Efficient hole collection by introducing ultra-thin UV–ozone treated Au in polymer solar cells

Efficient hole collection in polymer solar cells (PSCs) has been achieved by introducing an ultra-thin UV–ozone (UVO) treated Au on indium tin oxide (ITO) to substitute poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Through optimizing the Au thickness and the duration of UVO treatment, it is shown that the ITO/Au (1 nm) treated by UVO for 15 s improves the fill factor significantly to 67.2% and power conversion efficiency (PCE) to 3.47%, which is competitive to that of the PEDOT:PSS-based PSCs with PCE of 3.38%. The results of ultraviolet photoemission spectroscopy and the analysis of the current conduction mechanism show that the UVO-treated Au offers favorable band alignment at metal/polymer interface of the anode for efficient hole collection. Meanwhile, the series resistance of the device decreases drastically.