Additive-Induced Vertical Component Distribution Enables High-Performance Sequentially Cast Organic Solar Cells

Modulation of the active layer morphology to form a vertical component distribution structure is an effective way of improving the efficiency of organic solar cells (OSCs). In this paper, a layer-by-layer (LbL) spin-coating method was adopted combined with an additive strategy to achieve the purpose of precisely adjusting the morphology, and finally, high-performance OSCs based on a D18-Cl/Y6 system were achieved. After adding n-octane in D18-Cl, D18-Cl+/Y6 devices realized a PCE of 17.70%, while with the incorporation of 1-fluoronaphthalene (FN) in Y6, D18-Cl/Y6+ devices obtained a power conversion efficiency (PCE) of 17.39%, both higher than the control devices (16.66%). The former resulted in a more orderly arrangement of D18-Cl, forming a suitable phase separation morphology, and the latter improved the crystallization of Y6, which facilitated carrier transport. Furthermore, the dual-additive-treated D18-Cl+/Y6+ bilayer devices with n-octane doping in the donor and FN in the acceptor had a more desirable vertical morphology, exhibiting an excellent PCE of 18.16% with an improved J_SC of 27.17 mA cm^-2 and FF of 76.88%, one of the highest efficiencies for LbL OSCs. The results demonstrated that combining the LbL spin-coating method with the additive strategy is a valid way to achieve hierarchical morphology control and enhance device performance, which is of great significance for the fabrication and development of OSCs.