Coupled 2D quantum dot films for next generation solar cells: electronic structure and anomalous light absorption...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology
• Renewable Energy

Background:

• Increasing interest in fabricating high-dimensionality colloidal quantum dot (CQD) arrays for advanced solar cell applications.
• Challenges remain in synthesizing CQD super-solids with reduced inter-dot distances and long-range order.
• Potential applications in hot carrier solar cells and intermediate band solar cells.

Purpose of the Study:

• Investigate the electronic structure and optical absorption of 2D InX (X = P, As, Sb) CQD arrays.
• Understand the dependence of absorption on dot material, number of layers, and interlayer distance.
• Evaluate the feasibility of 3D super-solids for enhancing optical absorption in solar cells.

Main Methods:

• Combined atomistic semi-empirical pseudopotential method for single-dot calculations.
• Tight-binding formalism for array calculations of stacked 2D CQD films.
• Analysis of electronic structure and optical absorption spectra.

Main Results:

• Confirmed universal absorption behavior in 2D materials (0.5-1.2 eV) independent of photon energy, as observed in graphene and InAs nanomembranes.
• Demonstrated that absorbance of stacked layers (A(n)) does not scale linearly with the number of layers (n), i.e., A(n) < nA(1).
• Identified inter-layer coupling as a factor degrading absorption properties in stacked CQD arrays.

Conclusions:

• Achieving 3D super-solids may not improve optical absorption due to inter-layer coupling effects.
• Findings question the strategy of increasing layer count for enhanced absorption in CQD solar cells.
• Proposed a simplified model for intermediate band structure, beneficial for device simulations.