Modeling lattice-matched InP-based multijunction solar cells

Abstract

Currently, the multijunction solar cell structure gives the highest efficiency for photovoltaic solar cells. In this study, tandem, triple, and quadruple junction multijunction solar cell structures that include an InP subcell on InP substrate were investigated. A model that can calculate both the voltage-current characteristics and external quantum efficiency was demonstrated. The model gave fitted results with the experimental data for a single junction GaAs solar cell and a tandem solar cell that provides efficiency higher than 30%. The model was used to optimize the lattice-matched AlAsSb/InP tandem, AlAsSb/InP/InGaAsP triple, and AlAsSb/InP/InGaAsP/GaAsSb quadruple junction solar cell designs and the highest efficiencies obtained for these cells were 29.9%, 36.69%, and 42.79%, respectively, under AM1.5 spectrum without any sun concentration. This lattice-matched quadruple junction structure gives the opportunity of having high efficiency without wafer bonding.

Modeling Lattice Matched Dilute Nitride Triple and Quadruple Junction Solar Cells on Virtual SiGe Substrate

“…All three subcells include n-type emitter and p-type base layers. Similar to the literature [27,32], the doping concentration and thickness of emitter layers for three junctions are assumed to be 10 18 cm −3 and 100 nm, respectively. The doping concentrations of the base layers are 10 17 cm −3 and the thicknesses are tuned for highest efficiency.…”

“…Semiconductor transport equations, drift-diffusion current equations and the Poisson equation are used together to model semiconductor devices such as single junction and multijunction solar cells [32,33]. When modeling a conventional p-n junction solar cell, the electric field and the drift current is assumed to be zero outside the space charge region of the junction.…”

“…Therefore, the minority electrons create the diffusion current in the p side and minority holes carry the diffusion current in the n side and the drift current is dominant in the space charge region. When a diffusion current equation is inserted into transport equations, the following equations are obtained for p and n sides [32,33]. Equations derived from continuity and drift-diffusion current equations are solved to analyze the p-n junctions [33].…”

“…The generation rates of the subcells other than the top cell are affected by the upper subcells because the higher energy photons of the spectrum are absorbed by them. Therefore, the generation rate of nth subcell can be expressed as [32]:…”