Origin of Suppressed Photovoltage Loss in Organic Solar Cells With Additive Engineering

Additive engineering has become widely adopted for tuning morphology and photovoltaic behaviors of organic solar cells (OSCs), while the resultant increase in delocalization of charge transfer (CT) excitons is often accompanied by a reduced CT-state energy of additive-processed blend films, which impairs photovoltage and restrains further improvements of photovoltaic efficiencies. Here, we achieve mitigation of photovoltage loss (V_loss) over 30 meV while remaining high charge generation/transport efficiencies in a range of OSCs with A-D-A'-D-A type acceptors after additive treatment. Combined experimental and molecular dynamics simulation analyses reveal that additive treatments suppress voltage loss primarily by increasing the dielectric constant (ε_r) in the CT state and reducing energetic disorder. These changes help inhibit back charge transfer from charge-separated states to CT states, thereby decreasing non-radiative recombination (ΔV_non-rad) and improving device open-circuit voltage. We further establish a universal ε_r-dependent relationship for voltage loss, showing that both the increase in photovoltage and the reduction in ΔV_non-rad scale linearly with the enhancement of the blend dielectric constant. These findings deepen our insights into the voltage loss in organic solar cells, paving a way for surpassing the current photovoltage limits toward higher-performance devices.