Impact of Strain Accumulation on InGaAs/GaAsP Multiple-Quantum-Well Solar Cells: Direct Correlation between In situ Strain Measurement and Cell Performances

摘要

The effects of accumulating strain inside InGaAs/GaAsP multiple-quantum-well (MQW) solar cells were investigated and their correlation with in situ wafer curvature measurement was examined. The p-i-n GaAs solar cells, containing 20-period InGaAs/GaAsP MQWs in an i-GaAs layer, were fabricated by metalorganic vapor phase epitaxy. The strain inside MQWs was varied by changing In content in an InGaAs well, while maintaining other parameters. As evidenced by curvature transience, the excessive strain led to lattice relaxation, resulting in defects, dislocations, and poor crystal quality. Consequently, short circuit current density and open circuit voltage deteriorated, and solar cell performance degraded. The highest conversion efficiency was obtained in a strain-balanced MQW solar cell. InGaAs/GaAsP MQWs have a great potential for extending the absorption edge of GaAs cells and for enhancing the efficiency of Ⅲ/ Ⅴ multijunction solar cells by current matching. Hence, the growth of InGaAs/GaAsP MQWs for photovoltaic application requires a strain monitoring system and careful control such that the accumulating strain is minimized.