Bifacial photovoltaic performance of semitransparent ultrathin Cu(In,Ga)Se2 solar cells with front and rear transparent conducting oxide contacts

Abstract

We report the bifacial photovoltaic performance of semitransparent ultrathin Cu(In,Ga)Se2 (CIGS) solar cells with Sn-doped In2O3 front and F-doped SnO2 rear contacts prepared using a single-stage co-evaporation process under front- and rear-illumination conditions. The power conversion efficiencies (PCEs) of the solar cells measured at 100 mW/cm2 increased with increasing ultrathin CIGS absorber thickness (200–400 nm), from 6.89 to 9.75% when front illuminated, and from 4.91 to 6.46% when rear illuminated, while the corresponding average visible transmission values (420–720 nm) gradually decreased from 18.53% to 5.06%. The bifacial photovoltaic performance of semitransparent solar cells with 200-nm- and 300-nm-thick CIGS absorber layers was also investigated under low-light conditions (100–10 mW/cm2). The PCE of the solar cell with a 300-nm-thick CIGS absorber layer remained almost constant with decreasing light intensity (100–10 mW/cm2), at ~8% (front illumination) and ~6% (rear illumination), while that of the solar cell with 200-nm-thick layer decreased from 6.84% to 3.43% (front illumination) and from 4.91% to 2.41% (rear illumination). The enhanced bifacial performance of the solar cell with the 300-nm-thick CIGS absorber layer is attributed to high shunt resistance in the solar cell owing to the improved microstructural qualities.