The choice of electrode for organic photovoltaics is known to be of importance to both device stability and performance, especially regarding the open-circuit voltage ($V_{\mathrm{OC}}$). Here we show that the work function of a nickel oxide anode, varied using an ${\mathrm{O}}_2$ plasma treatment, has a considerable influence on the open-circuit voltage $V_{\mathrm{OC}}$ of an organic solar cell. We probe recombination in the devices using transient photovoltage and charge extraction to determine the lifetime as a function of charge-carrier concentration and compare the experimental results with numerical drift-diffusion simulations. This combination of experiment and simulations allows us to conclude that the variations in $V_{\mathrm{OC}}$ are due to a change in surface recombination, localized at the NiO anode, although only a small change in carrier lifetime is observed.

• Received 21 May 2015

DOI:https://doi.org/10.1103/PhysRevApplied.4.024020

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© 2015 American Physical Society