Thinned GaInP/GaInAs/Ge solar cells grown with reduced cracking on Ge|Si virtual substrates

Abstract

Reducing the formation of cracks during growth of GaInP/GaInAs/Ge 3-junction solar cells on Ge|Si virtual substrates has been attempted by thinning the structure, namely the Ge bottom cell and the GaInAs middle cell. The theoretical analysis performed using realistic device parameters indicates that the GaInAs middle cell can be drastically thinned to 1000 nm while increasing its In content to 8% with an efficiency loss in the 3-junction cell below 3%. The experimental results show that the formation of macroscopic cracks is prevented in thinned GaInAs/Ge 2-junction and GaInP/GaInAs/Ge 3-junction cells. These prototype crack-free multijunction cells demonstrate the concept and were used to rule out any possible component integration issue. The performance metrics are limited by the high threading dislocation density over 2•10 7 cm -2 in the virtual substrates used, but an almost current matched, crack-free, thinned 3-junction solar cell is demonstrated, and the pathway towards solar cells with higher voltages identified.

Advances in the development of high efficiency III-V multijunction solar cells on Ge|Si virtual substrates

“…The theoretical analyses and fits to experimental data are primarily based on the Scattering Matrix Method to analyze the optical processes and on the Hovel model to calculate the photocurrents and recombination currents, as detailed elsewhere [1]- [2][3]. III-V structures are grown by metal-organic chemical vapor deposition (MOCVD) using standard precursors [3].…”

“…Thick Ge layers are deposited by reduced pressure chemical vapor deposition (RP-CVD) [3] and ultrathin Ge films are deposited by radio-frequency, plasma-enhanced chemical vapor deposition (RF-PECVD), using the process parameters explained elsewhere [4]. 0.1 cm 2 solar cells are manufactured using standard photolithography techniques and gold-based metal stacks, except for Si that uses a Pd/Ti/Pd/Al system (details in [1]). III-V MJSC Designs a) GaInP/GaInAs/Ge|Si with Active Ge Bottom Cell.…”

“…Around 8% of indium content seems to be suitable to reduce the layer to 1 μm. Of course, this bandgap reduction -due to indium increase-produces a voltage loss in the 3JSC but, if the material quality is maintained, the effect on the efficiency should be limited as compared to the overall benefits of using Ge|Si templates [1].…”

“…Finally, the thinned design with higher indium content shows a recovered Jsc, although still not reaching the baseline values due to the effect of the bandgap shift in the top cell commented before. The lower bandgaps in the top and middle subcells reduce the Voc, which is also affected by a higher dislocation density in the metamorphic GaInAs subcell [1].…”

Evaluation of electricity generation on GeSn single‐junction solar cell

“…Tandem solar cells of III-V semiconductors can achieve the maximum efficiency, which benefits by an efficient utilization of the solar spectrum and lattice match. Especially, the case of Ge-based III-V triple-junction (TJ) solar cells [1][2][3][4][5] have attracted much attention, which has been widely applied in space for energy supply. To confine the misfit dislocation and minimize the strain, the previous study reported 6 that multijunction (MJ) III-V devices use compositionally graded buffers, which have demonstrated solar-to-electrical conversion efficiency of 39.2% (1 sun AM1.5G).…”