Isomerized Conjugated Molecules as Hole‐Selective Contacts for Inverted Perovskite Solar Cells

Hole‐selective contacts, as a crucial component in perovskite solar cells (PSCs), have attracted significant research interest owing to their solution‐processability, high device performance, and long‐term stability. Despite their effectiveness in interfacial modification and hole extraction, their defect passivation capability is limited by the absence of exocyclic functional atom coordinating with lead iodide. Here, two isomeric derivatives, (2‐(benzo[b]benzo[4,5]thieno[2,3‐d]thiophen‐2‐yl)ethyl)phosphonic acid (BTBT‐L) and (2‐(benzo[b]benzo[4,5]thieno[2,3‐d]thiophen‐4‐yl)ethyl)phosphonic acid (BTBT‐Z) are reported. BTBT‐L exhibits a linear structure, while BTBT‐Z adopts a zig–zag configuration with one sulfur atom positioned opposite to the anchoring group. Compared with BTBT‐L, BTBT‐Z exhibits a higher electron density on the thiophene sulfur atom and a larger molecular dipole moment, inducing enhanced hole extraction and transport capability. Furthermore, BTBT‐Z demonstrates improved defect passivation capability at the buried interface of the perovskite layer, promoting enhanced crystallization and thin‐film quality, thereby leading to higher power conversion efficiency (PCE) and better operational stability. With the rationally designed BTBT‐Z to modify the indium tin oxide substrate, the inverted PSC achieves a champion efficiency of 25.1% with improved device stability, retaining over 90% of the initial PCE after continuous maximum power point tracking under 1‐sun irradiation for 1000 h.