Comparison between PLD and R2R sputtering with the identification between deposition technique, sheet resistance and AVT of the TCO

Deliverable 5.8 encompass the development of transparent conductive oxides (TCO) for the CITYSOLAR organic and perovskite solar cells, and in particular the comparison between TCOs developed from pulsed laser deposition (PLD) and Roll-to-Roll (R2R) reactive sputtering processes. The individual solar cells in the tandem stack have requirements for high Average Visible Transmittance (AVT, 50% for the final tandem device), and at the same time strong light absorption in the region where the solar cells convert light into electrical energy. The AVT encompass contributions from absorption in the active layer in the solar cells, and also parasitic absorption from transport layers and transparent electrodes, which may lead to non-neglicible absorption loss. To minimize unwanted absorption losses, the aim of this deliverable was to develop and compare transparent conductive oxides from R2R sputtering and PLD process, which can be integrated in the CITYSOLAR tandem cells. We report here on the development of transparent conductive oxides from aluminium doped Zin Oxide (AZO), and demonstrate that optimized AZO possess low sheet resistance of 14 ohm/sq and 35 ohm/sq, when developed from R2R sputtering and pulsed laser deposition, respectively. High optical transmittance above 80% is observed for both types of AZO, which can go as high as 95% at 550nm, with substrate loss subtracted. Furthermore, Indium Tin Oxide (ITO) with low sheet resistance of 16-20 ohm/sq has also been developed from pulsed laser deposition. The AZO has been developed from R2R processes, and integration into OPV cells demonstrated. We emphasize that for both pulsed laser deposition and reactive sputtering, solutions that are based on fully on ITO-free materials, i.e. avoiding rare Indium typically used in TCOs, have been demonstrated. Hence, we focus on using low cost, abundant and non toxic material systems, which makes them interesting from both commercial and improved sustainability aspects.