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

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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.