Mixed co-solvent engineering of PEDOT:PSS to enhance its conductivity and hybrid solar cell properties
Conducting polymers, such as poly(3,4-ethylenedioxy thiophene):poly(styrenesulfonate) (PEDOT:PSS), have gained significant interest for their use in organic and organic–inorganic electronic device applications. Further enhancement in the conductivity of this polymer could accelerate its widespread use in electronic device applications. In addition, hybrid solar cells made of this p-type conducting polymer on Si have attracted a lot of attention in the fabrication of low-cost high-efficiency devices. Here, we demonstrate the effect of adding a mixed co-solvent of ethylene glycol and methanol in PEDOT:PSS to improve its conductivity and hence to enhance the performance of a hybrid planar Si solar cell. Based on our results, we establish a morphological model to explain the microstructure modification of PEDOT and PSS that contributes to the enhanced properties. We are able to engineer a thinnest PSS layer around individual PEDOT grains by adding a mixed co-solvent in PEDOT:PSS and achieve a highly conducting PEDOT:PSS film and a PEDOT:PSS/planar-Si cell with the highest photoconversion efficiency of 14.6% reported to date. Our present approach to generate highly conductive PEDOT:PSS by mixed co-solvent addition can also be used to improve the performance of other organic electronic devices based on PEDOT:PSS.