A. Le Bris

Hot carrier solar cells: Achievable efficiency accounting for heat losses in the absorber and through contacts

The hot carrier solar cell enables the photovoltaic efficiency limit to be approached by tapping into what are normally heat losses. Previous models neglected thermalization in the absorber and assumed ideally energy selective contacts that allow minimum heat losses upon carrier extraction. The proposed improved model includes both realistic contacts and thermalization rates. The heat flux due to carrier extraction is computed. Results show that spectrally broad semiselective contacts are compatible with an efficiency exceeding the single junction limit, which would considerably facilitate the realization of the device.

Thermalisation rate study of GaSb-based heterostructures by continuous wave photoluminescence and their potential as hot carrier solar cell absorbers

GaSb-based heterostructures are tested as candidates for a hot carrier solar cell absorber. Their thermalisation properties are investigated using continuous wave photoluminescence. Non-equilibrium carrier populations are detected at high excitation levels. An empirical expression of the power lost by thermalisation is deduced from the incident power dependent carrier temperature. The experimentally determined thermalisation rate is then used to simulate the potential efficiency of a hot carrier solar cell, showing a significant efficiency improvement compared to a fully thermalised single p–n junction of similar bandgap.

Self-organized ordered silver nanoparticle arrays obtained by solid state dewetting

Spontaneous dewetting of a silver layer on a templated silica substrate is proposed as a promising low-cost process to produce self-organized metallic nanostructures. Periodic gratings with inverted pyramid pattern and periods ranging from 200 to 1000 nm are fabricated by nanoimprint on a sol-gel silica layer. A silver layer is then deposited on the templated substrate by magnetron sputtering and annealed to form an array of well-organized islands by solid-state dewetting. The resulting islands are shown to have reduced diameter and size dispersion compared to arrays obtained in the same conditions on flat substrates. The density of defects in the periodic array is determined as a function of silver layer thickness and is lower than 10% in optimal conditions. Optical transmission spectra of periodic arrays are measured, showing extinction peaks that can be related to plasmon resonance. This resonance can be tuned by adjusting the period and particle diameter.

Hot carrier solar cells: Challenges and recent progress

The limiting efficiency on the conversion efficiency of terrestrial global sunlight is not circa 31%, as commonly assumed, but 74%. To reach the lowest possible costs and hence to attain its intrinsic potential as a major source of future sustainable energy supplies, it would appear photovoltaics has to evolve to devices targeting the latter efficiency rather than the former. The hot carrier solar cell, although presenting substantial device challenges, is arguably the highest efficiency photovoltaic device concept yet suggested and hence worthy of efforts to investigate its practicality. Challenges in the implementation of hot carrier cells are identified and progress in overcoming these are discussed.

Hot carrier solar cells: The device that did not exist (but should)

Hot carriers are an unusual type of solar cell, very efficient in principle but where electronic, optical and thermal effects are inextricably mixed. Modeling was used first to understand the device operation. Then more detailed simulations were made on phononic properties of the nanostructures absorbing material using DFT-based molecular dynamics and electron-electron and electron-phonon interactions using a Monte Carlo approach.

Hot carrier solar cell efficiency simulation with carrier extraction through non ideal selective contacts

The hot carrier solar cell is an innovative concept of high efficiency 3rd generation photovoltaic, where thermal losses are reduced by slowing the electron thermalization. Such cells offer maximal potential performance equivalent to an ideal multi-junction cell. Energy selective contacts are necessary to insulate the “hot” carriers in the absorber from the “cold” carriers in the outside world. These contacts allow only electrons with one specific energy to be collected. Here we propose a model of a cell with realistic contacts allowing transmission of electrons within a narrow energy range. The influence of the transmission range of the contact on the cell efficiency and on thermal losses is investigated. We show that, in some specific conditions, the acceptable energy width of the selective contacts can be large and semi-selective contacts allow significant efficiency enhancement.