A Review of Ultrahigh Efficiency III-V Semiconductor Compound Solar Cells: Multijunction Tandem, Lower Dimensional, Photonic Up/Down Conversion and Plasmonic Nanometallic Structures

Katsuaki Tanabe

doi:10.3390/en20300504

Abstract

Solar cells are a promising renewable, carbon-free electric energy resource to address the fossil fuel shortage and global warming. Energy conversion efficiencies around 40% have been recently achieved in laboratories using III-V semiconductor compounds as photovoltaic materials. This article reviews the efforts and accomplishments made for higher efficiency III-V semiconductor compound solar cells, specifically with multijunction tandem, lower-dimensional, photonic up/down conversion, and plasmonic metallic structures. Technological strategies for further performance improvement from the most efficient (Al)InGaP/(In)GaAs/Ge triple-junction cells including the search for 1.0 eV bandgap semiconductors are discussed. Lower-dimensional systems such as quantum well and dot structures are being intensively studied to realize multiple exciton generation and multiple photon absorption to break the conventional efficiency limit. Implementation of plasmonic metallic nanostructures manipulating photonic energy flow directions to enhance sunlight absorption in thin photovoltaic semiconductor materials is also emerging.

Highlights

The current world consumption of electric energy is around 12–13 TW and the earth receives more solar energy in one hour than the energy used globally in one year, considering the solar constant1.7 × 105 TW at the top of the earth’s atmosphere [1]
Electron–hole pairs are generated by the energy of the incident photons overcoming the energy bandgap of the photovoltaic material to make a current flow according to the built-in potential slope in the material
The energy conversion efficiency of a solar cell is defined as the ratio of the electric power generated by the solar cell to the incident sunlight energy into the solar cell per time

Summary

Introduction

The current world consumption of electric energy is around 12–13 TW and the earth receives more solar energy in one hour than the energy used globally in one year, considering the solar constant. The energy conversion efficiency of a solar cell is defined as the ratio of the electric power generated by the solar cell to the incident sunlight energy into the solar cell per time. We focus on solar cells made of III-V semiconductor compounds since these types of solar cells have exhibited the leading energy conversion efficiencies, rather than the other materials represented by silicon [9]. Besides the potential for high efficiency, III-V semiconductor compound materials have advantages including the bandgap tunability by elemental compositions, higher photon absorption by the direct bandgap energies, higher resistivity against high-energy rays in space, and smaller efficiency degradation by heat than Si solar cells. Kazmerski et al at National Renewable Energy Laboratory/National Center for Photovoltaics (as a work of the U.S federal government, the image is in the public domain)

Developments of Multijunction III-V Solar Cells

Utilization of Higher Energy Photons

Utilization of Lower Energy Photons

Plasmonic Nanometallic Structures for Light Absorption Enhancement

Findings

Conclusions