Manipulation and Direct Characterization of Polymer/Small-Molecule Interface Morphology in Bulk-Heterojunction Solar Cell

Abstract

To investigate the effect of miscibility between conjugatedpolymers(CPs) and Y6 on bulk-heterojunction (BHJ) type morphology, we proposethree different CPs with similar chemical structures but differentmiscibility with Y6. After selectively removing Y6 from the CP/Y6blend films, their interface morphology and interlocked dimensionsare quantitatively compared using a square-wave model. As CP-Y6miscibility increases, a higher intermixed interface is formed, providingan enlarged CP-Y6 interface area. Conversely, as the miscibilitybetween CP and Y6 decreases, the height and width of the interlockeddimensions formed by phase separation gradually decrease and increase,respectively. Additionally, when the CP-Y6 interface morphologyand electrical properties of the corresponding organic photovoltaic(OPV) device are correlated, as the highly intermixed CP-Y6interface develops, the exciton dissociation efficiency increasesowing to the reduced exciton diffusion length to be dissociated, butthe bimolecular recombination tends to deteriorate simultaneously.Furthermore, if the miscibility between CP and Y6 is excessive, theformation of a charge transport pathway through phase separation isinterrupted, deteriorating the charge transport capability in BHJ-typeOPVs. However, it was confirmed that introducing F atoms into theconjugated backbone of CP can reduce the bimolecular recombination,providing ameliorated light-harvesting efficiency.