Surface energy (γs) plays a key role in the formation of bulk-heterojunction (BHJ) films in organic solar cells fabricated by solution process. The miscibility of BHJ films can be predicted by the difference of surface energy between donor and acceptor. The vertical distribution and the stacking orientation of BHJ films can be regulated by the surface energy in the bottom interface layer. The surface energy of thin film is usually obtained by measuring contact angle using Owens-Wendt model.
source https://phys.org/news/2021-10-strategy-interfacial-modification-solar-cells.html