Efficiency of hot-carrier solar energy converters

Abstract

A single-threshold quantum-utilizing device in which the excited carriers thermally equilibrate among themselves, but not with the environment, can convert solar energy with an efficiency approaching that of an infinite-threshold device. Such a hot-carrier flat-plate device operated under typical terrestrial conditions (AM 1.5 illumination, 300 K) can convert solar energy with an efficiency of 66%, substantially exceeding the 33% maximum efficiency of a quantum device operating at thermal equilibrium, and the 52% maximum efficiency of an ideal thermal conversion device. This high efficiency is achieved in part through an unusual inversion, in which the chemical potential of the excited electronic band is below that of the ground band. This negative potential difference reduces radiation losses, permitting a low threshold energy, and a high Carnot efficiency resulting from a high carrier temperature.

Hot carrier solar cell as thermoelectric device

“…The idea of hot carrier solar cell was proposed by Ross and Nozik in attempt to overcome Shockley-Queisser efficiency limit of 31% at 1 Sun (or 41% at full concentration) in a simple photovoltaic device [1]. Conceptual implementations of Würfel and other researchers are known [2,3] and are presented in the following in some detail.…”

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.…”

Effect of external applied electric field on the silicon solar cell’s thermodynamic efficiency

“…After them, many studies have been carried out to explore the possibilities of exceeding this limit. Different technologies and methods were used for that purpose [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Among these approaches, we could cite tandem cells, concentrator cell, carrier multiplication, down conversion, hot carriers, etc.…”