In the last decade, perovskite solar cells (PSCs) have undergone unprecedented rapid development and become a promising candidate for a new-generation solar cell. Among various PSCs, typical 3D halide perovskite-based PSCs deliver the highest efficiency but they suffer from severe instability, which restricts their practical applications. By contrast, the low-dimensional Ruddlesden-Popper (RP) perovskite-based PSCs have recently raised increasing attention due to their superior stability. Yet, the efficiency of RP perovskite-based PSCs is still far from that of the 3D counterparts owing to the difficulty in fabricating high-quality RP perovskite films. In pursuit of high-efficiency RP perovskite-based PSCs, it is critical to manipulate the film formation process to prepare high-quality RP perovskite films. This review aims to provide comprehensive understanding of the high-quality RP-type perovskite film formation by investigating the influential factors. On this basis, several strategies to improve the RP perovskite film quality are proposed via summarizing the recent progress and efforts on the preparation of high-quality RP perovskite film. This review will provide useful guidelines for a better understanding of the crystallization and phase kinetics during RP perovskite film formation process and the design and development of high-performance RP perovskite-based PSCs, promoting the commercialization of PSC technology.

High‐Quality Ruddlesden–Popper Perovskite Film Formation for High‐Performance Perovskite Solar Cells

This work provides an efficient way to facilitate both electron and hole extraction in the designated interfaces of perovskite solar cells. A record power conversion efficiency of 23.6% for mixed Sn–Pb perovskite solar cell devices is realized. 

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Optimized carrier extraction at interfaces for 23.6% efficient tin–lead perovskite solar cells

Fluoroaromatic Cation-Assisted Planar Junction Perovskite Solar Cells with Improved VOC and Stability: The Role of Fluorination Position

Layered hybrid perovskites have emerged as a promising alternative to stabilizing hybrid organic–inorganic perovskite materials, which are predominantly based on Ruddlesden-Popper structures. Formamidinium (FA)-based Dion-Jacobson perovskite analogs are developed that feature bifunctional organic spacers separating the hybrid perovskite slabs by introducing 1,4-phenylenedimethanammonium (PDMA) organic moieties. While these materials demonstrate competitive performances as compared to other FA-based low-dimensional perovskite solar cells, the underlying mechanisms for this behavior remain elusive. Here, the structural complexity and optoelectronic properties of materials featuring (PDMA)FAn–1PbnI3n+1 (n = 1–3) formulations are unraveled using a combination of techniques, including X-ray scattering measurements in conjunction with molecular dynamics simulations and density functional theory calculations. While theoretical calculations suggest that layered Dion-Jacobson perovskite structures are more prominent with the increasing number of inorganic layers (n), this is accompanied with an increase in formation energies that render n > 2 compositions difficult to obtain, in accordance with the experimental evidence. Moreover, the underlying intermolecular interactions and their templating effects on the Dion-Jacobson structure are elucidated, defining the optoelectronic properties. Consequently, despite the challenge to obtain phase-pure n > 1 compositions, time-resolved microwave conductivity measurements reveal high photoconductivities and long charge carrier lifetimes. This comprehensive analysis thereby reveals critical features for advancing layered hybrid perovskite optoelectronics.

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Formamidinium-Based Dion-Jacobson Layered Hybrid Perovskites: Structural Complexity and Optoelectronic Properties

In recent years, 2D Ruddlesden-Popper (2DRP) perovskite materials have been explored as emerging semiconductor materials in solar cells owing to their excellent stability and structural diversity. Although 2DRP perovskites have achieved photovoltaic efficiencies exceeding 19%, their widespread use is hindered by their inferior charge-carrier transport properties in the presence of diverse organic spacer cations, compared to that of traditional 3D perovskites. Hence, a systematic understanding of the carrier transport mechanism in 2D perovskites is critical for the development of high-performance 2D perovskite solar cells (PSCs). Here, the recent advances in the carrier behavior of 2DRP PSCs are summarized, and guidelines for successfully enhancing carrier transport are provided. First, the composition and crystal structure of 2DRP perovskite materials that affect carrier transport are discussed. Then, the features of 2DRP perovskite films (phase separation, grain orientation, crystallinity kinetics, etc.), which are closely related to carrier transport, are evaluated. Next, the principal direction of carrier transport guiding the selection of the transport layer is revealed. Finally, an outlook is proposed and strategies for enhancing carrier transport in high-performance PSCs are rationalized. 

Charge‐Carrier Transport in Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells

Self‐Additive Low‐Dimensional Ruddlesden–Popper Perovskite by the Incorporation of Glycine Hydrochloride for High‐Performance and Stable Solar Cells

Highly efficient and stable perovskite solar cells with strong hydrophobic barrier via introducing poly(vinylidene fluoride) additive

Although the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have made great progress, the surface and interface defects still affect their PCE and stability and hinder the commercialization. To overcome this problem, 1-methylimidazole (1-MIm) and 1-methylbenzimidazole (1-MBIm) are used as the interfacial passivation agents to passivate the defects at surface and interface. The results indicate that, in contrast with 1-MIm, 1-MBIm displays a stronger Lewis coordination interaction with the uncoordinated Pb2+ to reduce the non-radiative recombination and also effectively improves the charge transfer capacity of perovskite films due to its strong π-π conjugate interaction, resulting in the more excellent photovoltaic performance. As a result, the PCE of the champion 1-MBIm PSC has been improved from 19.48% (pristine) to 21.22% with a dramatically enhanced open-circuit voltage (Voc=1.15 V). More importantly, a significantly improvement in long-term stability was achieved for 1-MBIm perovskite devices, which was attributed to the high-quality perovskite film caused by the strong passivation effect of 1-MBIm and the hydrogen bond with water molecules. The results offers an efficient and facile strategy by interface engineering to fabricate high-performance and stable PSCs for commercial application.

Effective Interface Defect Passivation via Employing 1-Methylbenzimidazole for Highly Efficient and Stable Perovskite Solar Cells.

Introduction of 4-hydroxybenzaldehyde as interface modifier with multidimensional defects passivation effect for high-performance perovskite solar cells

Weiwei Wu

Papers

Self‐Additive Low‐Dimensional Ruddlesden–Popper Perovskite by the Incorporation of Glycine Hydrochloride for High‐Performance and Stable Solar Cells

Highly efficient and stable perovskite solar cells with strong hydrophobic barrier via introducing poly(vinylidene fluoride) additive

Effective Interface Defect Passivation via Employing 1-Methylbenzimidazole for Highly Efficient and Stable Perovskite Solar Cells.

Introduction of 4-hydroxybenzaldehyde as interface modifier with multidimensional defects passivation effect for high-performance perovskite solar cells