Metal halide perovskite solar cells (PSCs) are anticipated to play a pivotal role in the next generation of photovoltaic technologies, but their unsatisfactory stability hinders further commercial applications. Particularly, numerous interfacial defects and poor mechanical adhesion at the perovskite buried interface present a critical obstacle hindering power conversion efficiency (PCE) and long-term stability of PSCs. Here, different from conventional small-molecule or linear polymer interface modifiers, we introduce a star-shaped PMMA-b-PDMAEMA (S-MD, where PMMA = poly(methyl methacrylate) and PDMAEMA = poly(dimethylaminoethyl methacrylate)) polymer as a multifunctional bridge-linking polymer for simultaneous defect passivation and mechanical reinforcement at the buried interface of inverted (p–i–n) PSCs. S-MD features a three-dimensional architecture with multiple extended conjugated arms, offering multiple Lewis base functional groups (e.g., C=O and R–N(CH₃)₂) with a high density of multidentate coordination sites. These groups can effectively coordinate with electron-deficient defects at the perovskite buried interface, enabling improved crystallization, reduced defect density, and enhanced interfacial adhesion. As a result, the interfacial fracture strength increases from 0.13 to 1.66 MPa. The resultant device achieves a PCE of 26.35% (certified steady-state PCE of 25.96%). The flexible device retains over 90% of its initial efficiency after 3000 flexing cycles at a curvature radius of 6 mm (R = 6 mm). This work highlights a multidentate coordinating, star-shaped polymer interface strategy that offers a promising pathway toward highly efficient and stable inverted PSCs.

An inverted planar heterojunction perovskite solar cell (PSC) is one of the most competitive photovoltaic devices exhibiting a high power conversion efficiency (PCE) and nearly free hysteresis in the voltage–current output. However, the band alignment between the transport materials and the perovskite absorber has not been optimized, resulting in a lower open-circuit voltage (V_oc) than that of regular PSCs. To address this issue, we tune the band alignment in perovskite photovoltaic architecture by introducing bilayer structured transport materials, e.g., the hole transport material poly(ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT: PSS)/V₂O₅. In this study, solution processed inorganic V₂O_x interlayer is incorporated into PEDOT: PSS for achieving improved film surface properties as well as optical and electrical properties. For example, the work function (WF) was changed from 5.1 to 5.4 eV. A remarkably high PCE of 17.5% with nearly free hysteresis and a stabilized efficiency of 17.1% have been achieved. Electronic impedance spectra (EIS) demonstrate a significant increase in the recombination resistance after introducing the interlayer, associated with the high V_oc output value of 1.05 V. Transient photocurrent and photovoltage measurements indicate that a comparable charge transport process and an inhibited recombination process occur in the PSC with the introduction of the V₂O_x interlayer.