Amrita Haldar

Investigation of recombination dynamics for indium tin oxide-free organic photovoltaics by illumination dependence study

Highly conductive poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is used as an anode material to construct flexible organic photovoltaics on plastic, poly(ethylene naphthalate) (PEN) substrates with a device structure of PEN/modified PEDOT:PSS/poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Al. The indium tin oxide (ITO)-free flexible device exhibits a 20% increase in power conversion efficiency under 1 sun with a higher open circuit voltage (0.67 V) compared to that of the reference device having an ITO anode on a glass substrate (0.54 V). A study of the different recombination mechanisms within these two device structures is carried out by comparing the illumination responses of open circuit voltage as well as short circuit current. The results explain the varying trend of fill factor and power conversion efficiency with respect to the light intensity and suggest that a bimolecular recombination mechanism is dominant in the ITO-free devices.