Highly Efficient and Stable SnO2-Based Inverted Organic Solar Cells Modified with a Simple Small Molecule Exceeding 19% Efficiency

A conventional cathode interlayer (CIL) material commonly employed in organic light-emitting diodes, namely, bathocuproine (BCP), was strategically utilized to functionalize the tin oxide (SnO₂) electron transport layer (ETL) within inverted organic photovoltaic devices. Both theoretical quantum chemical calculations and empirical experimental investigations consistently confirm the existence of interfacial interaction between BCP and tin oxide (SnO₂), effectively reducing the work function of SnO₂, improving its electrical conductivity, and filling some defects on the SnO₂ surface, thereby reducing the charge recombination and enhancing exciton dissociation and charge transport in inverted organic solar cells (OSCs). As results, the power conversion efficiencies (PCEs) based on BCP-modified devices are improved from 15.24% to 16.94% (PM6:Y6) and 18.77% (PM6:L8-BO), and that of the ternary OSCs (D18:L8-BO:BTP-eC9) is even up to 19.13%, which are among the highest efficiencies for inverted OSCs. Additionally, SnO₂/BCP devices show excellent stability (storage stability, light stability, thermal stability, humid stability and UV stability), and in maximum power point tracking tests, the T₈₀ (the lifetime of PCE decay to 80% of its initial efficiency) of SnO₂/BCP devices exceeds 500 h, which is remarkable improvement compared to that of 63 h of SnO₂ devices. The improved PCEs and stability can be mainly ascribed to the passivation of the defects on SnO₂ by BCP due to the interactions between the N atoms of BCP and Sn atoms of SnO₂, and the better contact of SnO₂/BCP ETLs with the active layers also plays positive roles for the enhanced device performance.