Hot carrier solar cell absorbers: materials, mechanisms and nanostructures

Abstract

The hot carrier cell aims to extract the electrical energy from photo-generated carriers before they thermalize to the band edges. Hence it can potentially achieve a high current and a high voltage and hence very high efficiencies up to 65% under 1 sun and 86% under maximum concentration. To slow the rate of carrier thermalisation is very challenging, but modification of the phonon energies and the use of nanostructures are both promising ways to achieve some of the required slowing of carrier cooling. A number of materials and structures are being investigated with these properties and test structures are being fabricated. Initial measurements indicate slowed carrier cooling in III-Vs with large phonon band gaps and in multiple quantum wells. It is expected that soon proof of concept of hot carrier devices will pave the way for their development to fully functioning high efficiency solar cells.

Hot Carrier and Surface Recombination Dynamics in Layered InSe Crystals

“…The cooling times of hot electrons in InSe single crystals extracted from these data (∼1–3.5 ps) are comparable with the reported values in methylammonium lead-iodide perovskites under similar excitation densities , and significantly slower than those for bulk Si or GaAs . This result is reasonable because the large mass ratio of anion-to-cation in both of these materials (∼1.4:1 for In 2+ :Se 2– and ∼2:1 for Pb 2+ :I – ) results in large phononic band gaps that slow hot carrier cooling …”

“…39 This result is reasonable because the large mass ratio of anion-to-cation in both of these materials (∼1.4:1 for In 2+ :Se 2− and ∼2:1 for Pb 2+ :I − ) 36 results in large phononic band gaps that slow hot carrier cooling. 40 At later times (e.g., 100 ps), the overall TR signal for the B exciton is lower and some of the asymmetry of the features in the TR spectrum returns (Figure 2B and Supporting Information Figure S5), but we suspect that these changes are due to longer-time-scale surface recombination processes, discussed directly below.…”

Bandgap Fluctuations, Hot Carriers, and Band‐to‐Acceptor Recombination in Cu2ZnSn(S,Se)4 Microcrystals

“…The different temperatures of the carriers and the lattice are a natural outcome of the relatively short photocarrier lifetime τ, i.e., . [ 31,32 ] If a minority carrier lifetime is very short, excited carriers with high temperatures will recombine before they can “cool down” to lattice temperature T as a result of carrier–phonon interaction and carrier–carrier scattering. It is known that in kesterite compounds, the actual lifetime of the photoexcited carriers is extremely small and does not exceed values of hundreds of picoseconds.…”

Hot-carrier cooling dynamics of type-II InAs/AlA1-xSbx quantum wells

“…In order to do this, hot carriers must be extracted through energy-selective contacts faster than they emit optical phonons 3 . Since optical phonons subsequently decay into acoustic phonons 4,5 , engineering the photonic, electronic and phononic properties of semiconductors is important for improving HCSC devices [6][7][8][9] .…”