Solar photovoltaic electricity: Current status and future prospects

Solar cell efficiency tables (version 57)

Solar cell efficiency tables (Version 55)

CO2 conversion into value-added chemicals and fuels is considered as one of the great challenges of the 21st century. Due to the limitations of the traditional thermal approaches, several novel technologies are being developed. One promising approach in this field, which has received little attention to date, is plasma technology. Its advantages include mild operating conditions, easy upscaling, and gas activation by energetic electrons instead of heat. This allows thermodynamically difficult reactions, such as CO2 splitting and the dry reformation of methane, to occur with reasonable energy cost. In this review, after exploring the traditional thermal approaches, we have provided a brief overview of the fierce competition between various novel approaches in a quest to find the most effective and efficient CO2 conversion technology. This is needed to critically assess whether plasma technology can be successful in an already crowded arena. The following questions need to be answered in this regard: are there key advantages to using plasma technology over other novel approaches, and if so, what is the flip side to the use of this technology? Can plasma technology be successful on its own, or can synergies be achieved by combining it with other technologies? To answer these specific questions and to evaluate the potentials and limitations of plasma technology in general, this review presents the current state-of-the-art and a critical assessment of plasma-based CO2 conversion, as well as the future challenges for its practical implementation.

/pdf/plasma-technology-a-novel-solution-for-co2-conversion-bxzhxztf2d.pdf

Plasma technology - a novel solution for CO2 conversion?

Solar cell efficiency tables (Version 53)

Triple-junction solar cells from III–V compound semiconductors have thus far delivered the highest solar-electric conversion efficiencies. Increasing the number of junctions generally offers the potential to reach even higher efficiencies, but material quality and the choice of bandgap energies turn out to be even more importance than the number of junctions. Several four-junction solar cell architectures with optimum bandgap combination are found for lattice-mismatched III–V semiconductors as high bandgap materials predominantly possess smaller lattice constant than low bandgap materials. Direct wafer bonding offers a new opportunity to combine such mismatched materials through a permanent, electrically conductive and optically transparent interface. In this work, a GaAs-based top tandem solar cell structure was bonded to an InP-based bottom tandem cell with a difference in lattice constant of 3.7%. The result is a GaInP/GaAs//GaInAsP/GaInAs four-junction solar cell with a new record efficiency of 44.7% at 297-times concentration of the AM1.5d (ASTM G173-03) spectrum. This work demonstrates a successful pathway for reaching highest conversion efficiencies with III–V multi-junction solar cells having four and in the future even more junctions. Copyright © 2014 John Wiley & Sons, Ltd.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pip.2475

Wafer bonded four-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cells with 44.7% efficiency

The highest solar cell conversion efficiencies are achieved with four-junction devices under concentrated sunlight illumination. Different cell architectures are under development, all targeting an ideal bandgap combination close to 1.9, 1.4, 1.0, and 0.7 eV. Wafer bonding is used in this work to combine materials with a significant lattice mismatch. Three cell architectures are presented using the same two top junctions of GaInP/GaAs but different infrared absorbers based on Germanium, GaSb, or GaInAs on InP. The modeled efficiency potential at 500 suns is in the range of 49–54% for all three devices, but the highest efficiency is expected for the InP-based cell. An efficiency of 46% at 508 suns was already measured by AIST in Japan for a GaInP/GaAs//GaInAsP/GaInAs solar cell and represents the highest independently confirmed efficiency today. Solar cells on Ge and GaSb are in the development phase at Fraunhofer ISE, and the first demonstration of functional devices is presented in this paper.

Four-Junction Wafer-Bonded Concentrator Solar Cells

The highest solar cell conversion efficiencies are achieved with Four-junction devices under concentrated sunlight illumination. Different cell architectures are under development, all targeting an ideal bandgap combination close to 1.9 eV, 1.4 eV, 1.0 eV and 0.7 eV. Wafer bonding is used in this work to combine materials with a significant lattice-mismatch. Three cell architectures are presented using the same two top junctions of GaInP/GaAs but different infrared absorbers based on Germanium, GaSb or GaInAs on InP. The modelled efficiency potential at 500 suns is in the range of 49–54 % for all three devices but the highest efficiency is expected for the InP-based cell. An efficiency of 46 % at 508-suns was already measured by AIST in Japan for a GaInP/GaAs//GaInAsP/GaInAs solar cell and represents the highest independently confirmed efficiency today. Solar cells on Ge and GaSb are in the development phase at Fraunhofer ISE and first demonstration of functional devices is presented in this paper.

Four-junction wafer bonded concentrator solar cells

The effect of increasing the number of quantum wells in a strain-compensated, multiquantum-well solar cell is investigated. It is found that as the well number is increased, dark current level close to the operating point rises linearly. Short-circuit current in the AM0 spectrum also rises linearly with the inclusion of more quantum wells. This allows the cell to maintain a constant open-circuit voltage irrespective of the number of wells grown. This is anticipated to have advantages when the cell is used as a replacement for the GaAs junction in the existing generation of tandem and triple-junction cells since current levels can be matched to the upper junction without detriment to the voltage performance. This result allows us to predict a tandem cell AM0 efficiency of 23.8% based on the 50-well cell.

Effect of well number on the performance of quantum-well solar cells

III-V InGaP/InGaAs/Ge triple junction solar cells have been developed which incorporate quantum wells into the InGaAs and InGaP junctions. Characterization of such devices shows an absolute efficiency gain of up to 2% with Voc exceeding that of non-QW devices. Cells grown on 6" wafers with quantum wells in the InGaAs junction are now commercially available with median efficiencies above 41%.

/pdf/triple-junction-quantum-well-solar-cells-in-commercial-2760xrlmld.pdf

T.N.D. Tibbits

Papers

Wafer bonded four-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cells with 44.7% efficiency

Four-Junction Wafer-Bonded Concentrator Solar Cells

Four-junction wafer bonded concentrator solar cells

Effect of well number on the performance of quantum-well solar cells

Triple-junction quantum-well solar cells in commercial production