Background

Solar cells that replace silicon with light-harvesting polymers and small molecules have the potential to enable to production of light-weight, flexible and semi-transparent solar panels that will revolutionize the way we interact with energy sources. In the laboratory, organic solar cell light conversion efficiencies have recently exceeded 16%, surpassing that of commercial polycrystalline silicon solar panels. However, these laboratory-scale devices are invariably fabricated through an energy-intensive, batch spin coating process. The use of high throughput manufacturing methods is necessary to drive down the cost of organic solar panels and make them commercially viable. To be successful, these large-scale deposition methods need to provide control over the active layer morphology (i.e. extent of crystallization of the components and degree of phase separation between them), which in turn determines the overall solar cell efficiency. 

Leveraging tools of the well-established polymer manufacturing industry, our invention uses twin screw extrusion as a means to continuously deposit high-performance organic solar cell active layers. These active layers typically comprise a blend of a semiconducting polymer and semiconducting small molecule. The extruder is capable of simultaneously cooling, mixing and shearing polymer nanocomposite solutions prior to depositions. We discovered that 1) rapid cooling induces polymer crystallization and gelation in a robust, reproducible manner and 2) shearing induces small-molecule crystallization, with the size of crystals decreasing with increasing shear rate. The ability to form small molecule crystals within polymer matrices is important not only to the solar cell field, but also to myriad industries, from performance materials to pharmaceutics.  

Summary 

We have developed a novel process to continuously deposit organic solar cell photoactive layers comprising polymer/small molecule nanocomposites with morphologies optimized for light energy harvesting. The process uses cooling to induce polymer gel formation via crystallization, while shearing is used to control small molecule nucleation and crystallization. Using a twin-screw extruder to simultaneously cool and shear, this process is compatible with high throughput manufacturing methods required to drive down the cost of organic solar cells.  

Benefits 

Compatible with continuous processing methods

Robust and reliable control over active layer morphology (i.e. polymer crystallization, small molecule crystallization, and extent of phase separation) 

Applications 

Organic solar cells

Organic light emitting diodes

Perovskite solar cells

Pharmaceutical compounds 

Key Words 

Twin-screw extrusion, polymer nanocomposites, organic solar cell, continuous manufacturing, shear-induced crystallization