UV/ozone-treated WS2 hole-extraction layer in organic photovoltaic cells

초록

WS2 nanosheets obtained through a simple sonication exfoliation method are employed as a hole-extraction layer to improve the efficiency of organic photovoltaic cells (OPVs). A reduction in the wavenumber difference in the Raman spectra, the appearance of a UV absorption peak, and atomic force microscopy images indicate that WS2 nanosheets are formed through the sonication method. The power conversion efficiency (PCE) values of OPVs with and without untreated WS2 layers are both 1.84%. After performing a UV-ozone (UVO) treatment on the WS2 surface for 15 min, the PCE increases to 2.4%. Synchrotron radiation photoelectron spectroscopy data show that the work function of WS2 increases from 4.9 eV to 5.1 eV upon UVO treat- ment, suggesting that the increase in the PCE value is caused by the band alignment. Upon inserting poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT: PSS) between the WS2 and the active layer, the PCE value of the OPV increases to 3.07%, which is superior to that of the device employing only PEDOT:PSS (2.87%). Therefore, it is considered that the use of UVO-treated WS2 is able to improve the performance of OPV cells. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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