A Top-Down Strategy to Engineer ActiveLayer Morphology for Highly Efficient and Stable All-Polymer Solar Cells

Authors：Fu, Huiting; Peng, Zhengxing; Fan, Qunping; Lin, Francis R.; Qi, Feng; Ran, Yixin; Wu, Ziang; Fan, Baobing; Jiang, Kui; Woo, Han Young; Lu, Guanghao; Ade, Harald^*; Jen, Alex K-Y^*

Source：Advanced Materials, 2022, 34(33): 2202608.

DOI：10.1002/adma.202202608

• all-polymer solar cells
• blend morphology
• device stability
• layer-by-layer deposition
• power conversion efficiency

A major challenge hindering the further development of all-polymer solar cells (all-PSCs) employing polymerized small-molecule acceptors is the relatively low fill factor (FF) due to the difficulty in controlling the active-layer morphology. The issues typically arise from oversized phase separation resulting from the thermodynamically unfavorable mixing between two macromolecular species, and disordered molecular orientation/packing of highly anisotropic polymer chains. Herein, a facile top-down controlling strategy to engineer the morphology of all-polymer blends is developed by leveraging the layer-by-layer (LBL) deposition. Optimal intermixing of polymer components can be achieved in the two-step process by tuning the bottom-layer polymer swelling during top-layer deposition. Consequently, both the molecular orientation/packing of the bottom layer and the molecular ordering of the top layer can be optimized with a suitable top-layer processing solvent. A favorable morphology with gradient vertical composition distribution for efficient charge transport and extraction is therefore realized, affording a high all-PSC efficiency of 17.0% with a FF of 76.1%. The derived devices also possess excellent long-term thermal stability and can retain >90% of their initial efficiencies after being annealed at 65 degrees C for 1300 h. These results validate the distinct advantages of employing an LBL processing protocol to fabricate high-performance all-PSCs.

• Institution
  Xi'an Jiaotong University