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.