Synergetic Effects of Recombination-blocking, Band-bending and Gap-state Manipulation by Interfacial Engineering in solid-state DSSCs comprising Cs2SnI6 electrolyte

Here, we report the first work relating to interface-modification to solid state dye sensitized solar cells (ss-DSSCs) with Cs2SnI6 electrolyte by introducing KI or guanidine thiocyanate (GuSCN). Results show that KI and GuSCN modifications endow VOC improvements of 35% and 31% respectively, leading to power conversion efficiency (PCE) of 5.89% and 5.64%. Although both KI and GuSCN modification can retard charge recombination, their VOC improvement mechanism is not exactly the same: KI based devices mainly enjoy up-bending of the conducting band of TiO2 and the down shift of the gap states in Cs2SnI6, while the VOC improvement in GuSCN devices is dominated by the lowering of gap states in Cs2SnI6. Structural analysis indicates that KI/GuSCN modification causes CsSnI3 impurity and disrupts Cs2SnI6 growth at the interface, while the bulk Cs2SnI6 is uninfluenced, e.g., consisting cubic Cs2SnI6 particles with good crystalline. Our work provides insights for VOC improvement in ss-DSSC with interface modification in terms of electronic and material structural aspects, which enrich property-material/interface structure relationship, beneficial to both ss-DSSC architecture and material engineering.