High-Performance Inverted Organic Photovoltaics Without Hole-Selective Contact

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Inverted organic photovoltaics (OPVs) often require a hole-transporting layer (HTL) for optimal performance.
• Bare silver (Ag) contacts are explored as a potential alternative top electrode in OPVs.

Purpose of the Study:

• To investigate the functionality of inverted OPVs utilizing bare Ag top electrodes without an HTL.
• To understand the role of ambient exposure and oxygen in device performance.

Main Methods:

• Fabrication of inverted OPVs with ITO-ZnO-P3HT/PCBM-Ag structure.
• Exposure of devices to ambient conditions for varying durations.
• Performance characterization including power conversion efficiency (PCE) measurements.
• Accelerated stability testing under damp heat conditions (85% RH, 65 °C).

Main Results:

• HTL-free inverted OPVs show improved hole-carrier selectivity and PCE after ambient air exposure.
• Devices exposed for over 4 days achieved over 3.5% PCE.
• Oxygen presence is critical for achieving fully operational HTL-free devices.
• Bare Ag top electrodes are compatible with various polymer-fullerene systems, reaching 6.5% PCE.
• HTL-free inverted OPVs demonstrated comparable stability to reference devices under damp heat.

Conclusions:

• Bare Ag top electrodes are viable for HTL-free inverted OPVs.
• Ambient air exposure, specifically oxygen, is crucial for activating these devices.
• HTL-free inverted OPVs offer promising efficiency and stability for organic solar cell applications.