Room-temperature ITO electrodes evaluated for organic solar cells using a photonic flux density figure of merit

Abstract

The performance of ITO films grown by RF sputtering as a transparent conductive oxide (TCO) was evaluated using a photonic flux density figure of merit. This figure of merit provides additional information compared to other figures of merit, since it includes in its analysis the performance along the electromagnetic spectrum comprehended between the TCO bandgap energy and the absorber bandgap energy. The ITO thin films were grown by 200 W power RF sputtering without any substrate heating or post annealing treatment varying the Ar pressure. Instead of heating, the relatively high RF power provided the energy needed to enhance the diffusion process of the sputtered species in the substrate, thus improving crystallinity. Transmittances greater than 85% were obtained in the visible region of the spectrum independently of the argon pressure used. Regarding the electrical resistivity, an average value of 10⁻³ Ω cm was obtained at 300 K. Photocurrent losses were calculated in order to compare the grown ITO films performance with an ideal one. The photonic flux density figure of merit obtained in this work suggests that the overall performance is sufficient to be implemented as TCOs in many applications; moreover, the lack of substrate heating or post-annealing treatment makes these films good candidates to be used as TCOs in heat sensitive devices such as P3HT:PCBM.