Tuning Acceptor Composition in Ternary Organic Photovoltaics–Impact of Domain Purity on Non-Radiative Voltage Losses

Exaggerated charge losses from excited to charge transfer (CT) and ground states in bulk heterojunction (BHJ) structures results in small voltages (< 1 V) for organic solar cells (OSCs). Characterizing morphology-voltage loss correlations is difficult due to the complexity of BHJ structures but promises the realization of 20% efficiency for OSCs. By utilizing two similar non-fullerene acceptors (NFA) in a ternary blend, a pseudo-binary system is constructed to control the acceptor composition and donor-acceptor (D-A) miscibility. Within the framework of miscibility-morphology controlled device photovoltaics, it is found that higher D-A miscibility results in enhanced domain purity, which is associated with inefficient excitons dissociation and improves the excited and CT state emission, thereby resulting in enhanced electroluminescence efficiency to reduce the non-radiative (NR) loss contribution to device voltage. The simple but effective composition mediated morphology control identifies domain purity as one key feature to lower the NR recombination in high quantum yield polymer/NFA blends.