On the influence of the photo-induced leakage current in monolithically interconnected modules

This paper describes the influence of an irradiance-dependent photo-induced leakage current through a semi-insulating GaAs substrate on the performance of photovoltaic monolithically series-interconnected multisegment laser power converters. A reciprocal relation between the resistivity of a semi-insulating GaAs substrate and irradiance of monochromatic light is experimentally observed. A reduced resistivity of the substrate with an increasing irradiation results in a substantial increase of a leakage current through the semi-insulating GaAs substrate between adjacent segments. For a multisegment laser power converter, this photo-induced leakage current is identified as a major shunting mechanism between adjacent segments that arises under high irradiances. Open-circuit voltage Voc, fill factor (FF), and consequently conversion efficiency of a multisegment laser power converters are highly affected by the shunting mechanism. Based on a shading experiment, we observed that Voc drops up to 21.5 mV per segment at a short-circuit current density Jsc=47.3A/cm2 for the studied six-segment MIM specimen. For the same device, FF drops by 4.1% absolute at Jsc=40.5A/cm2. For the two-segment specimen, 5.8 mV drop of Voc per segment and 1.5% absolute drop in FF is reported at Jsc=47.3 and 43.7A/cm2, respectively.