Characteristics of InGaP/GaAs double junction thin film solar cells on a flexible metallic substrate

We have investigated the characteristics of InGaP/GaAs double junction thin film solar cells (TFSCs) on a flexible metallic substrate prepared by electroplating copper (Cu). Both photoluminescence peaks of InGaP and GaAs sub-cells maintained the original positions after transferring the epilayers onto Cu carrier, but a peak shift occurred when the epilayers were bent under intense strain. A slight efficiency improvement up to 29.09% was obtained, compared with 28.25% of conventional structure with GaAs grown substrate under air mass 1.5 (AM1.5) illumination. The TFSCs have a total thickness of about 30 mu m, showing an excellent flexibility. Performance measurements of TFSCs were conducted under different strain by bent into the corresponding central angles. It was found that the efficiency was keeping more than 90% when the strain was less than 0.1%, although a rapid decrease down to below 45% occurred till the strain was increased to 0.2%. The favorable performance maintaining after up to 100 bending recycles proved the superior mechanical stability of the TFSCs. Our presented transferring substrate technology based on electroplating in this paper enables the TFSCs with an outstanding performance uniformity, a high yield and a large power weight ratio, which will exhibit an enormous potential to fabricate flexible, low-weight, thin film optoelectronic devices.