The effects of intraband and interband carrier‐carrier scattering on hot‐carrier solar cells: A theoretical study of spectral hole burning, electron‐hole energy transfer, Auger recombination, and impact ionization generation

Abstract

The effects of carrier‐carrier scattering resulting from the Coulomb‐potential interaction between two electrons on hot‐carrier solar cells are theoretically studied. Theoretical models and explicit formulas for calculating intraband carrier‐carrier scattering rates, electron‐to‐hole energy transfer rates, Auger recombination rates, and impact ionization generation rates are presented and derived. The numerical calculations from these formulas are obtained, and their effects on hot‐carrier solar cells are investigated. Several findings can be concluded from this study: (1) Intraband electron‐electron scattering and hole‐hole scattering are normally fast enough to randomize carrier distribution in the momentum space and thus maintain quasiequilibrium to establish electron and hole temperatures at a steady state; (2) spectral hole burning in hot‐carrier solar cells can be incurred by fast carrier extraction processes through energy‐selective contacts and slow intraband carrier‐carrier scattering; (3) energy transfer between electrons and holes via intraband electron‐hole scattering cannot guarantee that electrons and holes will maintain the same carrier temperature for hot‐carrier solar cells in all cases, especially if the difference between electron and hole temperatures is smaller than 100 K; and (4) materials with a band‐gap energy larger than 1 eV are favorable as conventional solar cells in which Auger recombination is not significant. On the contrary, materials with a band‐gap energy smaller than 0.5 eV are not suitable for conventional solar cells due to the detrimental effects of Auger recombination. However, they are ideal materials for realizing hot‐carrier solar cells due to beneficial effects of impact ionization generation, although these beneficial effects can be undermined by spectral hole burning.

There is plenty of room at the top: generation of hot charge carriers and their applications in perovskite and other semiconductor-based optoelectronic devices

“…This stage is attained very rapidly (<100 fs) and is referred to as “thermal equilibration” or “carrier thermalization” 22 . The temperature of these species generally reaches from 2500 to 4500 K under 1 and 100 sun illumination, respectively 22 , 25 . The second stage of HC relaxation starts with their equilibration with the lattice through carrier–phonon inelastic interaction until the temperature of both lattice and HC becomes equal.…”

“…An interested reader may refer to refs. 25 , 29 for further detailed insights. Although, the hot species attain an equilibrium among themselves, they are far from equilibrium when compared to the lattice, and no phonon generation has yet taken place at this stage.…”

“…However, in a conventional solar cell, the equation reduces to as the HC relax to T L . In conventional PV devices, there is much emphasis on particle extraction rather than energy extraction 25 .…”

Hot‐carrier solar cells and improved types using wide‐bandgap energy‐selective contacts

“…5,20,23 The required τ eq value for preventing the carrier depletion and achieving high η PV is shorter at shorter τ th and τ re and also affected by the characteristics of the ESCs. 23 The effect of the ESCs is discussed at the end of Section 3.2.…”

“…3,4 These models have been improved for evaluating the impacts of finite values of these parameters, showing that the requisites for high conversion efficiency are a carrier thermalization time longer than 1 ns and an energy-selection width of the QD-ESC narrower than 0.1 eV. 5,6,[19][20][21][22][23][24] Then, two improved types of HC-SCs that utilize sub-bandgap photons have been proposed for further higher efficiency: an HC-SC with intraband transition (HC-SC+intra) and an intermediate-band-assisted HC-SC (IB-HC-SC), and their performance was analyzed using similar models. [25][26][27][28] In the present study, I construct a new model based on the previous ones to evaluate the impacts of three realistic points of great importance.…”