III–V Multi-junction Solar Cells

Abstract

III–V compound semiconductors consist of elements out of the main groups III and V of the periodic table. Through proper mixing of the elements, materials with a wide range of bandgaps are available and can be realized in excellent crystal quality. The highest efficiencies of any photovoltaic technology, so far, have been reached with solar cells consisting of such III–V compound semiconductors. This is in particular enabled by stacking solar cells of several III–V compound semiconductors, which absorb different parts of the solar spectrum. These III–V multi-junction solar cells have become standard in space and in terrestrial concentrator systems. The variety of materials as well as an extensive technological toolbox has already led to the realization of diverse solar cell architectures. The current landmark is the Ga0.50In0.50P/Ga0.99In0.01As/Ge triple junction, which only contains lattice-matched layers. This MOVPE-grown device has achieved a record efficiency of 41.6% and is commercially available with efficiencies around 40% under concentrated sunlight. Due to the mature development status of this device new concepts are being investigated to increase the efficiencies further. Methods in the technological toolbox have been used and combined intensively in recent years to realize material combinations, which allow a more efficient use of the solar spectrum. Several approaches have already reached efficiencies higher than the lattice-matched triple-junction solar cell. The aim of this chapter is to give an introductory overview of III–V multi-junction solar cells with a special emphasis on the origins of high efficiencies, the technological toolbox and some exemplary solar cell architectures. Innovative ideas and methods such as metamorphic and inverted growth, wafer-bonding, different substrates, nanostructures, different growth technologies and new materials are discussed.

Component cell–based restriction of spectral conditions and the impact on CPV module power rating

“…The specimens investigated in this work are lattice‐matched (LM3J), upright metamorphic (UMM3J), and inverted metamorphic triple‐junction (IMM3J) solar cells as well as 4‐junction (4J) solar cells. These cells cover most of the current state‐of‐the‐art for multijunction solar cells and have proven their high potential in efficiency . Table lists the band gap energy and the excess current of the subcells calculated for AM1.5d spectral conditions.…”

“…Different multijunction cell concepts with efficiencies above 40% are industrially available and even more cell concepts are under development in different laboratories. Philipps and Bett list the most important III‐V cell concepts . All multijunction concepts have in common that they have a higher sensitivity to spectral conditions compared to single‐junction cells.…”

Automated design of multi junction solar cells by genetic approach: Reaching the >50% efficiency target

“…However, this concept still lacks the detailed theoretical descriptions and understanding of major factors influencing the operation and efficiency of such devices. The majority of MJSC models so far were based on principles of the detailed balance and thermodynamics [4] [5] [6] [7], with recent attempts to address the real SC's material parameters [8] The main conceptual message of the MJSC and a route to overcome the poor spectral matching of a single-junction SC is to introduce subcells with different energy gaps (E g ) into the device [9]. Such devices consisting of several solar cells (SC), i.e subcells, each of which with different E g are capable of absorbing the photons from different part of the solar spectrum.…”

GaInP/AlGaAs metal‐wrap‐through tandem concentrator solar cells

“…The highest light‐to‐electricity conversion efficiencies are achieved with photovoltaic devices made of III–V semiconductor materials. For this reason, they are the candidate of choice for many high‐performance applications such as satellite power generation, high‐concentration photovoltaics (PV) and optical power transmission . Four‐junction solar cells with a record efficiency of 46.1% (at 312xAM1.5d) have been demonstrated by using wafer bonding, and several other device architectures have also been suggested , including inverted four‐junction solar cells which have reached efficiencies up to 45.6% (at 690xAM1.5d) .…”