Enhanced Stability and Optimized Morphology Induced by Electric-Field-Assisted Annealing of Bulk Heterojunction Solar Cells

The utility of electric fields during the bulk heterojunction (BHJ) film drying process for tuning the morphology and stability of the device is demonstrated. An external electric-field-assisted annealing (EFTA) treatment is used to engineer the stability of amorphous donor polymer-based BHJs without compromising device performance. Residual additive in the device post fabrication is a major source of degradation. Thermal annealing of an active layer effectively removes residual additive, which in case of amorphous polymer donor-based BHJs, however, leads to unfavorable changes in the morphology. The detrimental effect of thermal annealing in amorphous donor polymer-based solar cells is mitigated by the presence of an electric field during the drying stage. The complete removal of additive is ensured by this treatment procedure and leads to improved packing and a rigid morphology. The structural stability is reflected in the performance parameters monitored over the long term and electrical noise measurements. The magnitude and polarity of the applied electric field are observed to control the vertical distribution of donor and acceptor components.