Highly Efficient Parallel-Like Ternary Organic Solar Cells

Ternary bulk heterojunction (BHJ) blends have been demonstrated as a promising approach to increase the power conversion efficiencies (PCEs) of organic solar cells. Currently, most studies of ternary organic solar cells are based on blends of two donors and one acceptor, because of the limitation in acceptor materials. Here, we report that high-performance ternary solar cells have been fabricated with a wide-bandgap polymer donor (PDBT-T1) and two acceptor materials, phenyl-C70-butyric acid methyl ester (PC₇₀BM), and nonfullerene acceptor (ITIC-Th). The addition of ITIC-Th into the BHJ blends dramatically increases the light absorption. Consequently, the champion ternary solar cell shows a high PCE of ∼10.5%, with an open-circuit voltage (V_oc) of 0.95 V, a short-circuit current (J_sc) of 15.60 mA/cm², and a fill factor (FF) of 71.1%, which largely outperforms their binary counterparts. Detailed studies reveal that the ternary solar cells work in a parallel-like device model (ITIC-Th and PC₇₀BM form their own independent transport network) when ITIC-Th loading is >30% in the ternary blends. The results indicate that the combination of fullerene derivative and appropriate nonfullerene acceptor in a ternary blend can be a new strategy to fabricate high-performance ternary organic solar cells.