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 V
_oc
, 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 V
_oc
drops up to 21.5 mV per segment at a short-circuit current density J
_sc
= 47.3 cm
²
for the studied six-segment MIM specimen. For the same device, FF drops by 4.1% absolute at J
_sc
= 40.5 A/cm
²
. For the two-segment specimen, 5.8 mV drop of V
_oc
per segment and 1.5% absolute drop in FF is reported at J
_sc
= 47.3 and 43.7 A/ cm
²
, respectively.