An Organic Small Molecule as a Solid Additive in Non-Fullerene Organic Solar Cells with Improved Efficiency and Operational Stability

The use of additive is an effective approach to optimize the active layer morphology and improve the power conversion efficiency (PCE) of organic solar cells (OSCs). However, residual solvent additives always lead to undesirably compromise the stability of OSCs. In this work, an organic small molecule BBT-Cl was designed and used as a novel solid additive to partly replace solvent additive to fabricate highperformance OSCs. The synergistic effect of the dual additives on the optical property, morphology and photovoltaic characteristics of the PM6:Y6 based non-fullerene OSCs have been systematically characterized. The introduction of BBT-Cl could effectively enhance the crystallinity of the blend and promote charge extraction and transport. Consequently, the OSCs processed by the dual additives exhibit a high PCE of 17.73%, which is obviously higher than OSCs with CN additive (16.48%). Meanwhile, BBT-Cl based dual additives treatment has also been successfully introduced into another two non-fullerene OSCs to verify its general applicability. Furthermore, 20% PCE aging is significantly prolonged from 720 min to 2880 min for the devices proceeded with the dual additives. This work highlights the great potential of solid additive in the fabrication of efficient OSCs with excellent stability.