5-nm LiF as an Efficient Cathode Buffer Layer in Polymer Solar Cells Through Simply Introducing a C₆₀ Interlayer.

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Lithium fluoride (LiF) is a common cathode buffer layer (CBL) in polymer solar cells (PSCs).
• Standard LiF layer thickness is limited to 1 nm due to its insulating properties, posing challenges in precise deposition and active layer protection.
• Thicker LiF layers are desirable for improved device stability but typically lead to reduced performance.

Purpose of the Study:

• To investigate the application of a thick LiF layer as a CBL in PSCs without compromising device efficiency.
• To explore the use of a C60/LiF bilayer as an alternative to single LiF layers for improved performance and thickness tolerance.

Main Methods:

• Fabrication of bulk heterojunction polymer solar cells (PSCs) utilizing different cathode buffer layer configurations.
• Implementation of a C60 interlayer between the active layer and the LiF layer.
• Characterization of device performance, including power conversion efficiency (PCE), short-circuit current density (Jsc), and photovoltaic properties with varying LiF thicknesses (5 nm and 8 nm).

Main Results:

• Devices with a 5 nm C60/LiF bilayer achieved a peak power conversion efficiency (PCE) of 3.65%, more than double that of a 5 nm LiF-only device (1.79%).
• The enhanced performance is attributed to the improved electrical conductivity of the C60/LiF bilayer due to intermixing at the interface.
• A C60/LiF bilayer device with 8 nm LiF still showed significant PCE (1.10%), whereas a LiF-only device exhibited negligible performance.

Conclusions:

• The C60/LiF bilayer serves as a highly effective cathode buffer layer in PSCs, enabling the use of significantly thicker LiF layers.
• This bilayer structure overcomes the limitations of single LiF layers, offering better device protection and improved efficiency.
• The C60/LiF bilayer is a promising alternative for PSCs, demonstrating high tolerance to variations in LiF thickness.