Temperature-guided solidification of copper coordination complexes as hole transport materials

Area of Science:

• Materials Science
• Photovoltaics
• Electrochemistry

Background:

• Dye-sensitized solar cells (DSCs) require efficient hole-transport materials (HTMs) for optimal performance.
• Traditional fabrication of copper-based HTMs in DSCs is time-consuming, often exceeding 48 hours.
• Developing rapid, controllable solid-state formation processes for HTMs is crucial for commercial viability.

Purpose of the Study:

• To establish a rapid, solid-state formation process for copper coordination complex HTMs in DSCs.
• To investigate the effect of post-treatment conditions on HTM morphology and photovoltaic performance.
• To optimize interfacial charge transfer and device efficiency, particularly under low-light conditions.

Main Methods:

• Utilized thermally-induced phase transition of Cu(I/II)(tmby)2-based liquid electrolytes.
• Employed a 70 °C post-treatment for 20 minutes to form amorphous HTMs.
• Characterized HTM morphology using scanning electron microscopy and solvent removal via time-dependent Raman spectroscopy.
• Analyzed charge carrier dynamics using transient absorption spectroscopy and interfacial properties with electrochemical impedance spectroscopy.

Main Results:

• Reduced HTM processing time from over 48 hours to 20 minutes.
• Achieved near-complete solvent removal and a compact, defect-minimized HTM morphology.
• Demonstrated ultrafast dye regeneration (487 ns) and high regeneration efficiency (99.2%) with short heat treatments.
• Observed stable charge-transfer resistances at the TiO2/HTM interface, confirming efficient hole transport.
• Attained up to 10% power conversion efficiency under 1 sun and 16% peak efficiency under indoor lighting (1000 lux).

Conclusions:

• A robust and reproducible solid-state route for fabricating Cu-based HTMs in DSCs was established.
• Optimized post-treatment conditions (70 °C for 20 min) yield superior HTM morphology and device performance.
• The process enhances low-light performance and photovoltaic yield by controlling morphology and interfacial charge transfer.