MoS2 Nanosheets Exfoliated by Sonication and Their Application in Organic Photovoltaic Cells

초록

The use of sonication to control the properties of MoS2 nanosheets fabricated using MoS2 powder and N-vinyl-2-pyrrolidone as starting materials was investigated. Application of 200 W of power for 8 h to MoS2 powder yielded exfoliated MoS2 nanosheets containing 0.65-nm-thick single layers and several-nanometer-thick few-layers with a lateral size of 100-300 nm. The absorption peaks were found and photoluminescence emission peaks appeared at 520, 620, and 680 nm after exfoliation, which were not seen in the bulk MoS2, indicating a change from indirect band gap to direct band gap. The reduction in the peak difference between E-2g(1) and A(1g) in the Raman spectra confirmed the exfoliation of MoS2 by the sonication process. The work-function of MoS2 is measured to be 4.6 eV and it increased to 4.9 eV after UV/ozone treatment for 15 min. The power conversion efficiency (PCE) of an organic photovoltaic cell with a UV/ozone-treated MoS2 layer as the hole extraction layer (HEL) was 2.12%, which was higher than that without HEL, 1.84%. The increase in the PCE is considered to result from the band alignment due to the presence of a UV/ozone-treated MoS2 layer.

키워드