Effects of Al2O3 Rear Interface Passivation on the Performance of Bifacial Kesterite‐Based Solar Cells with Fluorine‐Doped Tin Dioxide Back Contact

Herein, ultrathin Al 2 O 3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO 2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al 2 O 3 ‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al 2 O 3 layer reduces the short‐circuit current density ( J SC ), resulting in poor device efficiency. On the other hand, significantly higher J SC is realized for mixed sulfide and selenide kesterite devices with Al 2 O 3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al 2 O 3 to 4.6% for those with Al 2 O 3 . Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al 2 O 3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study.