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The optical absorption is the most important macroscopic process to characterize the microscopic optical transition in the semiconductor materials. Recently, great enhancement has been observed in the absorption of the active region within a p–n junction. In this paper, GaAs based p–i–n samples with the active region varied from 100 nm to 3 μm were fabricated and it was observed that the external quantum efficiencies are higher than the typical results, indicating a new mechanism beyond the established theories. We proposed a theoretical model about the abnormal optical absorption process in the active region within a strong electric field, which might provide new theories for the design of the solar cells, photodetectors, and other photoelectric devices. [ABSTRACT FROM AUTHOR]

Highlights • The TFSC is on a metallic thin film instead of the GaAs parent substrate. • Electroplating is employed to prepare the metal carrier instead of bonding generally used. • The substrate transferred process based on electroplating imposes little strain on the epilayers. • The TFSCs show a high efficiency, light weight, super thin style, flexibility and performance uniformity. • The flexibility is investigated by bending the TFSCs into different strain and with various bending recycles. Abstract 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 μm, 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. [ABSTRACT FROM AUTHOR]