New insights into the impact of graphene oxide incorporation on molecular ordering and photophysical properties of PTB7:C70 blends

Nano-fillers have been successfully incorporated in the active layer to enhance the performance of bulk heterojunction (BHJ)-based organic solar cells (OSCs). However, only little information is available on their impact on the molecular ordering of polymers in the BHJ blends. Here, we comprehensively analyze the absorption, photoluminescence (PL), and Raman spectra to understand the effect of incorporation of the graphene oxide (GO) nano-filler in PTB7:C70 blends on the molecular ordering of PTB7 polymer. Absorption spectroscopy unveils how the interplay between interchain and intrachain coupling modifies the molecular order and backbone characteristic of PTB7. The addition of C70 weakens both intrachain and interchain interaction of PTB7. Whereas, intrachain interaction gradually rises with increasing the GO concentration. PTB7 films show weakly interacting J-aggregate behavior; nevertheless, the interaction strength gradually improves with the increasing GO content. The PL analysis indicates well-segregated phase domains and enhanced molecular ordering for composite films with 1 wt% GO. The Raman spectra of PTB7:C70:GO composite films suggests the formation of highly ordered PTB7 aggregates. An in-depth understanding of how these properties of polymer blends change with the GO concentration has significant implications on exploiting them towards the development of electronic devices.