Controlling intercalations of PBDTTT-EFT side chain to initiate suitable network for charge extraction in PBDTTT-EFT:PC71BM blended bulk heterojunction solar cell

Abstract
Electrical, optical and structural properties, based on blend of PBDTTT-EFT:PC71BM bulk heterojunction solar cell is investigated. We have shown the presence of PC71BM in the blend facilitates interfaces for charge transfer mechanisms leading to PCEs of ~ 9.38%. GIXRD line profile obtained reveals that quantitative presence of PC71BM initiates a change in preferred orientation. It is proposed that PC71BM facilitates polymer alkyl side chain intercalations causing reduced d100 spacing, leading to larger π-π stacking of the back bone. The data obtained from d200 plane associated with PC71BM, reveals correlation between increased vertical stacking and PC71BM loading, suggesting a bicontinuous network for electron transport. Raman spectroscopy results provides evidence of PC71BM impact on frequency shift associated with C = C stretching mode of side chain thiophene rings responsible for of π-π spacing. Correlations between AFM surface roughness and blend ratio reveals migration of PC71BM to the film surface.

Keywords: (copolymer solar cell, power conversion efficiency, side chain intercalations, XRD)