Temperature-dependent morphology evolution of P3HT:PCBM blend solar cells during annealing processes

In this paper, the morphology evolution of [6,6]-phenyl-C-61(or 71)-butyric acid methyl ester (PC61BM or PC71BM) in poly(3-hexylthiophene) (P3HT) annealed at different temperatures was investigated. One result which was observed is that PCBM clusters aggregate more readily at higher annealing temperatures. The aggregation of PCBM could be avoided after coating the Al layer on the active layer, which is due to the hindering effect of the Al layer for the formation of PCBM clusters. SEM images show that the active layer with Al coating is smoother than that without Al layer. The performance of so-fabricated devices was analyzed with different annealing temperatures. Open-circuit voltage, fill factor and power conversion efficiency (PCE) of the devices were improved subsequently with increased annealing temperatures, while the absorption intensity of the devices was also improved. The P3HT:PC61BM and P3HT:PC71BM blend devices had highest PCEs of 4.55% and 4.84%, respectively. Crystallinity of the active layer is raised with higher annealing temperatures, which may result in the increased performance of devices.

► PCBM clusters aggregate more readily at higher annealing temperatures.
► The aggregation of PCBM could be avoided after coating the Al layer on the active layer.
► PCE of the devices were improved subsequently with increased annealing temperatures.
► The P3HT:PC61BM and P3HT:PC71BM blend devices had obtained the PCE of 4.55% and 4.84%, respectively.