Light soaking effect on the performance of Sb2S3 based solar cells under low light intensity

Abstract

Antimony sulphide (Sb2S3) solar cells have achieved the highest efficiency of 7.69% in practice; however, it is lower than theoretical predictions. The main drawback of Sb2S3 solar cells is the defects in the bulk, grain boundaries, and at interfaces. The light soaking effect (LSE) was observed in FTO/TiO2/Sb2S3/P3HT/carbon solar cells, which were fabricated via a modified solar cell configuration utilising a novel spin coating approach. The solar cells were then characterised to identify the reasons behind LSE because improving the stability of Sb2S3 solar cells requires the suppression of LSE. Overall, the initial measurements of these solar cells resulted in efficiency of 0.1 – 0.5%, short circuit current density (JSC) of 1 – 4 mA cm–2, open circuit voltage (VOC) of 0.1 – 0.5 V and fill factor of 0.25 – 0.30; however, with illumination, JSC enhanced while VOC decreased slightly. Even though the rate of change in JSC with illumination time was similar, it can be improved by passivating the bulk Sb2S3 layer, enhancing charge transfer, and decreasing its thickness. Additionally, when solar cells were evaluated temporarily, improvement of 4.14 – 17.65% in JSC was observed without any illumination. Therefore, it was suspected that defects in fabricated solar cells generate heat. At low intensities, solar cells demonstrated higher performance in I-V plots. When VOC versus intensity plot was elucidated, these solar cells had trap-assisted recombination at the lower intensity (≈ 20 mW cm–2) and bimolecular recombination at the higher intensity. If these recombination processes could be minimised, it would be possible to achieve better performing Sb2S3 solar cells with minimum LSE. Moreover, the major suspected locations of defects in these solar cells are found to be in the grain boundaries and interfaces of the Sb2S3 layer.