21.15%-Efficiency and Stable γ -CsPbI3 Perovskite Solar Cells Enabled by an Acyloin Ligand

Increasing the Phase Stability of CsPbI3 Nanocrystals by Zn2+ and Cd2+ Addition: Synergy of Transmission Electron Microscopy and Molecular Dynamics

Metal halide perovskites (MHPs) are emerging as promising materials for optoelectronic and photovoltaic applications due to their favorable electronic properties, including a tunable bandgap. However, achieving high stability for these materials remains a critical challenge, particularly for CsPbI3, whose photoactive phases spontaneously convert into a nonphotoactive yellow orthorhombic δ-phase under ambient conditions. This transformation results in a significant increase in bandgap and a loss of photoactive functionality. In this study, we investigate the impact of Zn2+ and Cd2+ dopants on the phase stability of CsPbI3 nanocrystals (NCs), emphasizing the formation of Ruddlesden-Popper (RP) planar defects, which are frequently observed during compositional tuning. Using transmission electron microscopy (TEM), we follow the temporal evolution of the phase transformation, where black-phase NCs agglomerate and form elongated microtubes with a yellow-phase crystal structure. Our observations demonstrate that doped samples are significantly more stable, while the dopants are key factors in the formation of the RP-like defects with specific atomic arrangements. Using a combination of quantitative TEM and molecular dynamics (MD) simulations we characterize the structure and composition of as-found RP-like defects and elucidate their role in stabilizing the photoactive phases of CsPbI3 through decreased phase transition kinetics.

Efficient and Super-Stable 990 Nm Light‑Emitting Diodes Based on Quantum Cutting Emission of Trivalent Ytterbium in Pure-Br Quasi‑2D Perovskites

Quasi 2D layered metal halide perovskites (2D-LMHPs) with natural quantum wells (QWs) structure have garnered significant attention due to their excellent optoelectronic properties. Doping rare earth (RE) ions with 4fn inner shell emission levels can largely expand their optical and optoelectronic properties and realize diverse applications, but has not been reported yet. Herein, an efficient Yb3+-doped PEA2Cs2Pb3Br10 quasi 2D-LMHPs is fabricated and directly identified the Yb3+ ions in the quasi 2D-LMHPs at the atomic scale using aberration electron microscopy. The interaction between different n phases and Yb3+ ions is elucidated using ultrafast transient absorption spectroscopy and luminescent dynamics, which demonstrated efficient, different time scales and multi-channel energy transfer processes. Finally, through phase distribution manipulation and surface passivation, the optimized film exhibits a photoluminescence quantum yield of 144%. This is the first demonstration of quantum cutting emission in pure Br-based perovskite material, suppressing defect states and ion migration. The efficient and stable near-infrared light-emitting diodes (NIR LED) is fabricated with a peak external quantum efficiency (EQE) of 8.8% at 990 nm and the record lifetime of 1274 min. This work provides fresh insight into the interaction between RE ions and quasi 2D-LMHPs and extend the function and application of quasi 2D-LMHPs materials.

The Mixed Phases of α and γ-CsPbI₃ Enable Efficient and Stable Semitransparent Solar Cells

Cesium lead iodide (CsPbI₃) is a promising material for semitransparent perovskite solar cells (ST-PSCs) in building-integrated photovoltaics (BIPV) due to its favorable bandgap and thermal stability. However, the phase instability of CsPbI₃ limits its device performance. Developing a simple strategy to regulate the phase transition is essential for enhancing both device efficiency and stability. In this study, synchrotron-based grazing-incidence wide-angle X-ray scattering and in situ X-ray diffraction results revealed that adding HBr promotes the formation of γ-CsPbI₃ at low temperatures. Upon annealing at 100 C, this γ-phase partially converts to α-CsPbI₃, resulting in a mixed-phase film. This mixed-phase film effectively mitigates substrate strain caused by mismatched thermal expansion coefficients and strain generated during phase transitions. Moreover, the mixed-phase CsPbI₃ films exhibit a pinhole-free morphology with reduced defect density, leading to enhanced moisture stability under ≈85% relative humidity. Consequently, the mixed-phase CsPbI₃-based ST-PSC achieved a remarkable power conversion efficiency (PCE) of 19.89% and retained 90.89% of its initial PCE after 500 h of continuous illumination.

Synchronous Perovskite Crystallization Regulation and Buried Interface Modification Improve the Stability and Efficiency of a Planar Inorganic Perovskite Solar Cell

The numerous defects in inorganic perovskites and inferior buried interfaces result in serious nonradiative recombination and energy loss, exacerbating the deterioration of the performance of inorganic perovskite solar cells. Here, we develop a facile strategy to simultaneously improve CsPbIBr2 perovskite quality by regulating perovskite crystallization and modify the buried interface by forming a 6-aminonicotinic acid (6AA) molecular interlayer through adding 6AA into a CsPbIBr2 precursor solution. It is found that adding 6AA into the CsPbIBr2 precursor effectively regulates the crystallization process of CsPbIBr2 perovskite because 6AA molecules exhibit a strong intermolecular interaction with CsPbIBr2 precursor components, resulting in forming a compact CsPbIBr2 perovskite film with improved morphology and decreased defects. Meanwhile, 6AA molecules are pushed downward during the perovskite crystallization process and accumulate at the buried interface to form the 6AA interlayer, which improves the interface contact and enhances the charge transport at the buried interface. The perovskite quality improvement and the buried interface modification effectively decrease the nonradiative recombination and interface charge loss. Consequently, the fabricated planar carbon-based CsPbIBr2 solar cell demonstrates an efficiency of 10.97% with a remarkably promoted long-term stability.

Improved radicchio seedling growth under CsPbI3 perovskite rooftop in a laboratory-scale greenhouse for Agrivoltaics application

Agrivoltaics, integrating photovoltaic systems with crop cultivation, demands semitransparent solar modules to mitigate soil shadowing. Perovskite Solar Cells (PSC) offer competitive efficiency, low fabrication costs, and high solar transmittance, making them suitable for agrivoltaic applications. However, the impact of PSC light filtering on plant growth and transcriptomics remains underexplored. This study investigates the viability and agronomic implications of the growth of radicchio seedlings (Cichorium intybus var. latifolium) in laboratory-scale greenhouses integrating Perovskites-coated rooftops. Eu-enriched CsPbI3 layers are chosen to provide semi-transparency and phase stability while radicchio has limited size and grows in pots. Despite the reduced light exposure, radicchio seedlings exhibit faster growth and larger leaves than in the reference, benefiting from specific spectral filtering. RNA-sequencing reveals differential gene expression patterns reflecting adaptive responses to environmental changes. Simulations of full PSC integration demonstrate a positive energy balance in greenhouses to cover annual energy needs for lighting, irrigation, and air conditioning.

Powering the Future: Opportunities and Obstacles in Lead-Halide Inorganic Perovskite Solar Cells

Efficiency, stability, and cost are crucial considerations in the development of photovoltaic technology for commercialization. Perovskite solar cells (PSCs) are a promising third-generation photovoltaic technology due to their high efficiency and low-cost potential. However, the stability of organohalide perovskites remains a significant challenge. Inorganic perovskites, based on CsPbX₃ (X = Br-/I-), have garnered attention for their excellent thermal stability and optoelectronic properties comparable to those of organohalide perovskites. Nevertheless, the development of inorganic perovskites faces several hurdles, including the need for high-temperature annealing to achieve the photoactive α-phase and their susceptibility to transitioning into the nonphotoactive δ-phase under environmental stressors, particularly moisture. These challenges impede the creation of high-efficiency, high-stability devices using low-cost, scalable manufacturing processes. This review provides a comprehensive background on the fundamental structural, physical, and optoelectronic properties of inorganic lead-halide perovskites. It discusses the latest advancements in fabricating inorganic PSCs at lower temperatures and under ambient conditions. Furthermore, it highlights the progress in state-of-the-art inorganic devices, particularly those manufactured in ambient environments and at reduced temperatures, alongside simultaneous advancements in the upscaling and stability of inorganic PSCs.

Understanding the Decoupled Effects of Cations and Anions Doping for High-Performance Perovskite Solar Cells

The past decade has witnessed the rapid increasement in power conversion efficiency of perovskite solar cells (PSCs). However, serious ion migration hampers their operational stability. Although dopants composed of varied cations and anions are introduced into perovskite to suppress ion migration, the impact of cations or anions is not individually explored, which hinders the evaluation of different cations and further application of doping strategy. Here we report that a special group of sulfonic anions (like CF3SO3-) successfully introduce alkaline earth ions (like Ca2+) into perovskite lattice compared to its halide counterparts. Furthermore, with effective crystallization regulation and defect passivation of sulfonic anions, perovskite with Ca(CF3SO3)2 shows reduced PbI2 residue and metallic Pb0 defects; thereby, corresponding PSCs show an enhanced PCE of 24.95%. Finally by comparing the properties of perovskite with Ca(CF3SO3)2 and FACF3SO3, we found that doped Ca2+ significantly suppressed halide migration with an activation energy of 1.246 eV which accounts for the improved operational stability of Ca(CF3SO3)2-doped PSCs, while no obvious impact of Ca2+on trap density is observed. Combining the benefits of cations and anions, this study presents an effective method to decouple the effects of cations and anions and fabricate efficient and stable PSCs.

Tailoring Buried Interface and Minimizing Energy Loss Enable Efficient Narrow and Wide Bandgap Inverted Perovskite Solar Cells by Aluminum Glycinate Based Organometallic Molecule

Rational regulation of Me-4PACz/perovskite interface has emerged as a significant challenge in the pursuit of highly efficient and stable perovskite solar cells (PSCs). Herein, an organometallic molecule of aluminum glycinate (AG) that contained amine (-NH2) and aluminum hydroxyl (Al-OH) groups is developed to tailor the buried interface and minimize interface-driven energy losses. The Al-OH groups selectively bonded with unanchored O═P-OH and bare NiO-OH to optimize the surface morphology and energy levels, while the -NH2 group interacted specifically with Pb2+ to retard perovskite crystallization, passivate buried Pb-related defects, and release residual interface stress. These interactions facilitate the interface carrier extraction and reduce interface-driven energy losses, thereby realizing a balanced charge carrier transport. Consequently, AG-modified narrow bandgap (1.55 eV) PSC demonstrates an efficiency of 26.74% (certified 26.21%) with a fill factor of 86.65%; AG-modified wide bandgap (1.785 eV) PSC realizes 20.71% champion efficiency with excellent repeatability. These PSCs maintain 91.37%, 91.92%, and 92.00% of their initial efficiency after aging in air atmosphere, the nitrogen-filled atmosphere at 85 °C, and continuously tracking at the maximum power-point under one-sun illumination (100 mW cm-2) for 1200 h, respectively.

The stability of CsGeX3 (X = I, Br, Cl) selectively tuned by the crystal structures and halide ions as inferred from the calculated phonon spectrum

In spite of the considerable advancements achieved in enhancing the power conversion efficiency (PCE) of lead-based all-inorganic perovskite solar cells, there persists a need for materials that are both more stable and environmentally friendly. This investigation systematically explores the structural and thermodynamic stability, and electronic properties of Ge-based all-inorganic perovskite CsGeX3 (X = Cl, Br, I) in two space groups, Pm3̄m and R3m, utilizing first-principles calculations. Introducing the novel concept of the "imaginary frequency coefficient" alongside the tolerance factor and stabilizing the chemical potential window, we collectively characterize the stability of CsGeX3 based on the phonon spectrum and phonon density of states calculations. The findings reveal that the stable phase of the Ge-based perovskite differs from that of lead-based systems, with the R3m structure of CsGeX3 being the most stable in the rhombohedral phase. Moreover, the stability of R3m-CsGeX3 can be manipulated by adjusting the halide composition with a gradual increase in stability observed as halogen atoms shift from I to Cl. This comprehensive approach, integrating the phonon spectrum, innovative measurement indicators, and tolerance factor, presents an effective strategy for designing materials that are both non-toxic and stable.

Crown Ether-Modified 1D/3D Heterojunction for Efficient and Stable Carbon-Based CsPbI3 Perovskite Solar Cells

Interface engineering strategies passivate defects on the polycrystalline perovskite film surface and improve the stability of corresponding perovskite solar cells (PSCs). However, a single interface engineering step can result in restricted benefits on various occasions. Therefore, an appropriate additional modification step can be necessary to synergistically improve the device performance. In this study, a two-step interface engineering strategy is developed. Initially, the CsPbI3 perovskite surface is modified by choline iodide (ChI) to construct a 1D ChPbI3/3D CsPbI3 heterojunction, and then an additional surface modification step with the use of crown ether is applied. The crown ether modification can further eliminate unpassivated surface defects after heterojunction construction. Benefiting from the inhibited interfacial recombination, the resultant carbon-electrode-based CsPbI3 PSCs (C-PSCs) deliver a champion efficiency of 18.78%, representing one of the highest levels in this field. Besides, crown ether can synergistically improve the stability of the device against moisture, heat, and light stress due to the enhanced hydrophobicity and suppressed ion migration.

25.71 %-Efficiency FACsPbI3 Perovskite Solar Cells Enabled by A Thiourea-based Isomer

Various isomers have been developed to regulate the morphology and reduce defects in state-of-the-art perovskite solar cells (PSCs). To insight the structure-function-effect correlations for the isomerization of thiourea derivatives on the performance of the PSCs, we developed two thiourea derivatives [(3,5-dichlorophenyl)amino]thiourea (AT) and N-(3,5-dichlorophenyl)hydrazinecarbothioamide (HB). Supported by experimental and calculated results, it was found that AT can bind with undercoordinated Pb2+ defect through synergistic interaction between N1 and C=S group with a defect formation energy of 1.818 eV, which is much higher than that from the synergistic interaction between two -NH- groups in HB and perovskite (1.015 eV). Moreover, the stronger interaction between AT and Pb2+ regulates the crystallization process of perovskite film to obtain a high-quality perovskite film with high crystallinity, large grain size, and low defect density. Consequently, the AT-treated FACsPbI3 device engenders an efficiency of 25.71 % (certified as 24.66 %), which is greatly higher than control (23.74 %) and HB-treated FACsPbI3 devices (25.05 %). The resultant device exhibits a remarkable stability for maintaining 91.0 % and 95.2 % of its initial efficiency after aging 2000 h in air condition or tracking at maximum power point for 1000 h, respectively.

High Open-Circuit Voltage Wide-Bandgap Perovskite Solar Cell with Interface Dipole Layer

Wide-bandgap perovskite solar cells (PSCs) with high open-circuit voltage (Voc) represent a compelling and emerging technological advancement in high-performing perovskite-based tandem solar cells. Interfacial engineering is an effective strategy to enhance Voc in PSCs by tailoring the energy level alignments between the constituent layers. Herein, n-type quinoxaline-phosphine oxide-based small molecules with strong dipole moments is designed and introduce them as effective cathode interfacial layers. Their strong dipole effect leads to appropriate energy level alignment by tuning the work function of the Ag electrode to form an ohmic contact and enhance the built-in potential within the device, thereby improving charge-carrier transport and mitigating charge recombination. The organic interfacial layer-modified wide-bandgap PSCs exhibit a high Voc of 1.31 V (deficit of <0.44 V) and a power conversion efficiency (PCE) of 20.3%, significantly improved from the device without an interface dipole layer (Voc of 1.26 V and PCE of 16.7%). Furthermore, the hydrophobic characteristics of the small molecules contribute to improved device stability, retaining 95% of the initial PCE after 500 h in ambient air.

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.

Regulation of the Buried Interface to Achieve Efficient HTL-Free All-Inorganic CsPbI2Br-Based Perovskite Solar Cells

The large voltage loss (Vloss) mainly stems from the mismatch between the perovskite film and electron transport layer in CsPbI2Br-based all-inorganic perovskite solar cells (I-PSCs), which restricts the power conversion efficiency (PCE) of devices. To address this issue, potassium benzoate (BAP) is first introduced as a bifunctional passivation material to regulate the TiO2/CsPbI2Br interface, reduce the Vloss, and improve the photovoltaic performance of CsPbI2Br-based I-PSCs. Eventually, the champion PCE of CsPbI2Br-based I-PSCs without a hole transport layer modified by BAP (Target-PSCs) improves to 14.90% from the 12.14% of reference PSCs. The open-circuit voltage (Voc) increases to 1.27 V from the initial 1.14 V after BAP modification. A series of characterizations show that BAP modification can not only optimize the energy level alignment of I-PSCs but also passivize the surface defects caused by uncoordinated Cs+/Pb2+. Moreover, the Target-PSCs without encapsulation demonstrate better thermal stability, which can maintain 107.6% of the original PCE after annealing at 160 °C for 140 min in humid air. While the reference PSCs only maintain 76.5% of their initial PCE after annealing at the same process. This work provides a simple strategy to modify the buried interface and improve the performance of CsPbI2Br-based I-PSCs.

Performance Enhancement of Hole Transport Layer-Free Carbon-Based CsPbIBr2 Solar Cells through the Application of Perovskite Quantum Dots

CsPbIBr2, with its suitable bandgap, shows great potential as the top cell in tandem solar cells. Nonetheless, its further development is hindered by a high defect density, severe carrier recombination, and poor stability. In this study, CsPbI1.5Br1.5 quantum dots were utilized as an additive in the ethyl acetate anti-solvent, while a layer of CsPbBr3 QDs was introduced between the ETL and the CsPbIBr2 light-harvester film. The combined effect of these two QDs enhanced the nucleation, crystallization, and growth of CsPbIBr2 perovskite, yielding high-quality films characterized by an enlarged crystal size, reduced grain boundaries, and smooth surfaces. And a wider absorption range and better energy band alignment were achieved owing to the nano-size effect of QDs. These improvements led to a decreased defect density and the suppression of non-radiative recombination. Additionally, the presence of long-chain organic molecules in the QD solution promoted the formation of a hydrophobic surface, significantly enhancing the long-term stability of CsPbIBr2 PSCs. Consequently, the devices achieved a PCE of 9.20% and maintained an initial efficiency of 85% after 60 days of storage in air. Thus, this strategy proves to be an effective approach for the preparation of efficient and stable CsPbIBr2 PSCs.

Structural and excitonic properties of the polycrystalline FAPbI3thin films, and their photovoltaic responses

Faormamadinium based perovskites have been proposed to replace the methylammonium lead tri-iodide (MAPbI3) perovskite as the light absorbing layer of photovoltaic cells owing to their photo-active and chemically stable properties. However, the crystal phase transition from the photo-activeα-FAPbI3to the non-perovksiteδ-FAPbI3still occurs in un-doped FAPbI3films owing to the existence of crack defects, which degrads the photovoltaic responses. To investigate the crack ratio (CR)-dependent structure and excitonic characteristics of the polycrystalline FAPbI3thin films deposited on the carboxylic acid functionalized ITO/glass substrates, various spectra and images were measured and analyzed, which can be utilized to make sense of the different devices responses of the resultant perovskite based photovoltaic cells. Our experimental results show that the there is a trade-off between the formations of surface defects and trapped iodide-mediated defects, thereby resulting in an optimal crack density or CR of the un-dopedα-FAPbI3active layer in the range from 4.86% to 9.27%. The decrease in the CR (tensile stress) results in the compressive lattice and thereby trapping the iodides near the PbI6octahedra in the bottom region of the FAPbI3perovskite films. When the CR of the FAPbI3film is 8.47%, the open-circuit voltage (short-circuit current density) of the resultant photovoltaic cells significantly increased from 0.773 V (16.62 mA cm-2) to 0.945 V (18.20 mA cm-2) after 3 d. Our findings help understanding the photovoltaic responses of the FAPbI3perovskite based photovoltaic cells on the different days.

Eliminating Hole Extraction Barrier in 1D/3D Perovskite Heterojunction for Efficient and Stable Carbon-Based CsPbI3 Solar Cells with a Record Efficiency

Carbon-based perovskite solar cells (C-PSCs) have the advantages of low-cost and high-stability, but their photovoltaic performance is limited by severe defect-induced recombination and low hole extraction efficiency. 1D perovskite is proven to effectively passivate the defects on the perovskite surface, therefore reducing non-radiative recombination loss. However, the unsuitable energy level of most 1D perovskite renders an undesired downward band bending for 3D perovskite, resulting in a high hole extraction barrier and reduced hole extraction efficiency. Therefore, rational design and selection of 1D perovskites as the modifiers are essential in balancing defect passivation and hole extraction. In this work, based on simulation calculations, thiocholine iodide (TchI) is selected to prepare 1D perovskite with high work function and then constructs TchPbI3/CsPbI3 1D/3D perovskite heterojunction. Experimental results show that this strategy eliminates the hole extraction barrier at the perovskite/carbon interface, which improves the hole extraction efficiency of corresponding devices. Meanwhile, the strong interaction between the thiol group and Pb suppresses defect-induced recombination effectively and improves the stability of CsPbI3. The assembled C-PSCs exhibit a champion efficiency of 19.08% and a certified efficiency of 18.7%. To the best of the knowledge, this is a new efficiency record for inorganic C-PSCs.

Stability Strategies and Applications of Iodide Perovskites

Iodide perovskites have demonstrated their unprecedented high efficiency and commercialization potential, and their superior optoelectronic properties, such as high absorption coefficient, high carrier mobility, and narrow direct bandgap, have attracted much attention, especially in solar cells, photodetectors, and light-emitting diodes (LEDs). However, whether it is organic iodide perovskite, organic-inorganic hybrid iodide perovskite or all-inorganic iodide perovskite the stability of these iodide perovskites is still poor and the contamination is high. In recent years, scholars have studied more iodide perovskites to improve their stability as well as optoelectronic properties from various angles. This paper systematically reviews the strategies (component engineering, additive engineering, dimensionality reduction engineering, and phase mixing engineering) used to improve the stability of iodide perovskites and their applications in recent years.

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.

Phase stabilization of cesium lead iodide perovskites for use in efficient optoelectronic devices

All-inorganic lead halide perovskites (LHPs) and their use in optoelectronic devices have been widely explored because they are more thermally stable than their hybrid organic‒inorganic counterparts. However, the active perovskite phases of some inorganic LHPs are metastable at room temperature due to the critical structural tolerance factor. For example, black phase CsPbI3 is easily transformed back to the nonperovskite yellow phase at ambient temperature. Much attention has been paid to improving the phase stabilities of inorganic LHPs, especially those with high solar cell efficiencies. Herein, we discussed the origin of phase stability for CsPbI3 and the strategies used to stabilize the cubic (α) phase. We also assessed the CsPbI3 black β/γ phases that are relatively stable at nearly room temperature. Furthermore, we determined the relationship between phase stabilization and defect passivation and reviewed the growing trend in solar cell efficiency based on black phase CsPbI3. Finally, we provide perspectives for future research related to the quest for optimum device efficiency and green energy.

Antisolvent-Free Heterogenous Nucleation Enabled by Employing 4-Tert-Butyl Pyridine Additive and Two-Step Annealing for Efficient CsPbI2Br Perovskite Solar Cells

All inorganic perovskite based on CsPbI2Br has attracted significant attention due to its relatively thermal stable structure compare to its hybrid counterparts. With a wide bandgap of 1.9 eV and excellent light absorption capability, it has been extensively explored for applications in indoor photovoltaics and as a front absorber in tandem devices. However, the uncontrollable crystallization process during solvent evaporation and thermal annealing leads to both macroscopic defects like cracks and microscopic defects such as voids. In this study, a metastable adduct with lead (II) halides by incorporating 4-tert-butyl pyridine as a volatile Lewis base monodentate ligand in the precursor solution is formed. The strategic preferential decomposition of the adduct during the early-stage low-temperature annealing facilitated the desorption of lead (II) halides, inducing antisolvent-free heterogenous nucleation. This, in turn, promoted crystal growth during subsequent high-temperature annealing, resulting in dense films with low defect density. As a result, a maximum open-circuit voltage of 1.30 V is achieved with the champion power conversion efficiency of 16.5% in CsPbI2Br-based perovskite solar cell. The work reveals a new mechanism of using Lewis acid-base adduct to obtain high quality perovskite films other than hindering crystallization in traditional way.

Photochemical Shield Enabling Highly Efficient Perovskite Photovoltaics

Oxygen is difficult to be physically removed. Oxygen will be excited by light to form free radicals which further attack the lattice of perovskite. The stabilization of α-FAPbI3 against δ-FAPbI3 is the key to optimize perovskite solar cells. Herein, the simple molecule, benzaldehyde (BAH) is adopted. The photochemical shield will be established in perovskite layer. Moreover, heterogeneous nucleation induced by BAH enhances the crystallization of α-FAPbI3. Consequently, the stability of device is improved significantly. The target device maintains 95% of original power conversion efficiency after 1500 h under air conditions and light-emitting diode light. The power conversion efficiency increases from 23.21% of pristine device to 24.82% of target device.

Improvement of Thermal Stability and Photoelectric Performance of Cs2PbI2Cl2/CsPbI2.5Br0.5 Perovskite Solar Cells by Triple-Layer Inorganic Hole Transport Materials

Conventional hole transport layer (HTL) Spiro-OMeTAD requires the addition of hygroscopic dopants due to its low conductivity and hole mobility, resulting in a high preparation cost and poor device stability. Cuprous thiocyanate (CuSCN) is a cost-effective alternative with a suitable energy structure and high hole mobility. However, CuSCN-based perovskite solar cells (PSCs) are affected by environmental factors, and the solvents of an HTL can potentially corrode the perovskite layer. In this study, a Co3O4/CuSCN/Co3O4 sandwich structure was proposed as an HTL for inorganic Cs2PbI2Cl2/CsPbI2.5Br0.5 PSCs to address these issues. The Co3O4 layers can serve as buffer and encapsulation layers, protecting the perovskite layer from solvent-induced corrosion and enhancing hole mobility at the interface. Based on this sandwich structure, the photovoltaic performances of the Cs2PbI2Cl2/CsPbI2.5Br0.5 PSCs are significantly improved, with the power conversion efficiency (PCE) increasing from 9.87% (without Co3O4) to 11.06%. Furthermore, the thermal stability of the devices is also significantly enhanced, retaining 80% of its initial PCE after 40 h of continuous aging at 60 °C. These results indicate that the Co3O4/CuSCN/Co3O4 sandwich structure can effectively mitigate the corrosion of the perovskite layer by solvents of an HTL and significantly improves the photovoltaic performance and thermal stability of devices.

Multifunctional Biomolecules Bridging a Buried Interface for Efficient Perovskite Solar Cells

The inevitably positively and negatively charged defects on the SnO2/perovskite buried interface often lead to nonradiative recombination of carriers and unfavorable alignment of energy levels in perovskite solar cells (PSCs). Interface engineering is a reliable strategy to manage charged defects. Herein, the nicotinamide adenine dinucleotide (NAD) molecules with multiple active groups of ─P=O, ─P-O, and ─NH2 are introduced to bridge the SnO2/perovskite buried interface for achieving simultaneous elimination of positively and negatively charged defects. We demonstrate that the ─P=O and ─P-O groups in NAD not only fix the uncoordinated Pb2+ but also fill the oxygen vacancies (VO) on the SnO2 layer to eliminate positively charged defects. Meanwhile, ─NH2 groups form hydrogen bonds with PbI2 to reduce the number of negatively charged defects. In addition, the NAD biomolecules as a bridge induce high perovskite crystallization and accelerated electronic transfer along with favorable energy band alignment between SnO2 and perovskite. Finally, the PSCs with the ITO/SnO2/NAD/Cs0.15FA0.75MA0.1PbI3/Spiro-OMeTAD/Ag structure deliver an improvement in the power conversion efficiency from 20.49 to 23.18% with an excellent open-circuit voltage (Voc) of 1.175 V. This work demonstrates that interface engineering through multifunctional molecular bridges with various functional groups is an effective approach to improve the performance of PSCs by eliminating charged defects and simultaneously regulating energy level alignment.

Ionic Liquid Bridge Assisting Bifacial Defect Passivation for Efficient All-Inorganic Perovskite Cells with High Open-Circuit Voltage

Serious open-circuit voltage (Voc) loss originating from nonradiative recombination and mismatch energy level at TiO2/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) perovskite solar cells (PSCs) fabricated through low-temperature methods. Here, an ionic liquid (IL) bridge is constructed by introducing 1-butyl-3-methylimidazolium acetate (BMIMAc) IL to treat the TiO2/perovskite buried interface, bilaterally passivate defects and modulate energy alignment. Therefore, the Voc of all-inorganic CsPbIBr2 PSCs modified by BMIMAc (Target-1) significantly increases by 148 mV (from 1.213 to 1.361 V), resulting in the efficiency increasing to 10.30% from 7.87%. Unsealed Target-1 PSCs show outstanding long-term and thermal stability. During the accelerated degradation process (85 °C, RH: 50∼60%), the Target-1 PSCs achieve a champion PCE of 11.94% with a remarkable Voc of 1.403 V, while the control PSC yields a promising PCE of 10.18% with a Voc of 1.319 V. In particular, the Voc of 1.403 V is the highest Voc reported so far in carbon-electrode-based CsPbIBr2 PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI2Br PSCs to achieve a Voc of 1.295 V and a champion efficiency of 15.20%, which is close to the reported highest PCE of 15.48% for all-inorganic CsPbI2Br PSCs prepared by a low-temperature process. This study provides a simple BMIMAc IL bridge to assist bifacial defect passivation and elevate the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) PSCs.

Cesium Cyclopropane Acid-Aided Crystal Growth Enables Efficient Inorganic Perovskite Solar Cells with a High Moisture Tolerance

While all-inorganic halide perovskites (iHPs) are promising photovoltaic materials, the associated water sensitivity of iHPs calls for stringent humidity control to reach satisfactory photovoltaic efficiencies. Herein, we report a moisture-insensitive perovskite formation route under ambient air for CsPbI2 Br-based iHPs via cesium cyclopropane acids (C3 ) as a compound introducer. With this approach, appreciably enhanced crystallization quality and moisture tolerance of CsPbI2 Br are attained. The improvements are attributed to the modified evaporation enthalpy of the volatile side product of DMA-acid initiated by Cs-acids. As such, the water-involving reaction is directed toward the DMA-acids, leaving the target CsPbI2 Br perovskites insensitive to ambient humidity. We highlight that by controlling the C3 concentration, the dependence of power conversion efficiency (PCE) in CsPbI2 Br devices on the humidity level during perovskite film formation becomes favorably weakened, with the PCEs remaining relatively high (>15 %) associated with improved device stability for RH levels changed from 25 % to 65 %. The champion solar cells yield an impressive PCE exceeding 17 %, showing small degradations (<10 %) for 2000 hours of shell storage and 300 hours of 85/85 (temperature/humidity) tests. The demonstrated C3 -based strategy provides an enabler for improving the long-sought moisture-stability of iHPs toward high photovoltaic device performance.

Eco-Friendly Solvent Engineered CsPbI2.77 Br0.23 Ink for Large-Area and Scalable High Performance Perovskite Solar Cells

The performance of large-area perovskite solar cells (PSCs) has been assessed for typical compositions, such as methylammonium lead iodide (MAPbI3 ), using a blade coater, slot-die coater, solution shearing, ink-jet printing, and thermal evaporation. However, the fabrication of large-area all-inorganic perovskite films is not well developed. This study develops, for the first time, an eco-friendly solvent engineered all-inorganic perovskite ink of dimethyl sulfoxide (DMSO) as a main solvent with the addition of acetonitrile (ACN), 2-methoxyethanol (2-ME), or a mixture of ACN and 2-ME to fabricate large-area CsPbI2.77 Br0.23 films with slot-die coater at low temperatures (40-50 °C). The perovskite phase, morphology, defect density, and optoelectrical properties of prepared with different solvent ratios are thoroughly examined and they are correlated with their respective colloidal size distribution and solar cell performance. The optimized slot-die-coated CsPbI2.77 Br0.23 perovskite film, which is prepared from the eco-friendly binary solvents dimethyl sulfoxide:acetonitrile (0.8:0.2 v/v), demonstrates an impressive power conversion efficiency (PCE) of 19.05%. Moreover, the device maintains ≈91% of its original PCE after 1 month at 20% relative humidity in the dark. It is believed that this study will accelerate the reliable manufacturing of perovskite devices.

Managing Interfacial Charged Defects with Multiple Active Sited Macrocyclic Valinomycin for Efficient and Stable Inverted Perovskite Solar Cells

The unavoidably positively and negatively charged defects at the interface between perovskite and electron transport layer (ETL) often lead to severe surface recombination and unfavorable energy level alignment in inverted perovskite solar cells (PerSCs). Inserting interlayers at this interface is an effective approach to eliminate charged defects. Herein, the macrocyclic molecule valinomycin (VM) with multiple active sites of ─C═O, ─NH, and ─O─ is employed as an interlayer at the perovskite/ETL contact to simultaneously eliminate positively and negatively charged defects. Combined with a series of theoretical calculations and experimental analyzes, it is demonstrated that the ─C═O and ─O─ groups in VM can immobilize the uncoordinated Pb2+ to manage the positively charged defect and the formation of N─H···I hydrogen bonding can recompense the formamidine vacancies to eliminate the negatively charged defect. In addition, the VM interlayer induces a favorable downshift band bending at the perovskite/ETL interface, facilitating charge separation and boosting charge transfer. Thanks to the reduced charged defects and favorable energy level alignment, the fabricated inverted PerSC delivers an outstanding power conversion efficiency of 24.06% with excellent long-term ambient and thermal stability. This work demonstrates that managing charged defects via multiple functional groups and simultaneously regulating energy level alignment is a reliable strategy to boost the performance of PerSCs.

Humidifying, heating and trap-density effects on triple-cation perovskite solar cells

The effect of moisture and heat are important challenges in perovskite solar cells (PSCs). Herein we studied the performance of triple-cation PSCs in different operating environmental conditions. Humidified cells exhibited a hopeful character by increasing the open-circuit voltage (VOC) and short-circuit current density (JSC) to 940 mV and 22.85 mA cm-2 with a power conversion efficiency (PCE) of 14.34%. In addition, further analyses showed that hysteresis index and charge transfer resistance decrease down to 0.4% and 1.67 kΩ. The origin of superior stability is ion segregation to the interface, which removes the antisite defect states. Finally, the effect of operating temperature and trap density on structure and performance was also studied systematically.

Phase Behavior and Role of Organic Additives for Self-Doped CsPbI3 Perovskite Semiconductor Thin Films

The phase change of all-inorganic cesium lead halide (CsPbI3) thin film from yellow δ-phase to black γ-/α-phase has been a topic of interest in the perovskite optoelectronics field. Here, the main focus is how to secure a black perovskite phase by avoiding a yellow one. In this work, we fabricated a self-doped CsPbI3 thin film by incorporating an excess cesium iodide (CsI) into the perovskite precursor solution. Then, we studied the effect of organic additive such as 1,8-diiodooctane (DIO), 1-chloronaphthalene (CN), and 1,8-octanedithiol (ODT) on the optical, structural, and morphological properties. Specifically, for elucidating the binary additive-solvent solution thermodynamics, we employed the Flory-Huggins theory based on the oligomer level of additives' molar mass. Resultantly, we found that the miscibility of additive-solvent displaying an upper critical solution temperature (UCST) behavior is in the sequence CN:DMF > ODT:DMF > DIO:DMF, the trends of which could be similarly applied to DMSO. Finally, the self-doping strategy with additive engineering should help fabricate a black γ-phase perovskite although the mixed phases of δ-CsPbI3, γ-CsPbI3, and Cs4PbI6 were observed under ambient conditions. However, the results may provide insight for the stability of metastable γ-phase CsPbI3 at room temperature.

High-Performance Semi-Transparent Perovskite Solar Cells with over 22% Visible Transparency: Pushing the Limit through MXene Interface Engineering

Semi-transparent perovskite solar cells (ST-PSCs) have attracted enormous attention recently due to their potential in building-integrated photovoltaic. To obtain adequate average visible transmittance (AVT), a thin perovskite is commonly employed in ST-PSCs. While the thinner perovskite layer has higher transparency, its light absorption efficiency is reduced, and the device shows lower power conversion efficiency (PCE). In this work, a combination of high-quality transparent conducting layers and surface engineering using 2D-MXene results in a superior PCE. In situ high-temperature X-ray diffraction provides direct evidence that the MXene interlayer retards the perovskite crystallization process and leads to larger perovskite grains with fewer grain boundaries, which are favorable for carrier transport. The interfacial carrier recombination is decreased due to fewer defects in the perovskite. Consequently, the current density of the devices with MXene increased significantly. Also, optimized indium tin oxide provides appreciable transparency and conductivity as the top electrode. The semi-transparent device with a PCE of 14.78% and AVT of over 26.7% (400-800 nm) was successfully obtained, outperforming most reported ST-PSCs. The unencapsulated device maintained 85.58% of its original efficiency after over 1000 h under ambient conditions. This work provides a new strategy to prepare high-efficiency ST-PSCs with remarkable AVT and extended stability.

Research Progress of Green Solvent in CsPbBr3 Perovskite Solar Cells

In optoelectronic applications, all-Brominated inorganic perovskite CsPbBr₃ solar cells have received a great deal of attention because of their remarkable stability and simplicity of production. Most of the solvents used in CsPbBr₃ perovskite solar cells are toxic, which primarily hinders the commercialization of the products. In this review, we introduce the crystal structure and fundamental properties of CsPbBr₃ materials and the device structure of perovskite cells, summarize the research progress of green solvents for CsPbBr₃ PSCs in recent years from mono-green solvent systems to all-green solvent systems, and discuss the approaches to improving the PCE of CsPbBr₃ PSCs, intending to facilitate the sustainable development of CsPbBr₃ perovskite solar cells. Finally, we survey the future of green solvents in the area of CsPbBr₃ perovskite solar cells.