Influence of Surface Recombination on Charge-Carrier Kinetics in Organic Bulk Heterojunction Solar Cells with Nickel Oxide Interlayers

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-OC). Here we show that the work function of a nickel oxide anode, varied using an O-2 plasma treatment, has a considerable influence on the open-circuit voltage V-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-OC are due to a change in surface recombination, localized at the NiO anode, although only a small change in carrier lifetime is observed.