The roles of acceptors in the thermal-degradation of P3HT based organic solar cells

The effects of acceptors on thermal degradation of thin film organic solar cells (OSCs) were investigated under the controlled environment. The popular donor polymer molecule, poly(3-hexylthiophene) (P3HT) is used in the preparation of bulk-heterojunction (BHJ) organic solar absorber medium. The evidences of degradation were observed from the changes of the optical and morphological properties of the polymer film. The parameters gathered from various characterization methods suggest that film degradation is indeed dependent on the nature of acceptor molecules used in the polymer matrix. Interestingly, the PC60BM acceptor blend solar absorber films are found to be more stable than ITIC based polymer blend. These are evident on the measured device parameters such as J(sc) and V-oc values that contribute to poor performance in P3HT:ITIC-based devices. It has been noted that a 50% drop in open-circuit voltage was recorded in ITIC based solar cell within an hour of thermal degradation. The FTIR result revealed that the production of-OH groups as a result of oxidation leads to the creation of trap states that hinder conductivity by decreasing short-circuit current.