Nano-scale mechanical properties of polymer/fullerene bulk hetero-junction films and their influence on photovoltaic cells

Mechanical properties of poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend films, prepared under different processing conditions, were evaluated by nanoindentation. Photovoltaic devices fabricated using above active layers presented the highest power conversion efficiencies for blend films having lowest Young’s modulus (20.73 GPa) and hardness (649 MPa), as measured by a nanoidentator under optimized conditions of blend proportion (1:1), film drying rate (slow) and annealing temperature and time (110 °C and 10 min). It implies that the degree of nano-scale phase separation for the P3HT:PCBM blend is strongly correlated with the mechanical properties in the nanodimension. The nanoindentation is a method to estimate nano-scale mechanical properties of blend films and the performance of photovoltaic cells.

Graphical Abstract
► Nano-scale mechanical properties of polymer bulk-junction films are studied by nanoindentation.
► The device of the highest power conversion efficiency also has the P3HT:PCBM film of the lowest Young's modulus (E) as well as lowest the hardness (H).
► The most favorable nano-scale phase separation of blend components manifests in the mechanical properties in the nano dimension.Figure optionsDownload as PowerPoint slide