in dramatically improved environmental and structural stability. [2,3] However, the exciton binding energy of layered phases in 2D perovskites could be as high as 300 meV although this value could be reduced with the increased thickness of inorganic layer, resulting in relatively inferior photovoltaic performance compared to 3D perovskite solar cells (PSCs). [13] Thus, it is urgent to develop more efficient organic spacers as well as device engineering to obtain both highly efficient and stable 2D PSCs for future industry application.Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) structures are two main archetypes of layered 2D perovskites to date. [14][15][16][17][18][19] The general formula of a 2D RP and DJ perovskite is (L′) 2 A n−1 M n X 3n+1 and (L″)A n−1 M n X 3n+1 , where L′ and A are monovalent cations, L″ is a divalent organic cation, M is a divalent metal cation, X is a halide ion, and n is the number of corner-sharing [MX 6 ] 4− octahedral slabs. [5] Typically, a van der Waals gap exist in organic spacers between adjacent inorganic [MI 6 ] 4octahedron slabs in 2D RP perovskites. [1] 2D RP perovskites have been shown enhanced stability, while the weak interlayer interactions in 2D RP perovskites with obvious van der Waals gaps cannot sufficiently stabilize their layered structure. In contrast, charge transport and stability could be enhanced in 2D DJ perovskites, where the neighboring inorganic slabs were bridged by diammonium spacers, resulting in shortened interslab distance and eliminated van der Waals gap. [1] So far, the aliphatic diammonium spacers, such as 1,4-butanediamine (BDA) and 1,3-propanediamine (PDA), have been studied in 2D DJ perovskite devices with promising photovoltaic performance. [20][21][22] However, the electrically insulating aliphatic diammonium spacers could block efficient charge transport due to their low dielectric constant. [23] In comparison with the aliphatic spacers, the aromatic spacers typically exhibit a larger dielectric constant and better conductivity due to the delocalized π-electrons along the molecular backbone, which could weaken the dielectric confinement effect by reducing dielectric mismatch between corner-sharing inorganic slabs and adjacent organic spacer layer. [23][24][25] Recently, several aromatic diammonium cations such as pyridinium-based aromatic spacers (3AMP, 4AMP), phenyl-based aromatic spacer (PDMA) and thiophene-based aromatic spacer (ThDMA) have been developed as organic spacers in 2D DJ PSCs to enhance the device performance. [23,[26][27][28][29][30] These single aromatic ringbased bulky spacers used so far still cannot directly contribute 2D Dion-Jacobson (DJ) perovskites have become an emerging photovoltaic material with excellent structure and environmental stability due to their lacking van der Waals gaps relative to 2D Ruddlesden-Popper perovskites. Here, a fused-thiophene-based spacer, namely TTDMAI, is successfully developed for 2D DJ perovskite solar cells. It is found that the DJ perovskite using TTDMA spacer with extended π-conjuga...