Abstract
Current–voltage (I–V) curves and operational stability of hot-carrier solar cells are studied by a non-equilibrium theory considering three characteristic timescales of the hot-carrier dynamics (timescales for the extraction, equilibration, and thermalization). We find a hysteresis behavior in the I–V curves of high-efficiency hot-carrier solar cells, which could result in an operational instability. For practical application, we point out two types of instabilities that can degrade the device efficiency: one is intrinsic in a single cell and the other arises when plural cells are series-connected. It is also found that particle-number non-conserving processes, Auger recombination and impact ionization, increase the stability, showing an advantage of using a semiconductor material with a large Auger recombination coefficient for the light absorber.
Highlights
The hot-carrier solar cell (HCSC)[1] is one of the thirdgeneration photovoltaic cells to achieve a high power conversion efficiency largely exceeding the detailed-balance limit, known as the Schockley–Queisser (SQ) limit.[2]
It is claimed that including particle-number non-conserving processes, e.g., impact ionization (II) and Auger recombination (AR), which naturally come into play at high carrier temperatures, is necessary to predict reliable I–V curves for HCSCs, which, is not an easy task in simulation
III A, a numerical simulation is performed with a particle-number conserving (PC) model where the number nonconserving processes (e.g., AR and II) are neglected
Summary
The hot-carrier solar cell (HCSC)[1] is one of the thirdgeneration photovoltaic cells to achieve a high power conversion efficiency largely exceeding the detailed-balance limit, known as the Schockley–Queisser (SQ) limit.[2]. The past theoretical papers mainly focus the conversion efficiencies at the max power conditions, while the current–voltage (I–V) characteristics have been rarely discussed.[5–8] The main reason might be related to an issue raised by Würfel et al.,[9] where it is claimed that the particle-number conserving (PC) model[1] predicts less reliable I–V curves with unrealistically high hot-carrier temperatures. We show that a hysteresis behavior is found in the I–V curves and causes instability on the steady-state operation in one-cell device and/or in a module of series-connected plural HCSCs. it is found that II and AR effects can stabilize the steady states of HCSCs and a stable operation with a high conversion efficiency above 50% could be obtained with an absorber of Eg 1⁄4 0:93 eV under an illumination of 1000 suns, if the absorber has a large AR coefficient, CAR ! It is found that II and AR effects can stabilize the steady states of HCSCs and a stable operation with a high conversion efficiency above 50% could be obtained with an absorber of Eg 1⁄4 0:93 eV under an illumination of 1000 suns, if the absorber has a large AR coefficient, CAR ! 10À28 cm6/s
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