High-efficiency hybrid planar/bulk heterojunction organic solar cells

An ideal organic solar cell (OSC) should feature both a high donor/acceptor (D/A) interfacial area and a vertically phase-separated architecture. A high interfacial area facilitates exciton diffusion and dissociation into free charges, while vertical phase separation ensures efficient charge transport and collection at the electrodes. Traditional bulk heterojunctions (BHJs) offer a large D/A interfacial area but often lack adequate vertical phase separation. Conversely, quasi-planar heterojunctions (QPHJs) achieve vertical phase separation at the expense of limited D/A interfacial contact area, both of which impede device performance optimization. In this study, we introduce an in situ pore-forming strategy for polymer thin films. By incorporating an excess of additives as pore-forming agents into the donor layer, a nanoporous film with a fibrous nano-network structure is generated. The subsequent deposition of acceptor molecules fills these nanopores, creating a hybrid planar/bulk heterojunction (HP/BHJ) that synergizes the strengths of both quasi-planar and bulk heterojunctions. This innovative architecture attains performance enhancements through the following mechanisms: The nanopores induced by the pore-forming agents substantially augment the interfacial contact area, forming a three-dimensional D/A interfacial network that accelerates exciton dissociation; The close packing of molecular chains facilitated by the pore-forming agents minimizes carrier recombination and establishes low-defect charge transport channels, ensuring efficient vertical charge transport. Additionally, the layer-by-layer deposition approach fosters vertical phase separation, further promoting efficient charge transport. Binary OSCs fabricated using this strategy achieve a remarkable power conversion efficiency (PCE) of 20.0%, surpassing the efficiencies of conventional BHJ and QPHJ devices by a significant margin.