Upper Layer-Modulated Pseudo Planar Heterojunction with Metal Complex Acceptor for Efficient and Stable Organic Photovoltaics

Modulating self-aggregation and charge transport in the upper acceptor layer of the pseudo planar heterojunction (PPHJ) is crucial for enhancing dielectric constant and suppressing trap density, leading to efficient and stable organic photovoltaics (OPVs). In this work, a metal complex acceptor (MCA), PtAC-Cl, is selectively incorporated into the upper host Y6 layer of PPHJ to regulate morphology and fill trap states. There exists a strong chemical interaction between PtAC-Cl and Y6, which can promote electron transfer. PtAC-Cl can regulate the self-aggregation and extend the exciton diffusion length of Y6, resulting in enhanced charge transport and reduced energetic disorder. Consequently, upper layer-modulated PPHJ devices with PtAC-Cl achieved a significant power conversion efficiency of 18.16%. The universality of PtAC-Cl is also demonstrated in PM6/eC9 and PM6/L8-BO systems, achieving the highest PCEs of 18.79 and 19.30%, respectively. All the improved PCEs are mainly attributed to the enhanced fill factor (FF) and short circuit current (J_sc) compared with the controls. Additionally, PtAC-Cl significantly improves the thermal stability and photostability of the devices, with a T₈₀ lifetime of ≈ 401 h under continuous illumination with simulated 1-Sun light and 1265 h under continuous heating at 70 °C. Overall, this work introduces the concept of MCA and proposes a practical and efficient method to enhance the efficiency and stability of OPVs through selective upper-layer modulation in PPHJ with MCA.