Engineering strategies for two-dimensional perovskite solar cells

Two-dimensional perovskites can be used to improve the robustness of an absorber or provide protection for vulnerable 3D counterparts due to their multiple-quantum-well structure, high hydrophobicity, and superior thermal and light stability, thereby providing an effective pathway to the enhancement of device stability. Tuning the composition of 2D perovskites induces change of the lattice structure and optoelectronic properties, substantially affecting the device stability and allowing the development of lead-free perovskite solar cells (PSCs). Achieving simultaneously high efficiency and high stability of PSCs with 2D perovskites requires the application of appropriate engineering strategies, such as dimensional, interfacial, and tandem cell engineering, profiting from the strengths of both 2D and 3D materials. Perovskite solar cells (PSCs) face the challenge of degradation due to the vulnerability of perovskites to environmental factors. Two-dimensional (2D) perovskite materials allow the enhancement of absorber robustness or provide protection for vulnerable 3D counterparts, leading to improved stability of PSCs. However, the improved stability comes at the expense of efficiency; additional engineering strategies are needed to achieve simultaneously high efficiency and stability. Herein, we summarize the crystal structure and characteristics of different 2D perovskite materials and the performance of the PSCs with each type. In addition, the contributions of 2D perovskites to the improvement of device stability and efficiency are systematically analyzed from the point of view of compositional, dimensional, interfacial, and tandem cell engineering. Perovskite solar cells (PSCs) face the challenge of degradation due to the vulnerability of perovskites to environmental factors. Two-dimensional (2D) perovskite materials allow the enhancement of absorber robustness or provide protection for vulnerable 3D counterparts, leading to improved stability of PSCs. However, the improved stability comes at the expense of efficiency; additional engineering strategies are needed to achieve simultaneously high efficiency and stability. Herein, we summarize the crystal structure and characteristics of different 2D perovskite materials and the performance of the PSCs with each type. In addition, the contributions of 2D perovskites to the improvement of device stability and efficiency are systematically analyzed from the point of view of compositional, dimensional, interfacial, and tandem cell engineering. the formula of a 2D ACI perovskite is BAnMnX3n+1 (B, divalent organic cation; A, univalent organic cation; M, metal; X, halide; n = 1, 2, …, ∞) and an alternating cation arrangement is constructed by the larger B and smaller A cations in the interlayer space. the change of dielectric properties of a whole system due to the incorporation of nanoparticles and/or 2D materials and the resulting modification of interface and inner magnetic field. a perovskite with formula BAn−1MnX3n+1 (n = 1, 2, …, ∞). a bound electron–hole pair in a semiconducting or insulating material. the perovskite conductor layers with high conductivity function as the potential ‘well’ (the preferred location for charge transport) and the insulating spacer cations foster the formation of the potential ‘wall’. the number of inorganic layers that can be tuned by the stoichiometry of precursor. the degeneracy of the carrier spin states within the conduction and/or valence bands as a consequence of spin–orbit interaction between the spin and the momentum of electrons under broken inversion symmetry. combination of an excited electron and hole after charge separation. represented by a formula of A′2An-1MnX3n+1 (A and A′, univalent organic cations; n = 1, 2, …, ∞), consisting of conductor layer, (An-1MnX3n+1) and isolation layer (A′, e.g., organic aliphatic or aromatic alkylammonium cation). the splitting of orbital energy level caused by the interaction between particle spin and orbital momentum.