Morphology Tuning of ZnO/P3HT/P3HT-b-PEO Hybrid Films Deposited via Spray or Spin Coating.

Hybrid films of zinc oxide (ZnO) and poly(3-hexylthiophen-2,5-diyl) (P3HT) show promising characteristics for application in hybrid bulk heterojunction solar cells (HBSCs). However, the incompatibility of ZnO and P3HT may lead to a reduced interface area, thus reducing the probability of exciton separation and consequently lowering solar cells efficiencies. Here, a diblock copolymer P3HT-b-poly(ethylene oxide) (PEO) is introduced to improve the interface between ZnO and P3HT. ZnO is synthesized via a block copolymer assisted sol-gel approach and the used zinc precursor is directly incorporated into the PEO blocks. Thus, the possibility of aggregation is reduced for both, the inorganic and the organic components and a good intermixing is ascertained. Two deposition methods, namely spray and spin coating are compared with respect to the resulting film structure, which is investigated with scanning electron microscopy (SEM) and time-of-flight grazing-incidence small-angle neutron scattering (TOF-GISANS) measurements. Both, the surface and inner morphologies reveal that the spin coated samples possess smaller and less diverse domain sizes than the sprayed films. Due to the advantage of spray coating in large-scale production, the morphology of the sprayed samples is tailored more meticulous by changing the weight fraction of ZnO in the films. The sprayed hybrid films show smaller domains and less aggregation with decreasing amount of ZnO. This reveals that both, the deposition method and composition of the ZnO/P3HT/P3HT-b-PEO hybrid films play an important role for the film morphology and thus for improving the performance of HBSCs in future application.