Enhanced Efficiency of Intermediate-Band Semiconductor Solar Cells Embedded with Quantum Dot Superlattices

TL;DR

The work addresses efficiency limits of single-junction solar cells by implementing a quantum dot superlattice–based intermediate band to harvest sub-bandgap photons. It advances a multiscale approach that couples a tight-binding calculation of miniband structure and absorption with experimental valence-to-conduction data, integrated into a COMSOL drift-diffusion model including SRH recombination. The key finding is an optimal QDSL lattice constant of $a = 14$ nm, achieving a maximum efficiency of $\eta = 13.3\%$ and about a $1.7\times$ improvement over a reference Ga$_{0.7}$Al$_{0.3}$As p–n junction without QDSL, while excessively large $a$ reduces performance due to weaker generation in the n-type region. The results demonstrate a physically grounded framework for designing QDSL IBSCs and highlight the value of integrating theory, experiment, and computation for photovoltaic optimization.

Abstract

We present a multiscale approach for modeling an intermediate-band solar cell based on a GaAs-GaAlAs quantum dot superlattice of cubic symmetry. Our framework combines high-accuracy theoretical calculations of the superlattice band structure and miniband-related absorption coefficient with experimentally determined interband absorption data. The quantum-mechanically derived absorption spectrum is incorporated into a drift-diffusion transport model in COMSOL Multiphysics, where key processes, including thermal and radiative recombination, are taken into account. This integrated methodology enables realistic modeling of device performance. Our results identify an optimal superlattice constant of 14 nm, yielding a maximum solar cell efficiency of 13.3 percent. Further increase in the superlattice constant enhances the miniband-related absorption peak but reduces the generation rate in the n-type region, resulting in a net efficiency decrease. The proposed approach, integrating theoretical, experimental, and computational components, provides a reliable framework for assessing solar cells based on quantum dot superlattices.

Figures (6)

• Figure 1: Schematic picture of the $p-n$ junction solar cell embedded with a QD superlattice.
• Figure 2: Band structure of the system versus lattice constant $a$.
• Figure 3: Absorption coefficient versus wavelength for various values of lattice constant $a$. Inset: Absorption coefficient of the bulk Ga$_{0.7}$Al$_{0.3}$As.
• Figure 4: Generation rate versus penetration depth for various values of lattice constant $a$. Dashed line corresponds to the Ga$_{0.7}$Al$_{0.3}$As $p-n$ junction solar cell without QDSL.
• Figure 5: Volt--ampere characteristics for various values of lattice constant $a$. Dashed line corresponds to the Ga$_{0.7}$Al$_{0.3}$As $p-n$ junction solar cell without QDSL.