研究目的

Investigating the impact of donor–acceptor interaction and solvent additive on the vertical composition distribution of bulk-heterojunction polymer solar cells.

研究成果

The vertical composition distribution of three model BHJ systems was characterized by NR technique. The investigation results show that donors with lower surface free energy accumulate at the air-film side while acceptors with higher surface free energy accumulate at the film-substrate sides in the ‘as-spun’ BHJ films. PBDB-T:N2200 with strong donor-acceptor interaction presented relatively evenly distributed donor/acceptor blend throughout the BHJ film in vertical direction. While for PBDB-T:PCBM with weak donor-acceptor interaction, the vertical composition distribution across the entire BHJ films shows the strongest inhomogeneity. The vertical segregation effect is enhanced in DIO processed BHJ films, which is partly from the long-time for DIO volatilization, molecules’ migration, films drying process, and formation of more stable BHJ films with low surface free energy. In inverted BHJ solar cells processed with DIO, photovoltaic performance along with charge transport, collection characteristics were simultaneously improved, while charge recombination was suppressed, which could be correlated to the DIO induced vertical morphology ― PBDB-T donor rich region near the anode and acceptor rich region close to the cathode.

研究不足

The study focuses on the vertical composition distribution of BHJ films and its impact on photovoltaic performance, but does not extensively explore the horizontal nanoscale morphology or the detailed mechanisms of charge transport and recombination.