Enhancement of hot carrier effect and signatures of confinement in terms of thermalization power in quantum well solar cell

Abstract

A theoretical model using electron-phonon scattering rate equations is developed for assessing carrier thermalization under steady-state conditions in two-dimensional systems. The model is applied to investigate the hot carrier effect in III-V hot-carrier solar cells with a quantum well absorber. The question underlying the proposed investigation is: what is the power required to maintain two populations of electron and hole carriers in a quasi-equilibrium state at fixed temperatures and quasi-Fermi level splitting? The obtained answer is that the thermalization power density is reduced in two-dimensional systems compared to their bulk counterpart, which demonstrates a confinement-induced enhancement of the hot carrier effect in quantum wells. This power overall increases with the well thickness, and it is moreover shown that the intra-subband contribution dominates at small thicknesses while the inter-subband contribution increases with thickness and dominates in the bulk limit. Finally, the effects of the thermodynamic state of phonons and screening are clarified. In particular, the two-dimensional thermalization power density exhibits a non-monotonic dependence on the thickness of the quantum well layer, when both out-of-equilibrium longitudinal optical phonons and screening effects are taken into account. Our theoretical and numerical results provide tracks to interpret intriguing experimental observations in quantum well physics. They will also offer guidelines to increase the yield of photovoltaic effect based on the hot carrier effect using quantum well heterostructures, a result critical to the research toward high-efficiency solar cell devices.

Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells

“…Hereby, the thermalization power density of hot carriers is determined based on their scattering with LO phonons through Froḧlich interactions and their relaxation via inter-and intra-sub-band transitions in idealized, phase-pure ZB InGaAs NWs. 46 In this approach, the range of diameters is chosen to be smaller than the actual values of the studied NWs due to computational time. However, all of the diameters are chosen to be larger than the Bohr radius of InGaAs, to simulate the bulk properties of the NWs while taking into account the confinement effect by employing a quantized wave function in the transverse (crosssectional) plane perpendicular to the axis of the NWs.…”

“…To investigate the origin of this rather intriguing behavior, further theoretical and experimental analyses are carried out to reveal the impact of different electron–phonon scattering rates and carrier dynamics under steady-state conditions in 1D InGaAs/InAlAs core–shell NWs. Hereby, the thermalization power density of hot carriers is determined based on their scattering with LO phonons through Fröhlich interactions and their relaxation via inter- and intra-sub-band transitions in idealized, phase-pure ZB InGaAs NWs . In this approach, the range of diameters is chosen to be smaller than the actual values of the studied NWs due to computational time.…”

Long-Lived Coherent Acoustic Phonons in Epitaxially Grown III-V Adiabatic Cavities

“…Interestingly, the phonon mini gap in the ADBR sample (5 GHz= 0.02 meV) is also much smaller than 18 meV (half of the optical phonon energy 36 meV in GaAs at Γ-point) required to inhibit Klemens decay [41]. A retarded excess energy loss rate in phononic cavities compared to the SL sample could be a manifestation of hot phonon reabsorption arising from impeded LA-LA phonon scattering [42,43]. However, the intricacy of scattering mechanisms in superlattices, see in [44] and cited literature therein, driving photoexcited carriers energy loss require further investigations.…”

Hot-carrier thermophotovoltaic systems

“…This can be achieved by extracting the hot carriers using energy-selective contacts [29,30], and results in a theoretical efficiency limit of 85% for zero bandgap under full concentration [22]. Although the experimental efficiency of HCSC remains currently limited due to strong thermalization rates in most materials, promising avenues have been identified [31,32], using ultrathin [33] and low-dimensional absorbers, such as quantum wells [34][35][36][37], nanowires [38] and dots [39], or hybrid hot-carrier multi-junction devices [40,41].…”