A new approach to high-efficiency multi-band-gap solar cells

Abstract

The advantages of using multi-quantum-well or superlattice systems as the absorbers in concentrator solar cells are discussed. By adjusting the quantum-well width, an effective band-gap variation that covers the high-efficiency region of the solar spectrum can be obtained. Higher efficiencies should result from the ability to optimize separately current and voltage generating factors. Suitable structures to ensure good carrier separation and collection and to obtain higher open-circuit voltages are presented using the (AlGa)As/GaAs/(InGa)As system. Efficiencies above existing single-band-gap limits should be achievable, with upper limits in excess of 40%.

Fundamental limits in the external quantum efficiency of single nanowire solar cells

“…Their increasing importance in both science and engineering is a consequence of the great number of fundamental experiments and applications they enable. [1][2][3][4][5][6][7][8] In the recent years, an increasing interest in the use of nanowires for solar cell applications has been observed. 9 The set point for this was the realization that radial nanowire p(i)n junctions offer a significant advantage with respect to the planar counterparts, as they allow to orthogonalize the light absorption with the carrier separation in the device.…”

Design and mechanism of cost-effective and highly efficient ultrathin (< 0.5 μm) GaAs solar cells employing nano/micro-hemisphere surface texturing

“…for multijunction solar cell applications. [5][6][7][8] However, the high cost associated with the material itself and with the preparation of this 1000 nm thick high quality GaAs film, which is mainly due to the lack of appropriate low cost substrates having small lattice mismatch with GaAs, and also to the expensive deposition facilities strictly restrains the wide acceptance of the related solar electricity in civil utilities. 9 On the other hand, strong light reflection (> 30%) originating from the large refractive index difference between GaAs and the circumstance, e.g., air or vacuum for spacecraft applications demands the development of advanced antireflection coatings (ARCs) not only suppressing light reflection in a wide energy range but also with high stability and/or long-term endurance.…”

Photovoltaic technologies

“…In addition to the possible use of quantum dots as spectral converters, the use of quantum wells and quantum dots has also been proposed to extend the bandgap (Barnham and Duggan, 1990) and as a means to provide multiple electrons from a single photon through impact ionisation (Kolodinski et al, 1993;Ross and Nozik, 1982).…”

“…3G concepts aim to harness some of this wasted energy (Green, 2006). Some of the most interesting 3G concepts discussed over the last 30 years include multi-junction systems such as tandem cells (Henry, 1980), the use of quantum wells and quantum dots to enhance absorption (Barnham and Duggan, 1990), the use of fluorescent collectors (Goetzberger and Greubel, 1977;Weber and Lambe, 1976), impact ionisation to utilise the kinetic energy of carriers (Kolodinski et al, 1993;Landsberg et al, 1993), the use of impurity levels (Corkish and Green, 1993) and hot-electron effects (Ross and Nozik, 1982). While many of these exciting ideas have fired the imagination and provided interesting debate, most have proven very difficult to demonstrate in principle and have often only ever served to manage to decrease the overall efficiencies of devices they hoped to improve.…”