Tabulated values of the Shockley–Queisser limit for single junction solar cells

Nanostructured materials for solar energy conversion

Note: EPFL Reference LESO-PB-CONF-2003-017 Record created on 2005-01-12, modified on 2016-08-08

The use of quantum dots can turn the old concept of a luminescent solar collector into a practical concentrator. The quantum efficiency, tunability of absorption threshold, and size of the redshift make quantum dots an ideal replacement for the organic dyes whose performance limited this inexpensive technology. Progress in photovoltaic cells, in particular, the ability of quantum-well cells to tune the band gap, also suggests high efficiency is possible in solar and thermophotovoltaic applications. A thermodynamic model is used to show quantitatively how the separation of absorption and luminescent peaks under global illumination is related to the spread of quantum-dot sizes. Hence, the redshift can be determined during the growth process. The model can be used to optimize concentrator performance and to study the effect of reabsorption, which is important for high concentration even if the quantum efficiency is unity. This model provides a quantitative explanation for the contribution of the spread of sizes to the redshift, which should help in the extraction of the much smaller, single-dot effects.

Quantum-dot concentrator and thermodynamic model for the global redshift

A strain-balance multiquantum well (MQW) approach to enhance the GaAs solar cell efficiency is reported. Using a p-i-n diode structure, the strain-balanced GaAsP/InGaAs MQW is grown on a GaAs substrate and equals a good GaAs cell in terms of power conversion efficiency. The cell design is presented together with measurements of the forward bias dark current density, quantum efficiency, and 3000 K light-IV response. Cell efficiencies under standard air mass (AM) 1.5 and AM 0 illumination are projected from experimental data and the suitability of this cell for enhancing GaInP/GaAs tandem cell efficiencies is discussed.

Strain-balanced GaAsP/InGaAs quantum well solar cells

Quantum well solar cells

It is known that quantum well solar cells (QWSCs) can enhance short circuit current and power conversion efficiency in comparison with similar, conventional solar cells made from the quantum well (QW) barrier material alone. In this article we report measurements of the dark‐current and open‐circuit voltage (Voc) of a number of quantum well cells in three different lattice‐matched material systems, namely, Al0.35Ga0.65As/GaAs, GaInP/GaAs, and InP/InGaAs. We also present the results obtained from comparable control cells without wells formed either from the material of the barriers or the well material alone. Our results clearly demonstrate in all three cases that, at fixed voltage, QWSC dark currents are systematically lower than would be expected from control cells with the same effective absorption edge. Measurements of Voc in a white‐light source show that the open‐circuit voltages of the QWSCs are higher than those of control cells formed from the well material. Furthermore, this enhancement is more t...

Voltage enhancement in quantum well solar cells

Carrier escape from InP/AlGaAs single quantum well structures is studied by means of simultaneous steady state photocurrent and photoluminescence measurements. The activation energy for escape is measured for the first time in this system. The photoluminescence from the InGaAs wells indicates that a significant number of carriers do not escape at room temperature thus affecting the temperature dependence of the cell. An estimate of the nonradiative efficiency of the device studied is given as a function of bias and temperature. The relevance to new applications is discussed.

A carrier escape study from InP/InGaAs single quantum well solar cells

The application of quantum well solar cells to thermophotovoltaics

The authors report on lattice matched InP/In/sub x/Ga/sub 1-x/As multiple quantum well solar cells (QWSCs). An alternative method of p-doping is used, which allows the dopant to diffuse from a highly doped InGaAs cap into an underlying InP layer which has no deliberate doping. They discuss an important experimental technique, the measurement of the monochromatic photocurrent as a function of bias, used to test this approach to p-doping of InP. A model has been developed and theoretical fits of the spectral response (SR) of several multiple quantum well (MQW) samples are shown. They present results that show the enhancement of the short-circuit current (I/sub SC/) over a comparable InP cell and the enhancement of the open-circuit voltage (V/sub OC/) over an InP/InGaAs double heterostructure. This is the first observation of QWSC efficiency enhancement over comparable conventional solar cells made from the well material alone.

Alexander Zachariou

Papers

Quantum well solar cells

Voltage enhancement in quantum well solar cells

A carrier escape study from InP/InGaAs single quantum well solar cells

The application of quantum well solar cells to thermophotovoltaics

A new approach to p-doping and the observation of efficiency enhancement in InP/InGaAs quantum well solar cells