Limiting phase separation via halogen-free solvent slot-die processing enables highly efficient and eco-friendly all-polymer solar cells

Abstract

Developing slot-die coated efficient all-polymer solar cells (all-PSCs) using eco-friendly solvents is extremely crucial for further large-scale production. However, how to gain control over the balanced phase separation and polymer crystallinity to optimize charge dissociation and transport in slot-die coated all-PSCs, is still mysterious and remains challenging. Herein, we report a simple yet efficient strategy to limit phase separation by using halogen-free solvent ortho-xylene (o-XY) at a precisely manipulated solution temperature to enhance the crystallinity of a PBDB-T:PZT-γ blend film. Consequently, this hot slot-die coated all-PSC achieved a record-high power conversion efficiency (PCE) of 15.01% in ambient air without extra processing treatments. Various characterization studies revealed that elevated temperature could appropriately inhibit the aggregation of polymers in o-XY and more free molecular segments obviously promoted the strong crystallization and pure phase, thus leading to a greatly enhanced short-circuit current density and fill factor. Comparatively, the aggregation of PBDB-T in high-temperature halogenated solvent (CB) is overly suppressed, which led to the excessively pure and large phases, and consequently lower PCE. Our effectively integrated strategy can simultaneously optimize the phase separation and crystalline properties by using halogen-free solvent, both of which play significant roles in realizing highly efficient all-PSCs when using the slot-die printing technique.