Sequential stacking of a thin BHJ layer acting as a morphology regulator for efficiency enhancement in non-fullerene ternary solar cells

Although ternary-blend solar cells (TSCs) featuring alloyed systems with two acceptors can display high power conversion efficiencies (PCEs) while minimizing energy loss, it can be difficult to control the morphology of the alloyed ternary blend. In this study we developed a gradient ternary (Gradient-Ternary) device architecture by transferring a bulk-heterojunction (BHJ) layer over the spin-coated ternary blend to enhance the PCEs of alloyed TSCs. The Gradient-Ternary architecture, which was similar to that of a compositional-gradient BHJ blend, featured a vertically stratified morphology that established efficient charge extraction pathways, thereby mitigating the recombination loss faced by the corresponding Ternary blend, while concurrently improving the photocurrent, relative to that of the Ternary blend, without suffering losses in any of the other photovoltaic parameters. A champion efficiency of 16.5% was obtained using the Gradient-Ternary architecture (PM6:Y6: ITIC/PM6:ITIC) was higher than those of the Ternary (PM6:Y6:ITIC) and Binary (PM6:Y6) architectures exhibiting an efficiency of 15.7% and 15.0% respectively. Applying such gradient architectures might also accelerate the efficiency of other organic solar cells.

Automated summary

In this study, a gradient ternary device architecture was developed to enhance the power conversion efficiency of alloyed solar cells. The architecture, featuring a vertically stratified morphology, established efficient charge extraction pathways and improved the photocurrent. The results showed that the gradient ternary structure achieved higher efficiency, with a 0.8% and 1.5% improvement compared to the ternary and binary structures respectively.