Green‐Solvent‐Processed Inverted Layer‐by‐Layer Organic Solar Cells Enabled by an Aqueous Soluble Thiophene‐ alt ‐Quinoxaline Donor Polymer

Efficient organic solar cells (OSCs) traditionally rely on bulk heterojunction structures due to the limited exciton diffusion lengths (L D ). The evolution of materials with extended L D , such as the appearance of nonfullerene acceptors (NFAs), enables sequential layer‐by‐layer (LbL) processing of electron donor (D) and acceptor (A) a promising strategy for better control over the morphologies of active layers with configuration of D/A in OSCs. However, its application in an inverted structure, that is A/D, remains underexplored, primarily due to the inadequate solvent resistance of small‐molecule NFAs, which are prone to dissolved during the solution deposition of the D layer. In this work, we report a fully orthogonal, green‐solvent‐based LbL strategy for fabricating inverted OSCs using small‐molecule NFAs. By pairing a water/ethanol‐soluble thiophene‐ alt ‐quinoxaline‐based donor polymer, P(Qx8O‐T), with an o ‐xylene‐processed acceptor, L8‐BO, we successfully suppressed interlayer dissolution, allowing intact deposition of the donor layer without damaging the underlying acceptor film. Furthermore, this strategy effectively maintains the intrinsic crystallization of the donor and NFA layers, resulting in high‐quality active layers with well‐defined vertical phase separation. Consequently, the green‐solvent‐processed inverted LbL devices achieve a power conversion efficiency of 5.88%, demonstrating the feasibility of OSCs as a green PV technology.