2026/06/12 by Tzu‐Yen Huang, Anton P. Le Brun, Benedikt Sochor +3 · 1 voice
Engineering · Materials Science · #Block Copolymer Self-Assembly #Organic Electronics and Photovoltaics #Perovskite Materials and Applications
paper · doi:10.1021/acsaem.6c00922
openalex publication_date 2026/06/12 · openalex created_date 2026/06/13 · openalex updated_date 2026/07/15
The thermal stability of bulk heterojunction (BHJ) active layers critically determines the lifetime of nonfullerene organic solar cells. In this work, we track the thermally driven kinetic evolution of PffBT4T-2OD:ITIC BHJs over a range of annealing temperatures and times. Neat PffBT4T-2OD films remain stable under the investigated conditions, whereas neat ITIC films develop progressively diffuse interfaces and show the onset of structural evolution upon annealing at 120 °C. In pristine PffBT4T-2OD:ITIC BHJs, annealing above 120 °C triggers vertical phase stratification, forming an ITIC-enriched layer near the air interface and a PffBT4T-2OD-rich region adjacent to the substrate. Time-resolved neutron reflectometry provides quantitative kinetic evidence that incorporating a small amount of a solvent additive (1,8-diiodooctane, DIO, 0.25 vol %) delays and mitigates thermally induced vertical redistribution. Specifically, DIO incorporation extends the extrapolated onset time for redistribution by ∼2.3-fold, accompanied by an ∼38% reduction in the redistribution rate. Complementary X-ray scattering further shows that the development of ITIC crystalline ordering is delayed in the presence of DIO. These results demonstrate an additive-assisted kinetic stabilization pathway in nonfullerene BHJs, where improved donor–acceptor intermixing slows early-stage acceptor ordering and mitigates progression toward larger-scale phase separation under thermal stress.