High‐Performance Thick‐Film Organic Solar Cells Based on Layer‐by‐Layer Mutual Doping Strategy

The thickness sensitivity of organic solar cells (OSCs) has become a key challenge for their industrialization. The layer‐by‐layer (LbL) method is used to prepare pseudo‐planar heterojunctions (P‐PHJ), which have advantages in constructing vertical phase separation. In thin‐film P‐PHJ, interlayer permeation can form sufficient D/A interfaces. However, the D/A interface area cannot increase linearly with the thickness of P‐PHJ. This work adopts a ternary LbL mutual doping (LbL‐MD) strategy to fabricate D1 +A /A +D2 active layers, where D18 is the primary donor (D1), D18‐Cl is the secondary donor (D2), and L8‐BO is the acceptor (A). The thickness tolerance of OSCs is significantly improved along with the optimization of the interpenetrating network structure and molecular arrangement. The OSCs based on D1 +A /A +D2 with 160 nm thickness exhibit excellent photoelectric conversion efficiency (PCE) of 20.11%, which is higher than the optimal PCE of 19.09% for the OSCs based on D1/A with 120 nm thickness. When the active layer thickness is 300 nm, the PCE of OSCs based on D1 +A /A +D2 can still reach 18.75%, while the PCE of OSCs based on D1/A is decreased to 17.61%. This study proves that the ternary LbL‐MD strategy is a feasible approach for improving the thickness tolerance of the P‐PHJ OSCs.