Energy Selective Contacts Research Articles

Progress on hot carrier cells

Hot Carrier cells aim to collect hot carriers resulting from photon absorption before they thermalise. This requires slowed carrier cooling in an absorber material and collection through narrow energy selective contacts. Previous work has proved the concept of these energy selective contacts using resonant tunnelling in Si quantum dot (QD) double-barrier structures. Further experimental work on electrical and optical excitations of these structures is shown. Modelling work has demonstrated the possibility of slowing the rate of carrier cooling by modifying the phonon dispersion in QD superlattices. Developments in this modelling which indicate the critical importance of the interface are also presented.

Selective energy contacts for hot carrier solar cells

The concept of the hot carrier cell is to absorb a wide range of photon energies and to separate the resulting “hot” carriers before thermalisation within a narrow range of energies onto external electrodes. Proof of concept of selective energy contacts has been demonstrated for double barrier resonant structures using Si quantum dots for resonant energy levels using current–voltage measurement with and without optical excitation and conductive atomic force microscopy. Si quantum dot resonant tunnelling structures are fabricated by thin film deposition followed by Si solid state precipitation in a SiO 2 matrix, with the size uniformly controlled by the layer thickness. Further characterisation and approaches to optimization are discussed.

Electronic and thermal transport in hot carrier solar cells with low-dimensional contacts

Hot carrier solar cells are a third generation solar cell device where electrons and holes, heated by solar radiation, are removed from the absorber via low-dimensional energy selective contacts before they can thermalise to the band edge. Here, a new model is presented for calculating the performance of these devices, which takes into account the energy spectrum of the contacts. It is shown that efficiency is maximised with a certain ideal number of contacts and that the energy spectra of these should be narrow.

Resonant tunneling through defects in an insulator: Modeling and solar cell applications

In this paper, a model for electron tunneling through defects in an insulator is presented. The three-dimensional results for the electron transmission coefficient can be obtained by characterizing the tunneling process in terms of a defect density and capture cross section. Fitting the model parameters by comparison with the results of a full three-dimensional tunneling-through-defect simulation, this model can be used to calculate and predict the electron transmission for various spatial distributions of defects without performing the complex three-dimensional calculations. Energy selective contacts using the resonant tunneling for carrier extraction have been proposed as a means to achieve a higher efficiency in future generations of photovoltaic devices. Resonant tunneling through defects in an insulator, where the defects may be atoms or quantum dots, may provide a possible implementation for such energy selective contacts. With the present model, the influences of the tunneling effective mass, insulator thickness, and defect distribution on the electron transmission coefficient have been investigated. The results suggest that the introduced defects should lie in the middle of a reasonably thick insulator to improve the carrier energy selectivity.