Chemical Modification of n-Type-Material Naphthalene Diimide on ITO for Efficient and Stable Inverted Polymer Solar...

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Bulk-heterojunction polymer solar cells (PSCs) require stable and efficient cathode interlayers (CILs).
• Traditional CILs often face challenges with solvent compatibility and device stability.
• Improving the work function of Indium Tin Oxide (ITO) is crucial for efficient charge extraction.

Purpose of the Study:

• To develop an orthogonal solvent-processable surface modification for ITO.
• To enhance the device stability of PSCs through chemical bonding.
• To improve the power conversion efficiency (PCE) of inverted PSCs.

Main Methods:

• Chemically introduced n-type semiconducting naphthalene diimide (NDI) onto the ITO surface using 3-bromopropyltrimethoxysilane (BrTMS) as a coupling agent.
• Characterized the work function of the modified ITO surface.
• Fabricated inverted PSCs based on PTB7-Th:PC71BM using the modified ITO as a cathode interlayer.

Main Results:

• Reduced the work function of ITO from 4.70 eV to 4.23 eV after NDI modification.
• Achieved a champion power conversion efficiency (PCE) of 5.87% in modified devices, a significant improvement over unmodified devices (3.58%).
• Demonstrated greatly enhanced stability of inverted PSCs due to the chemically bonded interlayers.

Conclusions:

• Chemical modification of ITO with NDI provides a solvent-orthogonal solution for surface modification.
• The NDI-based CIL significantly improves both the PCE and operational stability of PSCs.
• Robust chemical bonds formed in NDI-TMS films contribute to enhanced device longevity and performance.