Bulk Passivation of Molybdenum Trioxide Enables Inverted Organic Photovoltaics with Significantly Enhanced Stability under Extreme Conditions

ABSTRACT While organic photovoltaics (OPVs) have achieved remarkable efficiencies, their practical deployment remains hindered by insufficient stability. Herein, we find that degradation is strongly associated with diffusion‐driven intermixing and redox chemistry at the buried molybdenum trioxide (MoO 3 )/photoactive materials contact region. To address this issue, we incorporate 1H‐isoindole‐1,3(2H)‐dione, 2,2’‐(oxydi‐4,1‐phenylene) bis[3a,4,7,7a‐tetrahydro‐(9CI)] (IPE) into the bulk heterojunction as a bulk passivator that interacts with diffusing MoO 3 species by passivating oxygen vacancies in MoO 3 , thereby suppressing redox reactions between MoO 3 and photoactive materials. The IPE‐containing devices achieve a champion efficiency of 19.06% alongside exceptional thermal robustness, retaining 87.5% of their initial efficiency after thermal aging at 170°C for 5 h (vs. 48.8% for control devices). Critically, under harsh environmental stressors, these devices maintain >80% of their initial efficiency after 500 thermal cycles (−40°C to 85°C, ∼60% relative humidity, ISOS‐T‐3) and over 1150‐h continuous maximum power point tracking under 1 Sun illumination (65°C, ∼50% relative humidity, ISOS‐L‐3). This represents one of the highest stability levels reported for OPVs under the stringent ISOS‐T‐3 and ISOS‐L‐3 protocols. This work provides a generalizable bulk modification strategy to mitigate diffusion‐ and redox‐driven degradation at buried contacts, paving the way for the practical deployment of stable, high‐efficiency OPVs.