Performance evaluation of heterogeneously integrated 3J InGaP/GaAs/Si tandem solar cells on Si substrate for concentrated photovoltaics

Integration of III-V multijunction solar cells on Si substrate is highly sought for achieving lower levelized cost of energy by unifying the high-efficiency merits of III-V materials with low-cost and abundance of Si. Triple-junction (3J) InGaP/GaAs/Si solar cells with an active Si bottom cell are investigated for concentrated photovoltaic (CPV) operation under AM1.5d spectrum. We present key insight into the design of GaAs buffer architecture for the optimal down-selection of the buffer doping and thickness to maximize the photon flux penetration to the bottom Si subcell. Ideal case scenario employing dislocations free III-V solar cells directly integrated onto the Si subcell without a buffer layer yielded current-matched 1-sun 3J efficiency of 32.13% and 36.39% under AM1.5d and AM1.5g spectra, respectively. Under AM1.5d the efficiency dropped to 29.30% and 27.32% at a threading dislocation density (TDD) of 10⁶ cm^-2 and 10⁷ cm^-2, respectively, when 0.5 μm thick GaAs buffer was employed between the III-V subcells and the bottom Si subcell. Finally, we present a novel design for heterogeneously integrated 3J InGaP/GaAs/Si tandem solar cell incorporating a TDD of 10⁶ cm^-2 with an efficiency exceeding 33% at 200 suns, indicating a promising future for III-V on Si photovoltaics for CPV operation.