Conformal Imidazolium 1D Perovskite Capping Layer Stabilized 3D Perovskite Films for Efficient Solar Modules

Self-Induced A-B-A Structure Enables Efficient Wide-Bandgap Perovskite Solar Cells and Tandems

Wide-bandgap (WBG) perovskite solar cells (PSCs), due to their tunable bandgap, can be integrated into tandem cell configurations with narrow-bandgap solar cells to overcome the shockley-queisser (SQ) limitation. However, the main obstacles limiting their performance are poor crystallinity and light-induced halide segregation. To achieve high performance in WBG PSCs, this study reports a dual-molecule cooperative strategy involving the introduction of 1-benzyl-3-methylimidazolium bromide (BzMIM Br) as an additive and the introduction of 6-fluoropyrimidine-2,4- diamine (DMFP) as a passivation layer. DMFP self-induced penetration to the bottom of the perovskite, forming an A-B-A structure with BzMIM Br, through utilizing multisite integration with uncoordinated Pb2+, constructing internal molecular bridges. Research findings indicate that the A-B-A structure with uniform potential distribution can interact with the perovskite in a step-like manner, suppressing halide segregation, and replenishing the vacancy defects. Results demonstrate power conversion efficiencies (PCEs) of 22.77% and 18.54% for inverted PSCs with effective areas of 0.043 and 1.0 cm2, respectively. Unencapsulated devices retain 95% of initial efficiency after 1500 h of continuous illumination under one-sun equivalent conditions in a nitrogen atmosphere. Additionally, the PCE of the prepared semi-transparent WBG devices reached 19.60%, while the PCE of the 4-terminal all-perovskite tandem device reached 26.18%.

Formation Dynamics of Thermally Stable 1D/3D Perovskite Interfaces for High-Performance Photovoltaics

Direct understanding of the formation and crystallization of low-dimensional (LD) perovskites with varying dimensionalities employing the same bulky cations can offer insights into LD perovskites and their heterostructures with 3D perovskites. In this study, the secondary amine cation of N-methyl-1-(naphthalen-1-yl)methylammonium (M-NMA+) and the formation dynamics of its corresponding LD perovskite are investigated. The intermolecular π-π stacking of M-NMA+ and their connection with inorganic PbI6 octahedrons within the product structures control the formation of LD perovskite. In an N,N-dimethylformamide (DMF) precursor solution, both 1D and 2D products can be obtained. Interestingly, due to the strong interaction between M-NMA+ and the DMF solvent, compared to the 1D phase, the formation of 2D perovskites is uniquely dependent on heterogeneous nucleation. Nevertheless, post-treatment of 3D perovskite films with an isopropanol solution of M-NMAI leads to the exclusive formation of thermally stable 1D phases on the surface. The resulting 1D/3D heterostructure facilitates perovskite solar cells (PSCs) to not only achieve a record efficiency of 25.51% through 1D perovskite passivation but also significantly enhance the thermal stability of unencapsulated devices at 85 °C. This study deepens the understanding of the formation dynamics of LD perovskites and offers an efficient strategy for fabricating stable and high-performance PSCs.

Dimensional engineering of interlayer for efficient large-area perovskite solar cells with high stability under ISOS-L-3 aging test

The utilization of low-dimensional perovskites (LDPs) as interlayers on three-dimensional (3D) perovskites has been regarded as an efficient strategy to enhance the performance of perovskite solar cells. Yet, the formation mechanism of LDPs and their impacts on the device performance remain elusive. Herein, we use dimensional engineering to facilitate the controllable growth of 1D and 2D structures on 3D perovskites. The differences of isomeric ligands in electrostatic potential distribution and steric effects for intermolecular forces contribute to different LDPs. The 1D structure facilitates charge transfer with favored channel orientation and energy level alignment. This approach enables perovskite solar modules (PSMs) using 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene to achieve an efficiency of 20.20% over 10 by 10 square centimeters (cm2) and 22.05% over 6 by 6 cm2. In particular, a PSM (6 by 6 cm2) using poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] maintains an initial efficiency of ~95% after 1000 hours under the rigorous ISOS-L-3 accelerated aging tests, marking a record for the highest stability of n-i-p structure modules.

Highly Efficient and Stable Perovskite Solar Modules Based on FcPF6 Engineered Spiro-OMeTAD Hole Transporting Layer

Li-TFSI doped spiro-OMeTAD is widely recognized as a beneficial hole transport layer (HTL) in perovskite solar cells (PSCs), contributing to high device efficiencies. However, the uncontrolled migration of lithium ions (Li+) during device operation has impeded its broad adoption in scalable and stable photovoltaic modules. Herein, an additive strategy is proposed by employing ferrocenium hexafluorophosphate (FcPF6) as a relay medium to enhance the hole extraction capability of the spiro-OMeTAD via the instant oxidation function. Besides, the novel Fc-Li interaction effectively restricts the movement of Li+. Simultaneously, the dissociative hexafluorophosphate group is cleverly exploited to regulate the unstable iodide species on the perovskite surface, further inhibiting the formation of migration channels and stabilizing the interfaces. This modification leads to power conversion efficiencies (PCEs) reaching 22.13% and 20.27% in 36 cm2 (active area of 18 cm2) and 100 cm2 (active area of 56 cm2) perovskite solar modules (PSMs), respectively, with exceptional operational stability obtained for over 1000 h under the ISOS-L-1 procedure. The novel FcPF6-based engineering approach is pivotal for advancing the industrialization of PSCs, particularly those relying on high-performance spiro-OMeTAD- based HTLs.

Anions Regulation of 1D Perovskite Intrusion-Behavior for Efficient and Stable Perovskite Solar Cells

Constructing a 1D/3D perovskite heterojunction has recently emerged as a prevalent approach for elevating the efficiency and stability of perovskite solar cells (PSCs), due to the excellent defect-passivation capacity and enhanced resistance to water and oxygen of 1D perovskite. However, the 1D perovskite commonly exhibits much poorer charge carrier transport ability when compared with its 3D counterpart. Tailoring the intrusion depth of a 1D perovskite into the 1D/3D heterojunction is thus of key importance for PSCs but remains a great challenge. We introduce herein a novel anion-regulation strategy that can effectively tune the intrusion behavior of 1D perovskite into 3D perovskite to form a 1D/3D heterojunction with gradual structure and gradient energy-level alignment. This gradual 1D/3D-perovskite interface leads to outstanding defect passivation performance, together with a desired balance between charge transport and moisture/oxygen blocking. Consequently, the PSCs with a 1D/3D perovskite heterojunction resulting from tetra-n-butylammonium acetate (TBAAc) treatment yield a remarkable enhancement in power conversion efficiency (PCE) from 18.4 to 20.1%. The unencapsulated device also demonstrates excellent stability and retains 90% of its initial PCE after 2400 h of storage in the air atmosphere with 30 ± 5% humidity at 25 ± 5 °C.

Long-chain organic molecules enable mixed dimensional perovskite photovoltaics: a brief view

The remarkable optoelectronic properties of organometal halide perovskite solar cells have captivated significant attention in the energy sector. Nevertheless, the instability of 3D perovskites, despite their extensive study and attainment of high-power conversion efficiency, remains a substantial obstacle in advancing PSCs for practical applications and eventual commercialization. To tackle this issue, researchers have devised mixed-dimensional perovskite structures combining 1D and 3D components. This innovative approach entails incorporating stable 1D perovskites into 3D perovskite matrices, yielding a significant improvement in long-term stability against various challenges, including moisture, continuous illumination, and thermal stress. Notably, the incorporation of 1D perovskite yields a multitude of advantages. Firstly, it efficiently passivates defects, thereby improving the overall device quality. Secondly, it retards ion migration, a pivotal factor in degradation, thus further bolstering stability. Lastly, the inclusion of 1D perovskite facilitates charge transport, ultimately resulting in an elevated device efficiency. In this succinct review, we thoroughly encapsulate the recent progress in PSCs utilizing 1D/3D mixed-dimensional architectures. These advancements encompass both stacked bilayer configurations of 1D/3D structures and mixed monolayer structures of 1D/3D. Additionally, we tackle critical challenges that must be surmounted and offer insights into the prospects for further advancements in this domain.

Modulation of Buried Interface by 1-(3-aminopropyl)-Imidazole for Efficient Inverted Formamidinium-Cesium Perovskite Solar Cells

Considering the direct influence of substrate surface nature on perovskite (PVK) film growth, buried interfacial engineering is crucial to obtain ideal perovskite solar cells (PSCs). Herein, 1-(3-aminopropyl)-imidazole (API) is introduced at polytriarylamine (PTAA)/PVK interface to modulate the bottom property of PVK. First, the introduction of API improves the growth of PVK grains and reduces the Pb2+ defects and residual PbI2 present at the bottom of the film, contributing to the acquisition of high-quality PVK film. Besides, the presence of API can optimize the energy structure between PVK and PTAA, which facilitates the interfacial charge transfer. Density functional theory (DFT) reveals that the electron donor unit (R-C ═ N) of the API prefers to bind with Pb2+ traps at the PVK interface, while the formation of hydrogen bonds between the R-NH2 of API and I- strengthens the above binding ability. Consequently, the optimum API-treated inverted formamidinium-cesium (FA/Cs) PSCs yields a champion power conversion efficiency (PCE) of 22.02% and exhibited favorable stability.

Post-Treatment-Free Dual-Interface Passivation via Facile 1D/3D Perovskite Heterojunction Construction

For achieving high-efficiency perovskite solar cells, it is almost always necessary to substantially passivate defects and protect the perovskite structure at its interfaces with charge transport layers. Such a modification generally involves the post-treatment of the deposited perovskite film by spin coating, which cannot meet the technical demands of scaling up the production of perovskite photovoltaics. In this work, we demonstrate one-step construction of buried and capped double 1D/3D heterojunctions without the need for any post-treatment, which is achieved through facile tetraethylammonium trifluoroacetate (TEATFA) prefunctionalization on the SnO2 substrate. The functional TEATFA salt is first deposited onto the SnO2 substrate and reacts on this buried interface. Once the FAPbI3 perovskite precursor solution is dripped, a portion of the TEA+ cations spontaneously diffuse to the top surface over film crystallization. The TEATFA-based water-resistant 1D/3D TEAPbI3/FAPbI3 heterojunctions at both the buried and capped interfaces lead to much better photovoltaic performance and higher operational stability. Since this approach saves the need for any postsynthesis passivation, its feasibility for the fabrication of large-area perovskite photovoltaics is also showcased. Compared to ∼15% for a pristine 5 cm × 5 cm FAPbI3 mini-module without postsynthesis passivation, over 20% efficiency is achieved following the proposed route, demonstrating its great potential for larger-scale fabrication with fewer processing steps.

Tailoring passivators for highly efficient and stable perovskite solar cells

There is an ongoing global effort to advance emerging perovskite solar cells (PSCs), and many of these endeavours are focused on developing new compositions, processing methods and passivation strategies. In particular, the use of passivators to reduce the defects in perovskite materials has been demonstrated to be an effective approach for enhancing the photovoltaic performance and long-term stability of PSCs. Organic passivators have received increasing attention since the late 2010s as their structures and properties can readily be modified. First, this Review discusses the main types of defect in perovskite materials and reviews their properties. We examine the deleterious impact of defects on device efficiency and stability and highlight how defects facilitate extrinsic degradation pathways. Second, the proven use of different passivator designs to mitigate these negative effects is discussed, and possible defect passivation mechanisms are presented. Finally, we propose four specific directions for future research, which, in our opinion, will be crucial for unlocking the full potential of PSCs using the concept of defect passivation.