Dual use of tantalum disulfides as hole and electron extraction layers in organic photovoltaic cells

UV/ozone treated (UVO-treated) TaS₂ and non-treated TaS₂ nanosheets are introduced into organic photovoltaic cells (OPVs) as hole extraction layers (HEL) and electron extraction layers (EEL). TaS₂ nanosheets are obtained via ultrasonic vibration and size-controlled by centrifugation. Atomic force microscopy (AFM) images reveal that the thickness and lateral size of TaS₂ nanosheets are approximately 1 and 70 nm, indicating that uniform and ultrathin TaS₂ nanosheets are obtained. The work function of TaS₂ increases from 4.4 eV to 4.9-5.1 eV after applying UVO treatment by forming Ta₂O₅. In addition, the power conversion efficiencies of normal OPV with UVO-treated TaS₂ and inverted OPV with TaS₂ are 3.06 and 2.73%, which are higher than those of OPV without TaS₂ (1.56% for normal OPV and 0.22% for inverted OPV). These results indicate that TaS₂ is a promising material for HEL and EEL layers in OPVs.