Flexible four-junction inverted metamorphic AlGaInP/AlGaAs/ In0.17Ga0.83As/In0.47Ga0.53As solar cell

Abstract A flexible four-junction (4 J) AlGaInP/AlGaAs/In0.17Ga0.83As/In0.47Ga0.53As solar cell with the band gap energy of 1.92/1.53/1.18/0.82eV was fabricated. Taking advantages of aluminum (Al)-contained material as well as metamorphic growth, the design of multiple junction solar cells became much easier and more flexible. In order to accommodate lattice mismatch between two InGaAs sub cells, compositionally step-graded AlGaInAs buffer layers were applied to release the mismatch strain during the inverted metamorphic (IMM) 4 J solar cells growth. A flexible 4 J solar cell on a 50 μm thick polyimide (PI) film was successfully fabricated by using temporary bonding and epitaxial layer lift-off via selective wet chemical etching. A conversion efficiency of 25.76% (AM1.5G) with an open circuit voltage of 3.46V, a short-circuit current density of 9.07 mA/cm2 and a fill factor of 82.14% was obtained without anti-reflection coating (ARC), and it would be higher than 32% by ARC integration. The mass density of the 4 J flexible solar cell was only 467  g/m2, and the specific power was up to 550 W/kg.