Achieving 20.8% organic solar cells via additive-assisted layer-by-layer fabrication with bulk p-i-n structure and improved optical management

Additive-assisted layer-by-layer (LBL) deposition affords interpenetrating fibril network active layer morphology with a bulk p-i-n feature and proper vertical segregation in organic solar cells (OSCs). This approach captures the balance between material interaction and crystallization that locks the characteristic length scales at tens of nanometers to suit exciton and carrier diffusion, thereby reducing recombination losses. On the other hand, the wrinkle-pattern morphology generated due to Marangoni-Bénard instability and radial flow during spin-coating couples with the reflective back electrode, inducing diffuse reflection and thus enhancing light capture capability. The nano-to-micron hierarchical morphology in proper vertical segregation achieves a record-breaking power conversion efficiency (PCE) of 20.8% for small-area devices and 17.0% for mini-module devices. The new processing and the resulted 3D morphology better suit photon and carrier dynamics in operation, such that a notable improvement in device operational stability is recorded, which offers a plausible strategy toward practical organic photovoltaic technology.