Chemically Passivated Polymeric Charge Recombination Layer for Efficient Tandem Organic Solar Cells

Tandem organic solar cells (TOSCs) offer a promising route to surpassing the efficiency limits of single‐junction devices, yet their performance remains constrained by interfacial losses at the charge recombination layer (CRL). Here, we report a chemically passivated polymeric CRL based on spontaneous in situ protonation‐induced ionic self‐assembly of amine‐rich polyelectrolytes on PEDOT:PSS. This process forms a robust dipole layer that significantly reduces the work function of PEDOT:PSS, creating a favorable energetic alignment for charge recombination. Notably, temperature‐dependent current‐voltage analysis provides quantitative insight into interfacial energetics, revealing a near‐zero or even negative effective barrier height (Φ B ≈ −28 meV) at the polymeric CRL interface. This result, which signifies a nearly ideal ohmic contact, stands in contrast to the substantial energy barrier (Φ B ≈ 33 meV) that impedes charge transport in conventional ZnO‐based CRLs. As a result of the barrier‐free recombination, homojunction TOSCs incorporating polymeric CRL yield a power conversion efficiency of over 18%, outperforming their ZnO‐based counterparts. This work presents a versatile and scalable interfacial engineering strategy that harnesses in‐situ chemical reactions to concurrently stabilize interfaces and tailor electronic properties, providing an effective pathway toward high‐performance, reliable TOSCs.