunately, the strong ionic bonds lead to uncontrollable rapid crystallization, making it difficult in fabricating large-area black-phase film for photovoltaics. Herein, we developed a facile hydrogen-bonding assisted strategy for modulating the crystallization of CsPbI2 Br to achieve uniform large-area phase-pure films with much-reduced defects. The simple addition of methylamine acetate in precursors not only promotes the formation of intermediate phase via hydrogen bonding to circumvent the direct crystallization of CsPbI2 Br from ionic precursors but also widens the film processing window, thus enabling to fabricate large-area high-quality phase-pure CsPbI2 Br film under benign conditions. Combining with stable dopant-free poly(3-hexylthiophene), the CsPbI2 Br solar cells achieve the record-high efficiencies of 18.14 % and 16.46 % for 0.1 cm2 and 1 cm2 active area, respectively. The obtained high efficiency of 38.24 % under 1000 lux illumination suggests its potential in indoor photovoltaics for powering the Internet of Things, etc.

Enhancing Stability and Efficiency of Inverted Inorganic Perovskite Solar Cells with In-Situ Interfacial Cross-Linked Modifier

Inverted inorganic perovskite solar cells (PSCs) is potential as the top cells in tandem configurations, owing to the ideal bandgap, good thermal and light stability of inorganic perovskites. However, challenges such as mismatch of energy levels between charge transport layer and perovskite, significant non-radiative recombination caused by surface defects, and poor water stability have led to the urgent need for further improvement in the performance of inverted inorganic PSCs. Herein, the fabrication of efficient and stable CsPbI3-x Brx PSCs through surface treatment of (3-mercaptopropyl) trimethoxysilane (MPTS), is reported. The silane groups in MPTS can in situ crosslink in the presence of moisture to build a 3-dimensional (3D) network by Si-O-Si bonds, which forms a hydrophobic layer on perovskite surface to inhibit water invasion. Additionally, -SH can strongly interact with the undercoordinated Pb2+ at the perovskite surface, effectively minimizing interfacial charge recombination. Consequently, the efficiency of the inverted inorganic PSCs improves dramatically from 19.0% to 21.0% under 100 mW cm-2 illumination with MPTS treatment. Remarkably, perovskite films with crosslinked MPTS exhibit superior stability when soaking in water. The optimized PSC maintains 91% of its initial efficiency after aging 1000 h in ambient atmosphere, and 86% in 800 h of operational stability testing.

Limitations and Progresses in Carbon-Based Cesium Lead Halide Perovskite Solar Cells

Inorganic cesium lead halide perovskites (CsPbIx Br3-x , 0≤x≤3) are promising alternatives with great thermal stability. Additionally, the choice of moisture-resistive and dopant-free carbon as the electrode material can simultaneously solve the problems of stability and cost. Therefore, carbon electrode-based inorganic PSCs (C-IPSCs) represent a promising candidate for commercialization, yet both the efficiencies and stability of related devices demand further progress. This article reviews the recent advancement of C-IPSCs and then unravels the distinctive merits and limitations in this field. Subsequently, our perspective on various modification strategies is analyzed on a methodological level. Finally, this article outlooks the promising research contents and the remaining unresolved issues in this field. We believe that understanding and analyzing the related problems in this field are instructive to stimulate the future development of C-IPSCs.

Strengthened Surface Modification for High-Performance Inorganic Perovskite Solar Cells with 21.3% Efficiency

Metal halide inorganic perovskites show excellent thermal stability compared to organic-inorganic perovskites. However, the performance of inorganic perovskite solar cells (PSCs) is far from theoretical values, together with unsatisfactory stability, mainly due to the poor interfacial properties. In this work, a facial but effective method is reported to realize high-performance inorganic PSCs by post-modifying the perovskite surface with 2-thiophene ethylamine (TEA). It is found that amine group from TEA can favorably interact with the undercoordinated Pb2+ via Lewis acid-based coordination, while thiophene ring with electron-rich sulfur assists such interaction by functioning as an electron donor. The synergetic interaction allows TEA to passivate perovskite film defects more efficiently, as compared to phenethylamine (PEA) with less electron-donating ability. Moreover, perovskite valence band is slightly upward shift to match with hole transport material and facilitate hole transfer. These combinations result in a reduced non-radiative charge recombination and improved charge carrier lifetime. Consequently, PSCs with TEA modification shows a drastic improvement of VOC by 54 mV, yielding a champion PCE of 21.3%, much higher than the control PSCs (19.3%), along with improved ambient stability. This work demonstrates that surface modifier with an electron-rich moiety is critical for achieving efficient and stable inorganic PSCs.

Stabilization of Inorganic Perovskite Solar Cells with a 2D Dion-Jacobson Passivating Layer

Inorganic metal halide perovskites such as CsPbI3 are promising for high-performance, reproducible, and robust solar cells. However, inorganic perovskites are sensitive to humidity, which causes the transformation from the black phase to the yellow δ, non-perovskite phase. Such phase instability has been a significant challenge to long-term operational stability. Here, a surface dimensionality reduction strategy is reported, using 2-(4-aminophenyl)ethylamine cation to construct a Dion-Jacobson 2D phase that covers the surface of the 3D inorganic perovskite structure. The Dion-Jacobson layer mainly grows at the grain boundaries of the perovskite, effectively passivating surface defects and providing favourable interfacial charge transfer. The resulting inorganic perovskite films exhibit excellent humidity resistance when submerged in an aqueous solution (isopropanol:water = 4:1 v/v) and exposed to a 50% humidity air atmosphere. The Dion-Jacobson 2D/3D inorganic perovskite solar cell (PSC) achieves a power conversion efficiency (PCE) of 19.5% with a Voc of 1.197 eV. It retains 83% of its initial PCE after 1260 h of maximum power point tracking under 1.2 sun illumination. The work demonstrates an effective way for stabilizing efficient inorganic perovskite solar cells.

Electronic Structure and Optical Properties of Inorganic Pm3m and Pnma CsPbX3 (X = Cl, Br, I) Perovskite: A Theoretical Understanding from Density Functional Theory Calculations

In this study, we investigated the optoelectronic properties of cubic (Pm3m) and orthorhombic (Pnma) CsPbX3 (X = I, Br, and Cl). We utilized the full potential linear augmented plane wave method, which is implemented in the WIEN2k code, to facilitate the investigation. Different exchange potentials were used to analyze the optoelectronic behavior using the available density functional theory methods. Our findings revealed that CsPbX3 perovskites display direct band gaps at the R and Г points for cubic (Pm3m) and orthorhombic (Pnma) structures, respectively. Among the exchange potentials, the mBJ-GGA method provided the most accurate results. These outcomes concurred with the experimental results. In both Pm3m and Pnma structures, interesting changes were observed when iodide (I) was replaced with bromine (Br) and then chlorine (Cl). The direct band gap at the R and Г points shifted to higher energy levels. Similarly, when I was replaced with Br and Cl, there was a noticeable decrease in the absorption coefficient, dielectric constants, refractive index, and reflectivity, in addition to a band gap shift to higher energy levels.

Control of Halogen Atom in Inorganic Metal-Halide Perovskites Enables Large Piezoelectricity for Electromechanical Energy Generation

Regulating the strain of inorganic perovskites has emerged as a critical approach to control their electronic and optical properties. Here, an alternative strategy to further control the piezoelectric properties by substituting the halogen atom (I/Br) in the CsPbX3 perovskite (X = Cl, Br) structure is adopted. A series of piezoelectric materials with excellent piezoelectric coefficients (d33 ) are unveiled. Iodine-incorporated CsPbBr2 I demonstrates the record intrinsic piezoelectric response (d33 ≈47 pC N-1 ) among all inorganic metal halide perovskites. This leads to an excellent electrical output power of ≈ 0.375 mW (24.8 µW cm-2 N-1 ) in the piezoelectric energy generator (PEG) which is higher than those of the pristine/mixed perovskite references with CsPbX3 (X = I, Br, Cl). With its structural phase remaining unchanged, the strained CsPbBr2 I retains its superior piezoelectricity in both thin film and nanocrystal powder forms, further demonstrating its repeatability and versatility of applications. The origin of high piezoelectricity is found to be due to halogen-induced anisotropic lattice strain in the unit-cell along the c-axis, and octahedral distortion. This study reveals an avenue to design new piezoelectric materials by modifying their halide constituents and paves the way to design efficient PEGs for improved electromechanical energy conversion.

Surface Modification in CsPb0.5Sn0.5I2Br Inorganic Perovskite Solar Cells: Effects of Bifunctional Dipolar Molecules on Photovoltaic Performance

Inorganic tin-lead binary perovskites have piqued the interest of researchers as effective absorbers for thermally stable solar cells. However, the nonradiative recombination originating from the surface undercoordinated Sn²⁺ cations and the energetic offsets between different layers cause an excessive energy loss and deteriorate the perovskite device's performance. In this study, we investigated two thioamide derivatives that differ only in the polar part connected to their common benzene ring, namely, benzenecarbothioamide and 4-fluorophenylcarbothioamide (F-TBA). These two molecules were implemented as modifiers onto the inorganic tin-lead perovskite (CsPb_0.5Sn_0.5I₂Br) surface in the perovskite solar cells. Modifiers that carry C═S and NH₂ functional groups, equipped with lone electron pairs, can autonomously associate with surface Sn²⁺ through coordination and electrostatic attraction mechanisms. This interaction serves effectively to passivate the surface. In addition, due to the permanent dipole moment of the intermediate layer, an interfacial dipole field appears at the PCBM/CsPb_0.5Sn_0.5I₂Br interface, reducing the electron extraction potential barrier. Consequently, the planar solar cell with an ITO/PEDOT:PSS/CsPb_0.5Sn_0.5I₂Br/PCBM/BCP/Ag layered structure featuring an F-TBA surface post-treatment demonstrated a noteworthy power conversion efficiency of 14.01%. Simultaneously, after being stored for 1000 h in an inert atmosphere glovebox, the non-encapsulated CsPb_0.5Sn_0.5I₂Br solar cells managed to preserve 94% of their original efficiency.

Perovskite-Based X-ray Detectors

X-ray detection has widespread applications in medical diagnosis, non-destructive industrial radiography and safety inspection, and especially, medical diagnosis realized by medical X-ray detectors is presenting an increasing demand. Perovskite materials are excellent candidates for high-energy radiation detection based on their promising material properties such as excellent carrier transport capability and high effective atomic number. In this review paper, we introduce X-ray detectors using all kinds of halide perovskite materials along with various crystal structures and discuss their device performance in detail. Single-crystal perovskite was first fabricated as an active material for X-ray detectors, having excellent performance under X-ray illumination due to its superior photoelectric properties of X-ray attenuation with μm thickness. The X-ray detector based on inorganic perovskite shows good environmental stability and high X-ray sensitivity. Owing to anisotropic carrier transport capability, two-dimensional layered perovskites with a preferred orientation parallel to the substrate can effectively suppress the dark current of the device despite poor light response to X-rays, resulting in lower sensitivity for the device. Double perovskite applied for X-ray detectors shows better attenuation of X-rays due to the introduction of high-atomic-numbered elements. Additionally, its stable crystal structure can effectively lower the dark current of X-ray detectors. Environmentally friendly lead-free perovskite exhibits potential application in X-ray detectors by virtue of its high attenuation of X-rays. In the last section, we specifically introduce the up-scaling process technology for fabricating large-area and thick perovskite films for X-ray detectors, which is critical for the commercialization and mass production of perovskite-based X-ray detectors.

Fabrication of High-Quality CsPbI3 Perovskite Films with Phosphorus Pentachloride Additive for Highly Stable Solar Cells

Fully inorganic perovskite cesium lead triiodide (CsPbI₃ ) has garnered much attention from researcher for photovoltaic application because of its excellent thermal stability compared with the inorganic-organic hybrid counterparts, along with the potential to serve as the top cell in tandem devices with silicon solar cell. However, the active α-phase cubic CsPbI₃ spontaneously tends to transform into the non-perovskite δ-CsPbI₃ when subjected to ambient condition. This work proposes an effective method to fabricate high-quality and stable α-phase cubic CsPbI₃ films by introducing phosphorus pentachloride (PCl₅ ) as an additive. PCl₅ acts as colloidal binder for modulating crystallization dynamics of perovskites, resulting in high-quality film and a significantly suppressed phase transition. Finally, highly stable CsPbI₃ perovskite solar cells can be achieved with a power conversion efficiency up to 17.85 %, and a long-term stability in N₂ filled glove box.

Effect of Interface Modification on Mechanoluminescence-Inorganic Perovskite Impact Sensors

It is becoming increasingly important to develop innovative self-powered, low-cost, and flexible sensors with the potential for structural health monitoring (SHM) applications. The mechanoluminescence (ML)-perovskite sensor is a potential candidate that combines the light-emitting principles of mechanoluminescence with the light-absorbing properties of perovskite materials. Continuous in-situ SHM with embedded sensors necessitates long-term stability. A highly stable cesium lead bromide photodetector with a carbon-based electrode and a zinc sulfide (ZnS): copper (Cu) ML layer was described in this article. The addition of a magnesium iodide (MgI₂) interfacial modifier layer between the electron transport layer (ETL) and the Perovskite interface improved the sensor's performance. Devices with the modified structure outperformed devices without the addition of MgI₂ in terms of response time and impact-sensing applications.

Flexible Self-Powered Weak Light Detectors Based on ZnO/CsPbBr3/γ-CuI Heterojunctions

Halide perovskites (HPs) with marvelous optical and electrical properties are regarded as one of the competitive candidates for building next-generation photodetectors (PDs). However, combining their excellent properties with satisfactory long-term robustness is still challenging, ultimately limiting the practical applications of HP-based PDs. Herein, a high vacuum deposition system is employed to fabricate flexible self-powered PDs with a ZnO/CsPbBr₃/γ-CuI structure, which shows excellent stability and outstanding performance in weak light detection. Benefiting from the improved crystallinity and optimized device structure, a high detectivity of 8.1 × 10¹³ Jones and a rapid response speed (rise/decay time of 3.9/1.8 μs) are obtained in this self-powered device. Furthermore, the unencapsulated device exhibits intriguing environmental stability and mechanical flexibility. The photocurrent remains unchanged after 7000 s of continuous operation or 100 bending cycles. Furthermore, a 15 × 15 PD array is fabricated as an image sensor. A high contrast image of the target object can be obtained owing to the high sensitivity and uniformity of the self-powered PDs. These results demonstrate the feasibility and practicality of the ZnO/CsPbBr₃/γ-CuI heterojunction for applications in weak light detection and image formation.

Synchronous Surface Reconstruction and Defect Passivation for High-Performance Inorganic Perovskite Solar Cells

The nonradiative charge recombination caused by surface defects and inferior crystalline quality are major roadblocks to further enhancing the performance of CsPbI_{3- x} Br_x perovskite solar cells (PSCs). Theoretical calculations indicate that sodium diethyldithiocarbamate (NaDDTC), a popular bacteriostatic benign material, can initiate multiple interactions with the CsPbI_{3- x} Br_x perovskite surface to effectively passivate the defects. The experimental results reveal that the NaDDTC can indeed passivate the electron trap states and lock active sites for charge traps and water adsorption. In addition, it is found that a solid-state reaction is triggered for perovskite crystal regrowth by the NaDDTC post-treatment, which not only enlarges grain size for reducing the density of grain boundary defects but also compensates some surface defects induced by the primary film growth. Consequently, the power conversion efficiency (PCE) of the CsPbI_{3- x} Br_x PSC is increased to as high as 20.40%, with significant improvement in fill factor and open-circuit voltage (V_OC ), making it one of the highest for this type of solar cell. Furthermore, the optimized devices exhibit better environmental stability. Overall, this robust synchronous strategy provides efficient surface reconstruction and defect passivation for achieving both high PCE and stable inorganic perovskite.

CsPbI3-Based Phase-Stable 2D Ruddlesden-Popper Perovskites for Efficient Solar Cells

Inorganic CsPbI₃ perovskite has shown great promise in highly stable perovskite solar cells due to the lack of volatile organic components. However, the inferior phase stability in ambient conditions resulted from the very small Cs⁺, limiting their practical applications. Here, CsPbI₃-based 2D Ruddlesden-Popper (RP) perovskites were developed using two thiophene-based aromatic spacers, namely, 2-thiophenemethylamine hydroiodide (ThMA) and 2-thiopheneformamidine hydroiodide (ThFA), which significantly improved the phase stability by releasing the large inner stress of black-phase CsPbI₃. The optimized ThFA-based 2D RP perovskite (n = 5, ThFA-Cs) device achieves a record efficiency of 16.00%. Importantly, the ThFA-Cs devices could maintain an average of 98% of their initial efficiencies after being stored in N₂ at room temperature for 3000 h and 92% of their initial value at 80 °C for 960 h. This work provides a new perspective for exploration of the phase-stable CsPbI₃-based perovskite with reduced dimensions for high-performance solar cells.

All-Inorganic Perovskite Solar Cells with Tetrabutylammonium Acetate as the Buffer Layer between the SnO2 Electron Transport Film and CsPbI3

All-inorganic CsPbI₃ perovskites have great potential in tandem cells in combination with other photovoltaic devices. However, CsPbI₃ perovskite solar cells (PSCs) still face a huge challenge, resulting in a low power conversion efficiency (PCE) relative to organic-inorganic PSCs. In this work, we introduced tetrabutylammonium acetate (TBAAc) as a buffer layer between the SnO₂ electron-transport layer (ETL) and CsPbI₃ all-inorganic perovskite film interface for the first time. TBAAc not only improved the conductivity of SnO₂ ETL but also formed a 1D TBAPbI₃ layer between the SnO₂ ETL and the 3D CsPbI₃ all-inorganic perovskite film, thereby enhancing the stability and passivating the surface defects of the CsPbI₃ perovskite to fabricate high-efficiency carbon-counter electrode (CE)-based CsPbI₃ solar cells. We fabricated carbon-CE-based hole-transporting layer ( HTL)-free PSCs with an FTO/SnO₂/TBAAc/CsPbI₃/C structure. The open-circuit voltage (V_oc), short circuit current density (J_sc), PCE, and fill factor of the champion CsPbI₃ PSCs simultaneously enhanced to 1.08 V, 17.48 mA/cm², 12.79, and 67.8%, respectively. This PCE is currently one of the high efficiencies reported for the above planar-structured carbon-CE-based CsPbI₃ PSCs to date. Moreover, the optimized device exhibits excellent stability, which retained over 83% of its initial PCE after 350 h. This work provides a facile way of simultaneous optimization of the SnO₂ ETL and the CsPbI₃ perovskite layer to fabricate stable and high-efficiency carbon-CE-based CsPbI₃ PSCs.

p-Type Carbon Dots for Effective Surface Optimization for Near-Record-Efficiency CsPbI2 Br Solar Cells

Interface modification to minimize charge recombination and trapping for efficient charge transport is crucial for the performance of perovskite solar cells (PSCs). Herein, functionalized p-type blue carbon dots (B-CDs) are ventured as an interface passivation layer to enhance the efficiency and long-term stability of all-inorganic CsPbI₂ Br PSCs. It is found that first the blue carbon dots with abundant NH, CN, CO, and CO functional groups effectively passivate defects by reacting with I^- and Pb²⁺ ions in the perovskite through hydrogen and coordinative bonds. Second, the p-type B-CDs modifiers form a P-N junction with the n-type perovskite to provide efficient pathways for hole transfer and electron blocking. Third, the B-CDs increase the hydrophobicity of the perovskite film to improve the stability of CsPbI₂ Br PSCs. With the above advantages, the CsPbI₂ Br PSC with B-CDs modification shows an efficiency as high as 16.76%, one of the highest for its type. In addition, the modification renders significant improvement of air and light stability, with 95.33% of the initial PCE retained after storage in the ambient environment for 1000 h. This work demonstrates the great potential of B-CDs application in perovskite-based optoelectronic devices.

Electrical Loss Management by Molecularly Manipulating Dopant-free Poly(3-hexylthiophene) towards 16.93 % CsPbI2 Br Solar Cells

Inorganic cesium lead halide perovskites offer a pathway towards thermally stable photovoltaics. However, moisture-induced phase degradation restricts the application of hole transport layers (HTLs) with hygroscopic dopants. Dopant-free HTLs fail to realize efficient photovoltaics due to severe electrical loss. Herein, we developed an electrical loss management strategy by manipulating poly(3-hexylthiophene) with a small molecule, i.e., SMe-TATPyr. The developed P3HT/SMe-TATPyr HTL shows a three-time increase of carrier mobility owing to breaking the long-range ordering of "edge-on" P3HT and inducing the formation of "face-on" clusters, over 50 % decrease of the perovskite surface defect density, and a reduced voltage loss at the perovskite/HTL interface because of favorable energy level alignment. The CsPbI₂ Br perovskite solar cell demonstrates a record-high efficiency of 16.93 % for dopant-free HTL, and superior moisture and thermal stability by maintaining 96 % efficiency at low-humidity condition (10-25 % R. H.) for 1500 hours and over 95 % efficiency after annealing at 85 °C for 1000 hours.

Electrochemical Deposition of CsPbBr3 Perovskite for Photovoltaic Devices with Robust Ambient Stability

Alkali halide perovskites have emerged as representative candidates for novel opto-electronic devices owing to their balanced efficiency and stability. However, their fabrication method still remains a challenging topic with conflicts among their effectiveness, complexity, and cost. Herein, a complete two-step electrochemical method has been applied in the fabrication of inorganic perovskites for the first time. The dimension and microstructure of CsPbBr₃ can be easily controlled by variation of simple physical parameters during the fabrication. By optimizing the parameters, high-quality CsPbBr₃ films are obtained, and the champion device has achieved an efficiency of 7.86% with a high open-circuit voltage of 1.43 V. More importantly, the as-fabricated materials have shown an extraordinary robust stability against environmental conditions even after 150 days of exposure to air without encapsulation. This has evidently proved the electrochemical methods as an effective route for perovskite synthesis in its future development.

Chemically Stable Black Phase CsPbI3 Inorganic Perovskites for High-Efficiency Photovoltaics

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high-efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI₃ with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single-junction and tandem solar cells. Comparing to the anisotropic organic cations, the isotropic cesium cation without hydrogen bond and cation orientation renders CsPbI₃ exhibit unique optoelectronic properties. However, the unideal tolerance factor of CsPbI₃ induces the challenges of different crystal phase competition and room temperature phase stability. Herein, the latest important developments regarding understanding of the crystal structure and phase of CsPbI₃ perovskite are presented. The development of various solution chemistry approaches for depositing high-quality phase-pure CsPbI₃ perovskite is summarized. Furthermore, some important phase stabilization strategies for black phase CsPbI₃ are discussed. The latest experimental and theoretical studies on the fundamental physical properties of photoactive phase CsPbI₃ have deepened the understanding of inorganic perovskites. The future development and research directions toward achieving highly stable CsPbI₃ materials will further advance inorganic perovskite for highly stable and efficient photovoltaics.

Ultrasensitive UV Photodetector Based on Interfacial Charge-Controlled Inorganic Perovskite-Polymer Hybrid Structure

In this work, we demonstrate an ultrasensitive, visible-blind ultraviolet (UV) photodetector based on perovskite-polymer hybrid structure. A novel wide-band-gap vacancy-ordered lead-free inorganic perovskite Cs₂SnCl₆ with Nd³⁺ doping is employed in the active layer of this hybrid photodetector. Remarkably, with interfacial charge-controlled hole-injection operating mechanism, our device achieves a maximum detectivity of 6.3 × 10¹⁵ Jones at 372 nm, fast photoresponse speed with rise time and fall time in the order of milliseconds, and a large linear dynamic range of 118 dB. The performance is significantly better than most of the existing organic and inorganic semiconductor UV photodetectors reported so far, and its detectivity is close to 1 order of magnitude higher than that of the photomultiplication tube (PMT) in the UV region. In addition, the photodetector demonstrated excellent environmental stability, which is critical for commercial deployment of perovskite-based optoelectronic devices. The results presented in this work open a new route toward development of high-performance optoelectronic devices using perovskite-based hybrid nanomaterial systems.

CsPbI2Br Perovskite Solar Cells Based on Carbon Black-Containing Counter Electrodes

CsPbI₂Br perovskite solar cells (PSCs) based on carbon electrodes (CEs) are considered to be low-cost and thermally stable devices. Nevertheless, the insufficient contact and energy level mismatch between the CsPbI₂Br layer and CE hinder the further enhancement of the cell efficiency. Herein, a carbon black (CB) interlayer was introduced between the perovskite layer and CE. The hole extraction was facilitated due to the larger contact area and suitable energy band alignment in the CsPbI₂Br/CB interface. Further investigation indicated the diffusion of CB nanoparticles from the CE or CB layer to the CsPbI₂Br film after a certain period of time. We disclosed the formation of a CB-CsPbI₂Br bulk heterojunction structure due to the carbon diffusion, which resulted in an efficiency enhancement. As a result, a record efficiency of 13.13% is achieved for carbon-based inorganic PSCs. This work also reveals that the diffusion of CB nanoparticles in CB-containing PSCs is universal and inevitable, although this kind of diffusion results in the enhancement of cell efficiency.

High Phase Stability in CsPbI3 Enabled by Pb-I Octahedra Anchors for Efficient Inorganic Perovskite Photovoltaics

CsPbI₃ inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI₃ severely hinders its applications. Herein, the nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI₃ . CsPbI₃ is decorated with multifunctional 4-aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr-CsPbI₃ (ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI₃ anchors the PbI₆ octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner-sharing PbI₆ octahedra and kinetically stabilizes the photoactive phase CsPbI₃ . Moreover, the added ABA and NGBr not only interact with shallow- or deep-level defects in CsPbI₃ to significantly reduce defect density, but also lead to improved energy-level alignment at the interfaces between the CsPbI₃ and the charge transport layers. Finally, the champion NGBr-CsPbI₃ (ABA)-based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase-stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.

Efficient All-Inorganic Perovskite Light-Emitting Diodes with Improved Operation Stability

Stability is becoming a main issue for perovskite light-emitting diodes (PeLEDs), as their external quantum efficiency (EQE) has been boosted to above 20%. An all-inorganic perovskite, cesium lead iodide (CsPbI₃), has better stability than organic-inorganic hybrid perovskites but suffers from a transition to yellow δ-CsPbI₃ phase at room temperature. Herein, we report stabilization of the α-CsPbI₃ phase by in situ formation of perovskite nanocrystals (NCs). By incorporation of a proper ratio of bulky organoammonium halides, 4-fluoro-phenylmethylammonium iodide (4-F-PMAI), stable α-CsPbI₃ films with nanometer-sized crystals can be obtained using a one-step spin-coating approach. The PeLEDs using α-CsPbI₃ NC films as emitters show a pure red emission at 692 nm and a high EQE of 14.8%. The EQE is further boosted to 18.6% using CsPbI_2.8Br_0.2 as the emissive layer. Furthermore, the PeLEDs show a very decent half-lifetime of over 1200 min and a shelf stability of over 2 months, much longer than that of hybrid PeLEDs.

Inverse Growth of Large-Grain-Size and Stable Inorganic Perovskite Micronanowire Photodetectors

Control of forward and inverse reactions between perovskites and precursor materials is key to attaining high-quality perovskite materials. Many techniques focus on synthesizing nanostructured CsPbX₃ materials (e.g., nanowires) via a forward reaction (CsX + PbX₂ → CsPbX₃). However, low solubility of inorganic perovskites and complex phase transition make it difficult to realize the precise control of composition and length of nanowires using the conventional forward approach. Herein, we report the self-assembly inverse growth of CsPbBr₃ micronanowires (MWs) (CsPb₂Br₅ → CsPbBr₃ + PbBr₂↑) by controlling phase transition from CsPb₂Br₅ to CsPbBr₃. The two-dimensional (2D) structure of CsPb₂Br₅ serves as nucleation sites to induce initial CsPbBr₃ MW growth. Also, phase transition allows crystal rearrangement and slows down crystal growth, which facilitates the MW growth of CsPbBr₃ crystals along the 2D planes of CsPb₂Br₅. A CsPbBr₃ MW photodetector constructed based on the inverse growth shows a high responsivity of 6.44 A W^-1 and detectivity of ∼10¹² Jones. Large grain size, high crystallinity, and large thickness can effectively alleviate decomposition/degradation of perovskites, which leads to storage stability for over 60 days in humid environment (relative humidity = 45%) and operational stability for over 3000 min under illumination (wavelength = 400 nm, light intensity = 20.06 mW cm^-2).

High-Quality Conformal Homogeneous All-Vacuum Deposited CsPbCl3 Thin Films and Their UV Photodiode Applications

A sensitive and fast ultraviolet (UV) photodetector is strongly desirable because of its wide range of applications in chemical/biological sensing and imaging. CsPbCl₃-based thin film photodetectors have not been constructed previously owing to their extremely poor precursor solubility; however, vapor deposition allows for thin film fabrication without the limitation of solubility. Therefore, this work is the first to demonstrate the optoelectronic properties of inorganic CsPbCl₃ perovskite thin films and UV photodiodes using all-vacuum deposition. The perovskites annealed at 120 °C exhibited outstanding performance, including a notable external quantum efficiency value of 797.1% with an applied bias of -2 V, an outstanding detectivity of 1.4 × 10¹³ Jones, a short response time as low as ∼ 50 μs, and a large linear dynamic range of up to 136 dB. CsPbCl₃ thin films manufactured by this vacuum-deposited approach were also found to be moisture-resistant and demonstrated high durability. The devices maintained excellent performance and demonstrated less than 10% degradation after 30 days. Thus, thin film visible-blind UV detectors can potentially be used in transparent smart displays, window-integrated electronic circuits, and sensor applications.

All-Inorganic Perovskite Solar Cells Based on CsPbIBr2 and Metal Oxide Transport Layers with Improved Stability

Despite the successful improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs), the issue of instability is still a serious challenge for their commercial application. The issue of the PSCs mainly originates from the decomposition of the organic–inorganic hybrid perovskite materials, which will degrade upon humidity and suffer from the thermal environment. In addition, the charge transport layers also influence the stability of the whole devices. In this study, inorganic transport layers are utilized in an inverted structure of PSCs employing CsPbIBr₂ as light absorbent layer, in which nickel oxide (NiO_x) and cerium oxide (CeO_x) films are applied as the hole transport layer (HTL) and the electron transport layer (ETL), respectively. The inorganic transport layers are expected to protect the CsPbIBr₂ film from the contact of moisture and react with the metal electrode, thus preventing degradation. The PSC with all inorganic components, inorganic perovskite and inorganic transport layers demonstrates an initial PCE of 5.60% and retains 5.56% after 600 s in ambient air at maximum power point tracking.

Thermally Stable Inorganic CsPbI2Br Mesoscopic Metal Halide Perovskite Solar Submodules

Highly efficient and thermally stable inorganic CsPbI₂Br mesoscopic metal halide perovskite (MHP) solar cells with a poly-3-hexylthiophene (P3HT) hole transporting layer (HTL) are demonstrated by spin-washing of the P3HT HTL since the light harvesting efficiency is improved by minimizing the coabsorption of light by P3HT, and the open-circuit voltage is enhanced because of the increased valence band maximum position of the spin-washed P3HT HTL. The spin-washed CsPbI₂Br MHP solar cell exhibited 1.24 V open-circuit voltage (V_oc), 14.20 mA/cm² short-circuit current density (J_sc), 81.52% fill factor (FF), and 14.35% power conversion efficiency (PCE). The unencapsulated spin-washed CsPbI₂Br MHP solar cell went through 7.56% degradation after a 1000 h thermal stability test under 100 °C/25% relative humidity (RH) and simultaneous 1 sun light soaking conditions. In addition, the unencapsulated spin-washed CsPbI₂Br MHP solar submodule with 25 cm² of masked active area showed a 98% geometrical FF, 115.09 mA short-circuit current, 3.54 V V_oc, 71.09% FF, and 11.58% PCE while exhibiting 8.80% of degradation during a thermal stability test at 100 °C/25% RH and 1 sun light soaking for 1000 h.

A 0D/3D Heterostructured All-Inorganic Halide Perovskite Solar Cell with High Performance and Enhanced Phase Stability

Although organic-inorganic hybrid perovskite solar cells (PVSCs) have achieved dramatic improvement in device efficiency, their long-term stability remains a major concern prior to commercialization. To address this issue, extensive research efforts are dedicated to exploiting all-inorganic PVSCs by using cesium (Cs)-based perovskite materials, such as α-CsPbI₃ . However, the black-phase CsPbI₃ (cubic α-CsPbI₃ and orthorhombic γ-CsPbI₃ phases) is not stable at room temperature, and it tends to convert to the nonperovskite δ-CsPbI₃ phase. Here, a simple yet effective approach is described to prepare stable black-phase CsPbI₃ by forming a heterostructure comprising 0D Cs₄ PbI₆ and γ-CsPbI₃ through tuning the stoichiometry of the precursors between CsI and PbI. Such heterostructure is manifested to enable the realization of a stable all-inorganic PVSC with a high power conversion efficiency of 16.39%. This work provides a new perspective for developing high-performance and stable all-inorganic PVSCs.

Enhancing the Phase Stability of Inorganic α-CsPbI3 by the Bication-Conjugated Organic Molecule for Efficient Perovskite Solar Cells

Inorganic CsPbI₃ perovskite has demonstrated promising potentials for photovoltaic applications, whereas the black perovskite polymorph (α phase) of CsPbI₃ was easily prone to converting into yellow phase (δ phase) under ambient moist environment, which restrained its practical application and further studies severely. In this study, p-phenylenediammonium iodide (PPDI) was employed to posttreat CsPbI₃ films for controlling the phase conversion, strengthening moisture resistance, and improving device performance. The multiple roles of PPDI were as follows: (1) avoiding spontaneous octahedral tilting by ionic bonds between NH₃⁺ of PPD²⁺ and I^- of [PbI₆]^4-; (2) enhancing the hydrophobicity induced by exactly exposed oil-wet (hydrophobic) benzene rings; and (3) passivating surface defects and filling I vacancies. As a result, after the treatment, mutable a-CsPbI₃ could maintain its α phase for at least 30 d in dry air (<20% RH). The perovskite solar cells with PPDI treatment exhibited reproductive photovoltaic performance with a champion power conversion efficiency (PCE) of 10.4, and 91% of the initial PCE was retained after storage for 504 h in a dark dry box without any encapsulation.

Stable and Strong Emission CsPbBr3 Quantum Dots by Surface Engineering for High-Performance Optoelectronic Films

We demonstrated complete surface passivation of CsPbBr₃ quantum dots (QDs) by treatment with di-dodecyldimethylammonium bromide (DDAB) and sodium thiocyanate (NaSCN), resulting in dispersions with photostable photoluminescence of near-unity quantum yield (∼100%) as well as high carrier mobility of QDs' film. Br^- from DDAB and SCN^- from NaSCN passivated the bromine vacancies of the QDs to reduce the surface defect density and increase the stability. The QDs-passivated maintained the original photoluminescence intensity under ultraviolet irradiation from a 150 W xenon lamp for 1 h, whereas the PL intensity of QDs-control dropped quickly to 20% of its initial value. The shorter DDA⁺ ligands also improved carrier transport in the QDs-passivated film, which was verified by conductivity and space charge limited current measurements. When used as the photoemitting species in a solution-processed light-emitting diode structure, the surface treatment increased the maximum luminance from 550 to 1200 cd·m^-2 and reduced the turn-on voltage from 3.1 to 2.8 V.

White Light-Emitting Devices Based on Inorganic Perovskite and Organic Materials

Perovskite-based materials have attracted considerable attention in photoelectric devices. In this paper, we report the one-step fabrication of spin-coated CsPbBr_2.5I_0.5 perovskite films doped with PAN (polyacrylonitrile) polymer. A red perovskite LED (PeLED) composite film was fabricated which featured a maximum luminance value of 657 cd/m² at 8 V. We fabricated white PeLEDs by combining hole transporting layer material emission, perovskite–polymer composite material PAN:CsPbBr_2.5I_0.5, and pure inorganic perovskite CsPbBr₃ as a luminescent layer. The maximum luminance of the device was 360 cd/m² at 7 V, and the color coordinate was (0.31, 0.36). We obtained an ideal white light-emitting device that paves the way for further development of white PeLEDs.

High Performance and Stable All-Inorganic Metal Halide Perovskite-Based Photodetectors for Optical Communication Applications

Photodetectors are critical parts of an optical communication system for achieving efficient photoelectronic conversion of signals, and the response speed directly determines the bandwidth of the whole system. Metal halide perovskites, an emerging class of low-cost solution-processed semiconductors, exhibiting strong optical absorption, low trap states, and high carrier mobility, are widely investigated in photodetection applications. Herein, through optimizing the device engineering and film quality, high-performance photodetectors based on all-inorganic cesium lead halide perovskite (CsPbI_x Br_{3- x} ), which simultaneously possess high sensitivity and fast response, are demonstrated. The optimized devices processed from CsPbIBr₂ perovskite show a practically measured detectable limit of about 21.5 pW cm^-2 and a fast response time of 20 ns, which are both among the highest reported device performance of perovskite-based photodetectors. Moreover, the photodetectors exhibit outstanding long-term environmental stability, with negligible degradation of the photoresponse property after 2000 h under ambient conditions. In addition, the resulting perovskite photodetector is successfully integrated into an optical communication system and its applications as an optical signal receiver on transmitting text and audio signals is demonstrated. The results suggest that all-inorganic metal halide perovskite-based photodetectors have great application potential for optical communication.

Spray-Coated CsPbBr3 Quantum Dot Films for Perovskite Photodiodes

Large-area film deposition and high material utilization ratio are the crucial factors for large-scale application of perovskite optoelectronics. Recently, all-inorganic halide perovskite CsPbBr₃ has attracted great attention because of its high phase stability, thermal stability, and photostability. However, most reported perovskite devices were fabricated by spin-coating, suffering from a low material utilization ratio of 1% and a small coverage area. Here, we developed a spray-coating technique to fabricate a CsPbBr₃ quantum dot (QD) film photodiode which had a high material utilization ratio of 32% and a deposition rate of 9 nm/s. The film growth process was studied, and substrate temperature and spray time were two key factors for the deposition of uniform and crack-free QD films. The spray-coated photodiode was demonstrated to be more suitable for working in the photodetector mode because a low dark current density of 4 × 10^-4 mA cm^-2 resulting from an extremely low recombination current contributed to a high detectivity of 1 × 10¹⁴ Jones. A high responsivity of 3 A W^-1 was obtained at -0.7 V under 365 nm illumination, resulting from a low charge-transfer resistance and a high charge recombination resistance. We believe that the spray deposition technique will benefit the fabrication of perovskite QD film optoelectronics on a large scale.

Simplified Perovskite Solar Cell with 4.1% Efficiency Employing Inorganic CsPbBr3 as Light Absorber

Perovskite solar cells with cost-effectiveness, high power conversion efficiency, and improved stability are promising solutions to the energy crisis and environmental pollution. However, a wide-bandgap inorganic-semiconductor electron-transporting layer such as TiO₂ can harvest ultraviolet light to photodegrade perovskite halides, and the high cost of a state-of-the-art hole-transporting layer is an economic burden for commercialization. Here, the building of a simplified cesium lead bromide (CsPbBr₃ ) perovskite solar cell with fluorine-doped tin oxide (FTO)/CsPbBr₃ /carbon architecture by a multistep solution-processed deposition technology is demonstrated, achieving an efficiency as high as 4.1% and improved stability upon interfacial modification by graphene quantum dots and CsPbBrI₂ quantum dots. This work provides new opportunities of building next-generation solar cells with significantly simplified processes and reduced production costs.

High-Performance Red-Light Photodetector Based on Lead-Free Bismuth Halide Perovskite Film

In this study, we developed a sensitive red-light photodetector (RLPD) based on CsBi₃I₁₀ perovskite thin film. This inorganic, lead-free perovskite was fabricated by a simple spin-coating method. Device analysis reveals that the as-assembled RLPD was very sensitive to 650 nm light, with an on/off ratio as high as 10⁵. The responsivity and specific detectivity of the device were estimated to be 21.8 A/W and 1.93 × 10¹³ Jones, respectively, which are much better than those of other lead halide perovskite devices. In addition, the device shows a fast response (rise time: 0.33 ms; fall time: 0.38 ms) and a high external quantum efficiency (4.13 × 10³%). It is also revealed that the RLPD has a very good device stability even after storage for 3 months under ambient conditions. In summary, we suggest that the CsBi₃I₁₀ perovskite photodetector developed in this study may have potential applications in future optoelectronic systems.