Suppressing Thermally Induced Fullerene Aggregation in Organic Solar Cells by Employing Plastic Network

Thermally induced fullerene aggregation restricts the long-term stability in organic solar cells. Herein, we demonstrate an effective method of incorporating cross-linkable small-molecule ethoxylated (2) bisphenol-A dimethacrylate (BPA2EODMA) into poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C 61 butyric acid methyl ester (P3HT:PCBM) blends to form an insoluble framework and inhibit fullerene aggregation. The BPA2EODMA exhibits excellent heat and flexural endurance characteristics, which enhance the thermal and morphological stabilities of the active layer. By systematic research with time-resolved optical spectroscopy and microscopy, the morphological changes and charge-transfer dynamics in P3HT:PCBM blends are explored to unravel the underlying mechanisms for improved photovoltaic efficiency by incorporating the cross-linker. The power conversion efficiency (PCE) increased from 3.6 to 4.2% due to the BPA2EODMA incorporation into the active layer, which is ascribed to the enhancement of exciton dissociation and carrier transportation. After heating at 150 °C for 5 h, the cross-linker-modified devices retained 50% of the initial PCE, whereas the devices without any cross-linker showed 15% PCE retention.