Two-Photon Sub-Bandgap Photocurrent in Surface-Nanotextured Black Diamond Films for Solar Energy Conversion

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Black diamond films are promising for solar energy conversion.
• Intermediate-band solar cells require specific defect engineering for enhanced performance.
• Two-photon absorption enables sub-bandgap light utilization.

Purpose of the Study:

• To demonstrate two-photon sub-bandgap photocurrent (TPPC) in black diamond films.
• To investigate the role of deep-level defects in enhancing photovoltaic performance.
• To provide a physical interpretation for defect-engineered black diamond solar devices.

Main Methods:

• Fabrication of surface-nanotextured black diamond films using a two-step femtosecond laser treatment.
• Optimization of laser fluence and split ratio for film treatment.
• Sub-bandgap spectral response evaluation (190-1000 nm) to characterize defect levels.

Main Results:

• Successful demonstration of TPPC in black diamond films.
• Observation of a broad intermediate band of electrically active deep-level defects at 1.83 eV from the conduction band.
• Significant enhancement of quantum efficiency under photovoltaic conditions due to the intermediate band.

Conclusions:

• This study presents the first experimental evidence of TPPC in bulk materials with deep-level impurities for intermediate-band solar cells.
• The observed defect band significantly boosts solar energy conversion efficiency.
• The findings offer a solid physical understanding of defect-engineered black diamond solar devices.