Directed Vertical Diffusion of Photovoltaic Active Layer Components into Porous ZnO-Based Cathode Buffer Layers

Area of Science:

• Materials Science
• Energy Science
• Nanotechnology

Background:

• Cathode buffer layers (CBLs) are crucial for polymer solar cell (PSC) efficiency.
• Vertical diffusion of active layer components into the CBL is a critical, understudied factor.

Purpose of the Study:

• To develop a novel method for mapping multicomponent depth composition in inverted PSCs.
• To investigate the porosity and diffusion dynamics within ZnO-based CBLs.

Main Methods:

• Utilized contrast variation with neutron and anomalous X-ray reflectivity.
• Analyzed depth composition from the active layer surface to the ZnO-based CBL base.
• Investigated diffusion of polymer PTB7-Th and fullerene derivative PC71BM.

Main Results:

• Revealed porosity distributions in ZnO-based CBLs.
• Quantified differential diffusion of polymer and fullerene components into the CBL.
• Demonstrated that PCBE-OH modification of CBL creates selective nanochannels, enhancing PC71BM diffusion.

Conclusions:

• Interface modification of CBLs with fullerene derivatives can improve electron mobility and PSC efficiency.
• A gradient distribution of fullerene derivatives over the CBL enhances device performance.
• Proposed a new CBL design strategy based on progressive conduction band matching.