Fluorine-Containing Passivation Layer via Surface Chelation for Inorganic Perovskite Solar Cells

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI_3−xBr_x film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35 % and 17.21 % for 0.09 cm² and 1.0 cm² device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78 % under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93 % of the initial PCE after 960 h.     

Aggregation-induced Emission Materials for High-efficiency Perovskite Solar Cells

The perovskite solar cells (PSCs) with high efficiency and stability are in great demand for commercial applications. Although the remarkable photovoltaic feature of perovskite layer plays a great role in improving the PCE of PSCs, the inevitable defects and poor stability of perovskite, etc. are the bottleneck and restrict the commercialization of PSCs. Herein, a review provides a strategy of applying aggregation-induced emission (AIE) molecules, containing passivation functional groups and distinct AIE character, which serves as the alternative materials for fabricating high-efficiency and high-stability PSCs. The methods of introducing AIE molecules to PSCs are also summarized, including additive engineering, interfacial engineering, hole transport materials and so on. In addition, the functions of AIE molecule are discussed, such as defects passivation, morphology modulation, well-matched energy level, enhanced stability, hole transport ability, carrier recombination suppression. Finally, the detailed functions of AIE molecules are offered and further research trend for high performance PSCs based on AIE materials is proposed.     

Dual-Interface Engineering in Perovskite Solar Cells with 2D Carbides

Passivating the interfaces between the perovskite and charge transport layers is crucial for enhancing the power conversion efficiency (PCE) and stability in perovskite solar cells (PSCs). Here we report a dual-interface engineering approach to improving the performance of FA_0.85MA_0.15Pb(I_0.95Br_0.05)₃-based PSCs by incorporating Ti₃C₂Cl_x Nano-MXene and o-TB-GDY nanographdiyne (NanoGDY) into the electron transport layer (ETL)/perovskite and perovskite/ hole transport layer (HTL) interfaces, respectively. The dual-interface passivation simultaneously suppresses non-radiative recombination and promotes carrier extraction by forming the Pb−Cl chemical bond and strong coordination of π-electron conjugation with undercoordinated Pb defects. The resulting perovskite film has an ultralong carrier lifetime exceeding 10 μs and an enlarged crystal size exceeding 2.5 μm. A maximum PCE of 24.86 % is realized, with an open-circuit voltage of 1.20 V. Unencapsulated cells retain 92 % of their initial efficiency after 1464 hours in ambient air and 80 % after 1002 hours of thermal stability test at 85 °C.     

Managing Excess Lead Iodide with Functionalized Oxo-Graphene Nanosheets for Stable Perovskite Solar Cells

Stability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI₂) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo-graphene nanosheets (Dec-oxoG NSs) to effectively manage the excess PbI₂. Dec-oxoG NSs provide anchoring sites to bind the excess PbI₂ and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec-oxoG NSs leads to a PCE of 23.7 % in inverted (p-i-n) PSCs. The devices retain 93.8 % of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one-sun illumination and exhibit high stability under thermal and ambient conditions.     

Tetra‐ammonium Zinc Phthalocyanine to Construct a Graded 2D–3D Perovskite Interface for Efficient and Stable Solar Cells

The crystallographic defects inevitably incur during the solution processed organic‐inorganic hybrid perovskite film, especially at surface and the grain boundaries (GBs) of perovskite film, which can further result in the reduced cell performance and stability of perovskite solar cells (PSCs). Here, a simple defect passivation method was employed by treating perovskite precursor film with a hydrophobic tetra‐ammonium zinc phthalocyanine (ZnPc). The results demonstrated that a 2D‐3D graded perovskite interface with a capping layer of 2D (ZnPc)_0.5MA_n ? 1Pb_nI_3n + 1 perovskite together with 3D MAPbI₃ perovskite was successfully constructed on the top of 3D perovskite layer. This situation realized the efficient GBs passivation, thus reducing the defects in GBs. As expected, the corresponding PSCs with modified perovskite revealed an improved cell performance. The best efficiency reached 19.6%. Especially, the significantly enhanced long‐term stability of the responding PSCs against humidity and heating was remarkably achieved. Such a strategy in this work affords an efficient method to improve the stability of PSCs and thus probably brings the PSCs closer to practical commercialization.     

A Multifunctional Polymer as an Interfacial Layer for Efficient and Stable Perovskite Solar Cells

Metal-cation defects and halogen-anion defects in perovskite films are critical to the efficiency and stability of perovskite solar cells (PSCs). In this work, a random polymer, poly(methyl methacrylate-co-acrylamide) (PMMA-AM), was synthesized to serve as an interfacial passivation layer for synergistically passivating the under-coordinated Pb²⁺ and anchor the I^- of the [PbI₆]⁴⁻ octahedron. Additionally, the interfacial PMMA-AM passivation layer cannot be destroyed during the hole transport layer deposition because of its low solubility in chlorobenzene. This passivation leads to an enhancement in the open-circuit voltage from 1.12 to 1.22 V and improved stability in solar cell devices, with the device maintaining 95 % of the initial power conversion efficiency (PCE) over 1000 h of maximum power point tracking. Additionally, a large-area solar cell module was fabricated using this approach, achieving a PCE of 20.64 %.     

Defect and doping concentration study with series and shunt resistance influence on graphene modified perovskite solar cell: A numerical investigation in SCAPS-1D framework

Perovskite solar cells (PSCs) have the potential to be highly efficient, low-cost next-generation solar cells. By raising open circuit voltage (V_oc), the interfacial recombination kinetics can further improve device performance. In this study, we used simulation concept to elucidate the influence of using graphene as a surface passivation material in perovskite solar cells. Graphene works well as an interlayer to promote hole extraction and reduce interfacial recombination. In order to evaluate the effect of graphene in PSCs, the simulation was done in the SCAPS-1D framework to compare the performance of a device with and without graphene. Three interface layers were included to the model: TiO₂/MAPbI₃, MAPbI₃/Graphene, and Graphene/Spiro-OMeTAD, in order to account for the impacts of interface defect density on device performance. The impacts of absorber doping concentration, absorber defect density, ETL doping concentration, HTL doping concentration, series resistance, and shunt resistance were also evaluated for the modelled PSC. Without any optimization, the control device with power conversion efficiency (PCE) of 20.677% was outperformed by the graphene-modified device with PCE of 20.911%. This difference is mostly due to the lower recombination losses and more effective suppression of interfacial non-radiative recombination. With optimization, the modified graphene-based device has a PCE of 26.667%. This result shows an enhancement of ∼1.28 times over that of the pristine graphene-based device. The outcomes have opened the way for the development of cost-effective and comparable state-of-the-art, high-efficiency perovskite solar cells with graphene interlayer by eliminating defects and managing non-radiative recombination.     

Low temperature fabrication for high-performance semitransparent CsPbI2Br perovskite solar cells

All-inorganic Cs Pb I₂Br perovskite with suitable bandgap and excellent thermal stability has been reported as the most promising candidate for efficient perovskite solar cells（PSCs）. However, the high annealing temperature（> 250 °C） and poor stability of α-Cs Pb I₂Br greatly limit the future application in photovoltaic field. Herein, a facile method is reported to prepare α-Cs Pb I₂Br perovskite film with high stability at low temperature（70 °C） by incorporat...     

Low-Cost Hydroxyacid Potassium Synergists as an Efficient In Situ Defect Passivator for High Performance Tin-Oxide-Based Perovskite Solar Cells

Perovskite solar cells (PSCs) based on SnO₂ electron transport layers have attracted extensive research due to their compelling photovoltaic performance. Herein, we presented an in situ passivation of SnO₂ with low-cost hydroxyacid potassium synergist during deposition to optimize the interface carrier extraction and transport for high power conversion efficiency (PCE) and stabilities of PSCs. The orbital overlap of the carboxyl oxygen with the Sn atom alongwith the homogenous nano-particle deposition effectively suppresses the interfacial defects and releases the internal residual strains in the perovskite. Accordingly, a PCE of 24.91 % with a fill factor (FF) up to 0.852 is obtained for in situ passivated devices, which is one of the highest values for SnO₂-based PSCs. Moreover, the unencapsulated device maintained 80 % of its initial PCE at 80 °C over 600 h, 100 % PCE at ambient conditions for 1300 h, and 98 % after one week maximum power point tracking (MPPT) under continuous AM1.5G illumination.     

1D Choline-PbI3-Based Heterostructure Boosts Efficiency and Stability of CsPbI3 Perovskite Solar Cells

Defects in perovskite are key factors in limiting the photovoltaic performance and stability of perovskite solar cells (PSCs). Generally, choline halide (ChX) can effectively passivate defects by binding with charged point defects of perovskite. However, we verified that ChI can react with CsPbI₃ to form a novel crystal phase of one-dimensional (1D) ChPbI₃, which constructs 1D/3D heterostructure with 3D CsPbI₃, passivating the defects of CsPbI₃ more effectively and then resulting in significantly improved photoluminescence lifetime from 20.2 ns to 49.4 ns. Moreover, the outstanding chemical inertness of 1D ChPbI₃ and the repair of undesired δ-CsPbI₃ deficiency during its formation process can significantly enhance the stability of CsPbI₃ film. Benefiting from 1D/3D heterostructure, CsPbI₃ carbon-based PSCs (C-PSCs) delivered a champion efficiency of 18.05 % and a new certified record of 17.8 % in hole transport material (HTM)-free inorganic C-PSCs.     

Designing a Perylene Diimide/Fullerene Hybrid as Effective Electron Transporting Material in Inverted Perovskite Solar Cells with Enhanced Efficiency and Stability

Electron transport materials (ETM) play an important role in the improvement of efficiency and stability for inverted perovskite solar cells (PSCs). This work reports an efficient ETM, named PDI‐C₆₀, by the combination of perylene diimide (PDI) and fullerene. Compared to the traditional PCBM, this strategy endows PDI‐C₆₀ with slightly shallower energy level and higher electron mobility. As a result, the device based on PDI‐C₆₀ as electron transport layer (ETL) achieves high power conversion efficiency (PCE) of 18.6 %, which is significantly higher than those of the control devices of PCBM (16.6 %) and PDI (13.8 %). The high PCE of the PDI‐C₆₀‐based device can be attributed to the more matching energy level with the perovskite, more efficient charge extraction, transport, and reduced recombination rate. To the best of our knowledge, the PCE of 18.6 % is the highest value in the PSCs using PDI derivatives as ETLs. Moreover, the device with PDI‐C₆₀ as ETL exhibits better device stability due to the stronger hydrophobic properties of PDI‐C₆₀. The strategy using the PDI/fullerene hybrid provides insights for future molecular design of the efficient ETM for the inverted PSCs.     

Manipulation of the Buried Interface for Robust Formamidinium-based Sn−Pb Perovskite Solar Cells with NiOx Hole-Transport Layers

Low band gap tin-lead perovskite solar cells (Sn−Pb PSCs) are expected to achieve higher efficiencies than Pb-PSCs and regarded as key components of tandem PSCs. However, the realization of high efficiency is challenged by the instability of Sn²⁺ and the imperfections at the charge transfer interfaces. Here, we demonstrate an efficient ideal band gap formamidinium (FA)-based Sn−Pb (FAPb_0.5Sn_0.5I₃) PSC, by manipulating the buried NiO_x/perovskite interface with 4-hydroxyphenethyl ammonium halide (OH-PEAX, X=Cl⁻, Br⁻, or I⁻) interlayer, which exhibits fascinating functions of reducing the surface defects of the NiO_x hole transport layer (HTL), enhancing the perovskite film quality, and improving both the energy level matching and physical contact at the interface. The effects of different halide anions have been elaborated and a 20.53 % efficiency is obtained with OH-PEABr, which is the highest one for FA-based Sn−Pb PSCs using NiO_x HTLs. Moreover, the device stability is also boosted.     

Electron Acceptor Molecule Doping Induced π–π Interaction to Promote Charge Transport Kinetics for Efficient and Stable 2D/3D Perovskite Solar Cells

Although the incorporation of 2D perovskite into 3D perovskite can greatly enhance intrinsic stability, power conversion efficiency (PCE) of 2D/3D perovskite is still inferior to its 3D counterpart due to poor carrier transport kinetics resulted from the quantum and dielectric confinement of 2D component. To overcome this issue, the electron acceptor molecule 1,2,4,5-tetracyanobenzene (TCNB) was introduced to trigger intermolecular π–π interaction in 2D perovskite along with the electronic doping of 2D/3D perovskite to improve charge transfer efficiency. By virtue of high electron affinity, TCNB can undergo electron transfer reaction and subsequently establish π–π interaction with 1-naphthalenemethylammonium (NMA) cations, greatly strengthening lattice rigidity and reducing exciton binding energy. Transmission electron microscopy results demonstrate that 2D phases are mainly distributed at grain boundaries, reducing defect density and weakening nonradiative recombination. Meanwhile, the p-type doping of perovskite by TCNB optimizes energy level alignment at perovskite/hole transport layer interface. Consequently, PCE of champion device is significantly boosted to 24.01 %. The unencapsulated device retains an initial efficiency close to 94 % after exposure to ambient environment for over 1000 h. This work paves a novel path for designing new mixed-dimensional perovskite solar cells with high PCE and superior stability.     

Long-Term Stability Analysis of 3D and 2D/3D Hybrid Perovskite Solar Cells Using Electrochemical Impedance Spectroscopy

Despite the remarkable progress in perovskite solar cells (PSCs), their instability and rapid degradation over time still restrict their commercialization. A 2D capping layer has been proved to overcome the stability issues; however, an in-depth understanding of the complex degradation processes over a prolonged time at PSC interfaces is crucial for improving their stability. In the current work, we investigated the stability of a triple cation 3D ([(FA_0.83MA_0.17)Cs_0.05]Pb(I_0.83Br_0.17)₃) and 2D/3D PSC fabricated by a layer-by-layer deposition technique (PEAI-based 2D layer over triple cation 3D perovskite) using a state-of-art characterization technique: electrochemical impedance spectroscopy (EIS). A long-term stability test over 24 months was performed on the 3D and 2D/3D PSCs with an initial PCE of 18.87% and 20.21%, respectively, to suggest a more practical scenario. The current-voltage (J-V) and EIS results showed degradation in both the solar cell types; however, a slower degradation rate was observed in 2D/3D PSCs. Finally, the quantitative analysis of the key EIS parameters affected by the degradation in 3D and 2D/3D PSCs were discussed.     

A universal tactic of using Lewis-base polymer-CNTs composites as additives for high performance cm~2-sized and flexible perovskite solar cells

Lewis-base polymers have been widely utilized as additives to act as a template for the perovskite nucleation/crystal growth and passivate the under-coordinated Pb2+ sites.However,it is uncovered in this work that the polymer on the perovskite grain boundaries would significantly hinder the charge transport due to its low conductivity,which brings about free carrier recombination and photocurrent losses.To circumvent this issue while fully exploiting the benefits of polymers in passivating the trap states in perovskite,we incorporate highly conductive multiwall carbon nanotubes(CNTs) with Lewis-base polymers as coadditives in the perovskite film.Functionalizing the CNTs with-COOH group enables a selective hole-extraction and charge transport from perovskite to the hole transporting materials(HTM).By studying the charge transporting and recombination dynamics,we revealed the individual role of the polymer and CNTs in passivating the trap states and facilitating the charge transport,respectively.As a result,the perovskite solar cells(PSCs) with polymer-CNTs composites exhibit an impressive PCE of 21.7% for a small-area device(0.16 cm2) and 20.7% for a large-area device(1.0 cm2).Moreover,due to the superior mechanical flexibility of both polymer and CNTs,the polymer-CNTs composites incorporation in the perovskite film encourages the fabrication of flexible PSCs(f-PSCs) with an impressive PCE of 18.3%,and a strong mechanical durability by retaining 80%of the initial PCE after 1,000 times bending.In addition,we proved that the selection criteria of the polymers can be extended to other long-chain Lewis-base polymers,which opens new possibilities in design and synthesis of inexpensive material for this tactic towards the fabrication of high performance large-area PSCs and f-PSCs.     

Fully Aromatic Self-Assembled Hole-Selective Layer toward Efficient Inverted Wide-Bandgap Perovskite Solar Cells with Ultraviolet Resistance

Ultraviolet-induced degradation has emerged as a critical stability concern impeding the widespread adoption of perovskite solar cells (PSCs), particularly in the context of phase-unstable wide-band gap perovskite films. This study introduces a novel approach by employing a fully aromatic carbazole-based self-assembled monolayer, denoted as (4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)phosphonic acid (MeO-PhPACz), as a hole-selective layer (HSL) in inverted wide-band gap PSCs. Incorporating a conjugated linker plays a pivotal role in promoting the formation of a dense and highly ordered HSL on substrates, facilitating subsequent perovskite interfacial interactions, and fostering the growth of uniform perovskite films. The high-quality film could effectively suppress interfacial non-radiative recombination, improving hole extraction/transport efficiency. Through these advancements, the optimized wide-band gap PSCs, featuring a band gap of 1.68 eV, attain an impressive power conversion efficiency (PCE) of 21.10 %. Remarkably, MeO-PhPACz demonstrates inherent UV resistance and heightened UV absorption capabilities, substantially improving UV resistance for the targeted PSCs. This characteristic holds significance for the feasibility of large-scale outdoor applications.     

Graded interface engineering of 3D/2D halide perovskite solar cells through ultrathin(PEA)_2PbI_4 nanosheets

2D halide perovskites have emerged as promising materials because of their stability and passivation effect in perovskite solar cells(PSCs).However,the introduction of bulky organic ammonium cations from 2D halide perovskites would decrease the device performance generally compared to the traditional 3D MAPbI_3.Incorporation of ultrathin 2D halide perovskite nanosheets(NSs) with 3D MAPbI_3 could address this issue.Herein,we re port a rationally designed PSCs with dimensional graded 3D/2D MAPbI_3/(PEA)2 PbI_4 heterojunction,in which 2D(PEA)2 PbI_4 NSs were synthesized and incorporated between 3D MAPbI_3 and hole-transporting layer.Besides the significantly improved stability,a notable increasement in power conversion efficiency(PCE) of 20% was obtained for the 3D/2D perovskite solar cells due to the favourable band alignment among(PEA)_2 PbI_4 NSs and the other components.The graded structure of MAPbI_3/(PEA)2 PbI_4 would upshift the energy level continuously,which enhances the hole extraction efficiency thus reduces the interface charge recombination,leading to the increasements of VOC from1.04 V to 1.07 V,Jsc from 21.81 mA/cm~2 to 23.15 mA/cm~2 and the fill factor from 67.89% to 74.78%,and therefore an overall PCE of 18.53%.     

Crystallization Regulation by Self-Assembling Liquid Crystal Template Enables Efficient and Stable Perovskite Solar Cells

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC-modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.     

Nucleation and Crystallization in 2D Ruddlesden-Popper Perovskites using Formamidinium-based Organic Semiconductor Spacers for Efficient Solar Cells

The conjugated organic semiconductor spacers have drawn wide attention in two-dimensional (2D) perovskites and formamidinium (FA) has been widely used as A-site cation in high-performance 3D perovskite solar cells (PSCs). However, the FA-based semiconductor spacers have rarely been investigated in 2D Ruddlesden-Popper (RP) perovskites. Here, we developed two FA-based spacers containing thieno[3,2-b]thiophene (TT) and 2,2′-bithiophene (BT) units, namely TTFA and BTFA, respectively, for 2D RP PSCs. The nucleation and crystallization kinetics of TTFA-Pb and BTFA-Pb from sol-gel to film were investigated using in situ optical microscopy and in situ grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. It is found that the TTFA spacer could reduce the energy barrier of nucleation and induces crystal vertical orientation of 2D perovskite by forming larger clusters in precursor solution, resulting in much improved film quality. Benefiting from the enlarged crystal grains, reduced exciton binding energy, and decreased electron-phonon coupling coefficient, the photovoltaic device based on (TTFA)₂MA_n−1Pb_nI_3n+1 (n=5) achieved a champion efficiency of 19.41 %, which is a record for 2D RP PSCs with FA-based spacers. Our work provides deep understanding of the nucleation and crystallization process of 2D RP perovskite films and highlights the great potential of FA-based semiconductor spacers in highly efficient 2D PSCs.     

Antioxidant induced bulk passivation for efficient and stable hole transport layer-free carbon electrode perovskite solar cells

Defect passivation is one of the important strategies to improve the efficiency and stability of perovskite solar cells. In this work, 2,6-di‑tert‑butyl‑4-methylphenol (BHT) as antioxidant was introduced into the perovskite precursor solution to improve the quality of the prepared perovskite films, so that these films performed a larger and uniform grain size. Moreover, the −OH functional group in BHT interacts with I⁻, thus reducing the density of defect states and inhibiting the non-radiative recombination. The presence of hydrophobic groups in BHT protects the film from moisture erosion and improves the long-term stability of PSCs devices. The maximum photoelectric conversion efficiency of the constructed ITO/SnO₂/BHT-MAPbI₃/Carbon device is 16.88%, and the unpackaged cell maintains the initial efficiency of 99.3% after 698 h of storage under the environmental condition of 30% humidity. This work provides an efficient approach to improve the performance of printable hole transport layer-free carbon electrode perovskite solar cells.