PPy:PSS as alternative to PEDOT:PSS in organic photovoltaics

Polypyrrole-polystyrene sulfonate (PPy:PSS) thin films have been electrodeposited on indium tin oxide (ITO)-coated glass slides and used as hole transport layers (HTLs) in poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT:PCBM)-based organic photovoltaics (OPVs). The OPVs made with PPy:PSS exhibit performance (PCE = 2.50%, JSC = 9.03 mA/cm2, VOC = 0.57 V, FF = 0.49) comparable to that obtained by using standard poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) spin-coated films (PCE = 2.62%, JSC = 9.43 mA/cm2, VOC = 0.54 V, FF = 0.52). Using XPS, it is shown that electrodeposited PPy:PSS does not etch the ITO electrode, in contrast to the known degradation effect of the PSSH acid excess present in spin-coated PEDOT:PSS. The effects of the film thickness and the rate of electropolymerization of PPy:PSS have been investigated to show that the only main adverse affect on the OPVs performance is the decreased transparency of the films at higher thicknesses. The results reported here indicate that stable electrodeposited PPy:PSS can be successfully used in place of ITO-etchant PEDOT:PSS spin-coated films in the fabrication of OPVs.