Degradation of Poly(3-hexylthiophene):Methano-Fullerene [6,6]-Phenyl-C71 Butyric Acid Methyl Ester Bulk Heterojunction Solar Cells and Annealing Effect on the Degraded Devices

Abstract

We have studied the degradation of poly(3-hexylthiophene):methano-fullerene [6,6]-phenyl-C71 butyric acid methyl ester (P3HT:PC71BM) bulk heterojunction BHJ solar cells and the annealing effect on the degraded devices. Firstly, the modification of electrical properties of the BHJ solar cells was monitored as a function of illumination time. The degradation of BHJ solar cell is dominated by the filling factor reduction and an irradiation to the solar cell accelerates the gradual degradation. Secondly, we found that inserting LiF between Al cathode and active layer, alleviating degradation, improves the device properties of the solar cell as well as its stability. Moreover, annealing on the degraded device helps partially recover the properties of the solar cell and the diode function. We speculated that this partial recovery caused by annealing is attributed to the rearrangement of P3HT as well as the aggregation of PC71BM.