Stress Analysis of Flexible GaInP/GaAs/InGaAs Solar Cells Based on Cu Thin-Film Substrates

The stress of GaInP/GaAs/InGaAs triple-junction (3J) solar cells with different thicknesses of Cu thin-film substrates is analyzed. X-ray diffractometer and metallographic examination show that the unstable as-deposited Cu film undergoes room-temperature self-annealing, which results in grain growth and changes the internal stress of the Cu film over time. A suitable Cu thickness (18 mu m) for 3J solar cells is obtained, whose internal stress can offset the stress caused by the epitaxial mismatch. The flexible 3J solar cell with 18 mu m Cu film has the lowest curvature of 8.24 m(-1) under the combined effect of thermal stress and lattice mismatch stress. The photovoltaic conversion efficiency reaches 35.02% with the open-circuit voltage of 3.03 V under AM1.5G spectrum. Cu films with a thickness of 14-28 mu m have little effect on the optoelectronic properties of the final device. Reducing the curvature of lattice-mismatched GaInP/GaAs/InGaAs solar cell devices is beneficial for realizing large-scale flexible solar cell modules.