A-site tailoring in the vacancy-ordered double perovskite semiconductor Cs2SnI6 for photovoltaic application

Air-stable caesium tin iodide (Cs2SnI6) double perovskite are highly desirable for substituting the lead-based halide perovskite solar cells. In this work, we have investigated the effect of A-site tailoring in Cs2SnI6 by adding monovalent cation (Rb and Ag) on film growth properties, (morphology, structural properties, opto-physical properties), optoelectronic properties, and device characteristics. The crystal analysis suggests that the A-site additives suppress CsI secondary phase in (Cs1-xAx)2SnI6 film for x 0.5 whereas multiple secondary phases occur in higher additive content. The opto-physical properties reveal a small change in bandgap energy for alloyed film and excellent thermal stability in ambient air. The inverted device structure ITO/CuI/Cs2SnI6-alloyed/PCBM/AZO/Ag, for the first time, demonstrated the improvement in device parameters (with VOC~ 0.38 V and efficiency of ~0.66%) for the alloyed films. The capacitance analysis reveals that the high defect density in bulk as well as at the interface (Nt > 1019 cm−3) has a deleterious effect on the device performance. In this work, we underline insight into the A-site tailoring of Cs2SnI6 double perovskite and the dominant limiting factors for getting high device performance.