Suppressing Thermal Aggregation of Fullerene Enables ISOS‐L‐3 Stable Inverted Perovskite Solar Cells

ABSTRACT Inverted perovskite solar cells (PSCs), as the promising candidates for practical photovoltaics, always undergo severe degradation under standard commercial testing conditions (ISOS‐L‐3, 1 sun + RH≥50% + 85°C), posing a major obstacle to their commercialization. One of the inherent bottlenecks lies on that the fullerenes would spontaneously aggregate into crystalline clusters at high temperature, causing the irreversible interface destruction. Herein, drawing inspiration from the bionic spider web, “fullerene‐fixed web” is constructed to firmly immobilize [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) molecules via in situ polymerized 3‐aminopropyltrimethoxysilane (APTMS)‐derived siloxane network. The hydrolyzed and polymerized APTMS forms a robust 3D framework that confines PCBM through strong hydrogen‐bonding interactions, thereby suppressing its thermal aggregation. Simultaneously, the exposed amino groups of the network passivate the perovskite surface defects and strengthen the perovskite/ETL interfacial coupling. As a result, the target inverted PSCs achieve a champion efficiency of 26.39% (certified 26.27%) and retain over 90% of initial performance after 800 h age under ISOS‐L‐3 condition—significantly outperforming the control (24.98%, T 90 < 250 h). This work provides a feasible and effective pathway toward achieving highly efficient and photothermally durable perovskite photovoltaics.