Comparison of one and two-stage growth approaches for close space sublimation deposition of Sb2Se3 thin film solar cells

In this work, we investigate the impact of grain structure and ribbon orientation on Sb2Se3 solar cells deposited by close space sublimation (CSS). Films of Sb2Se3 were produced using either a single -stage low-temperature "seed-layer" deposition, a high-temperature "growth-layer" deposition, or a combined two-stage deposition process combining both "seed" and "growth" layers. This study demonstrates the essential nature of the "seed" layer to achieve the required substrate coverage and ensure functioning Sb2Se3 solar cells by this technique. A photovoltaic efficiency of 5.07 % was obtained by fabricating solar cells with a two-stage Sb2Se3 growth process using the structure (FTO/TiO2/Sb2Se3/P3HT/Au) in superstrate configuration. Comparisons were made between device performance and ribbon orientation assessed by XRD measurements via a ribbon carrier transport (RCT) analysis method, as well as with surface coverage and grain size. The addition of a second growth stage was found to result in a more vertical ribbon orientation compared to a single low temperature deposition, however predominantly controls the overall surface coverage. We observe no obvious links between the orientation of ribbons and the cell performance. Instead we propose that the performance, and in particular the device VOC, is more strongly determined by the overall grain structure rather than simply by the ribbon orientation.