Modelling of GaAsP/InGaAs/GaAs strain-balanced multiple-quantum well solar cells

Abstract

A design of de GaAsP/InGaAs/GaAs solar cell is presented that allows to model high efficiency devices. The stress, tensile and compressive, are considered in order to compute the electron and hole dispersion relation E(k) in conduction and valence band. Similarly, the optical transitions in quantum well and barriers were evaluated to calculate the quantum internal efficiency and the photocurrent. GaAsP/InGaAs/GaAs solar cell is optimized to reach the maximum performance by means of J-V relation. Our model was used to determine the highest efficiencies for cells containing quantum wells under varying degrees of strain, showing that cells with strained quantum wells achieve high efficiencies.

Anisotropic emission and photon-recycling in strain-balanced quantum well solar cells

“…In a previous paper, 3 it was shown that high SB-QWSC performance was achieved for 3% In composition. Moreover, for SB-QWSC with deeper quantum wells (higher indium fraction) the efficiency falls.…”

“…Once the expressions for the effective density of states, the absorption coefficient, the radiative recombination current density, and photocurrent were found for SB-QWSC, then it is possibly to compute the J-V characteristic, and conversion efficiency (g) can be evaluated. 3,16 The dependence of conversion efficiency on back mirror reflectivity and quantum well number (N w ) is examined in Figure 6. This plot suggests that with the addition of a distributed Bragg reflector in the device, fewer quantum wells are required to grow in the i-region in order to achieve high performance.…”

“…17 This behavior is shown in Figure 7, where we have examined the conversion efficiency as a function of solar concentration for optimized GaAs 0.96 P 0.04 /In 0.03 Ga 0.97 As/GaAs solar cell with 20 nm quantum well width. 3 We used r A ¼ 0.1, r B ¼ 0.95, and resistive effects were neglected. It can be observed how the conversion efficiency should increase with solar concentration up to 1000 suns.…”

“…In order to determine the QW energy levels in the hh and lh bands under varying compressive strain a 4 Â 4 kÁp Kohn-Luttinger Hamiltonian was used. 3 Furthermore, valence band structure for holes in the quantum well was calculated using a 4 Â 4 kÁp Hamiltonian model. The DE f values for the AM1.5 solar spectrum 10 were computed for a more general method to the one reported by Tsiu et al 11 We assumed that the number of photogenerated carrier pairs is equal to the total emitted photo flux.…”

“…This behavior was demonstrated in previous work. 3 As a consequence of this behaviour, compressive strain results in lower thermal occupancy of the lh band relative to the hh band, and radiative transitions from the conduction to the hh band are favored over those to the lh band. If the splitting becomes greater than a few $k B T, lh transitions may be almost entirely suppressed.…”