Nanostructured morphology of P3HT:PCBM bulk heterojunction solar cells

Organic bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) and the fullerene derivative (PCBM) were fabricated and nanostructured morphology were investigated. Bulk heterojunction solar cells were fabricated with concentration ratio 1:0.5, 1:1 and 1:2 of P3HT and PCBM. Nanostructured morphology of P3HT:PCBM composite films were investigated with annealing temperature and variation of composition ratio, which were correlated with device performance. Fabricated solar cells annealed at 150 °C show much better device performance than that of the cells without annealing. Transmission electron microscopy (TEM) study shows formation of PCBM nanocrystals in the P3HT composite film with annealing. The formations of elongated PCBM nanocrystals provide an efficient percolation path for the electron, thereby improving device performance. Better device performance was observed with 1:1 as compared to 1:0.5 and 1:2 concentration ratios of P3HT and PCBM. With decrease in PCBM content, there were no efficient percolation paths for electron; on the other hand there were poorer intermolecular packing with increased PCBM content leading to lower device performance.