The surface area and structure of adsorbents are crucially important to its adsorption capacity. Herein, we focused on the correlation between the structures of 2D/3D materials and its adsorption properties by taking three kinds of cobalt−aluminum layered double hydroxide (CoAl-LDH) as adsorbents, including a 3D hierarchical flower-like hollow/solid sphere (FH/FS-CoAl) and 2D plate (P-CoAl). As expected, FH-CoAl showed the highest adsorption capacity (∼2189.23 mg/ g) for methyl orange (MO), benefiting from the highly accessible surface areas and more active sites of unique hollow structural characteristics inherited from the hierarchical flower-like hollow structures. Interestingly, compared with FS/FH-CoAl, P-CoAl exhibited the highest adsorption capacity enhancement times after being normalized with surface area, but displayed an inferior maximum adsorption capacity. The reasons could be mainly ascribed to (1) P-CoAl with 2D plate structures possessed more fully exposed active sites than FH-CoAl and (2) the compact and thick shell structure of the hollow structure made dye difficult to diffuse into the hollow interior. Moreover, the characterization analysis further confirmed that the electrostatic interaction, hydrogen bonding, and ion exchange were the main adsorption mechanisms for FH-CoAl and FS-CoAl, while electrostatic interaction was mainly an adsorption mechanism for P-CoAl. A deep understanding of synergistic modulation of surface area and structure effects of 2D/3D adsorbents will provide the opportunity for further enhancing the adsorption activity and offer a new pathway for design and optimization of advanced adsorbents in the near future.

commercial modules, respectively), excellent stability (>25 years guaranteed lifetime), low cost (<$0.30 per peak watt), and mature production lines. [1] Further improving power conversion efficiency (PCE) is the most effective way to reduce the cost of solar electricity. Nevertheless, the record PCE of single-junction Si solar cells is approaching its theoretical limit of 29.4%. [2] Tandem solar cells are widely regarded as the most promising strategy to break the Shockley-Queisser (S-Q) efficiency limit [3] since they can reduce the thermal relaxation energy loss of highenergy photons. [4] Theoretical calculations show that in double-junction Si-based tandem solar cells, the top cells should have a ≈1.7 eV bandgap (E g ) and tandem solar cells could achieve an efficiency limit of ≈45% [5] (Figure 1a).At present, III-V compounds and halide perovskites with a 1.7 eV bandgap are the most promising top cells for Si-based tandem solar cells (Figure 1a). [1b] Both of their single-junction and Si-based tandem solar cells have achieved >20% and >29% efficiency, respectively. [6] Nevertheless, they both suffer from obvious drawbacks. III-V photovoltaics are stable and highly efficient; however, they require sophisticated fabrication procedures and expensive fabrication equipment, leading to the prohibitive cost (≈$150 per peak watt) [7] and limited deployment. As for halide perovskites, they could be directly processed, either via solution processing or thermal evaporation, onto Si bottom solar cells without sacrificing device performance. Currently, two-terminal perovskite/Si tandem solar cells have achieved a record efficiency of 29.8%, but the long-term stability of perovskite top cells is not fully resolved. [8] Overall, what is the best choice as the top cell for Si-based tandem devices is still an open question in the field. It is thus highly valuable to explore new absorber materials for the top cell.Various semiconductors with ≈1.7 eV bandgap, such as amorphous-Si (a-Si), Zn x Cd 1-x Te, CuGaSe 2, and Sb 2 S 3 , have been considered as the alternative top cells over the past years (Table 1). A-Si sounds promising in terms of the simple chemical element, low fabrication cost, and large absorption coefficient. In 1990, an impressive efficiency of 15.04% has been achieved for two-terminal a-Si/c-Si tandem solar cells, but no progress was made since then due to its complex defects and the band tail state effect. [9] Wide bandgap Zn x Cd 1-x Te and CuGaSe 2 , originating from the commercial CdTe and Cu(In,Ga)Se 2 solar cells, Silicon-based tandem solar cells are regarded as one of the most feasible ways to break the single-junction Shockley-Queisser limit efficiency and further reduce the cost of solar electricity. Recently, wide-bandgap (≈1.7 eV) perovskite solar cells have drawn intense research interest as the top cell for Si-based tandem devices. Despite significant progress in device efficiency, the unsatisfactory stability of perovskites is still a huge concern. Besides halide perovskites, there are many in...