Vertically Processed GaInP/InP Tandem-Junction Nanowire Solar Cells.

Area of Science:

• Materials Science
• Nanotechnology
• Renewable Energy

Background:

• III-V nanowires (NWs) offer potential for advanced photovoltaic applications.
• Tandem-junction solar cells enhance efficiency by utilizing a broader solar spectrum.
• Vertical processing enables parallel contacting of numerous nanowires for improved device fabrication.

Purpose of the Study:

• To investigate the effect of GaInP composition on GaInP/InP tandem-junction nanowire solar cell performance.
• To optimize device parameters for enhanced solar energy conversion.
• To identify limitations and suggest improvements for high-efficiency nanowire photovoltaics.

Main Methods:

• Fabrication of vertically processed GaInP/InP tandem-junction III-V nanowire solar cells.
• Systematic variation of the GaInP top junction material composition.
• Characterization using external quantum efficiency (EQE) and current-voltage (I-V) measurements under AM1.5G illumination.

Main Results:

• Devices contacted approximately 3 million nanowires in parallel.
• GaInP and InP subcells, along with the Esaki tunnel diode, were integrated within a single nanowire.
• EQE measurements indicated the GaInP subcell was current-limiting across all devices.
• I-V measurements confirmed subcell voltage addition, achieving an open-circuit voltage up to 1.91 V.
• Short-circuit current density ranged from 0.24 to 3.44 mA/cm², resulting in a maximum solar conversion efficiency of 3.60%.

Conclusions:

• Optimizing GaInP composition is crucial for tandem-junction nanowire solar cell performance.
• The GaInP subcell currently limits the overall current density and efficiency.
• Further improvements are needed to overcome current limitations and advance nanowire photovoltaics.