Photovoltage Approaching 0.9 V for Planar Heterojunction Silver Bismuth Iodide Solar Cells with Li-TFSI Additive

Silver bismuth iodide (Ag-Bi-I) as an environmentally friendly semiconductor with suitable band gap and high stability has been regarded as a potential photovoltaic material, while the reported mesoscopic devices all showed poor open circuit voltage (V-oc) of 0.5-0.6 V. Here, we successfully fabricated AgBiI4 planar heterojunction solar cells via a solution method with a Voc approaching 0.9 V, in which 2 wt % lithium bis(trifluoromethylsulfonyl)-imide (Li-TFSI) was added into the AgI:BiI3 precursor. The device presents a power conversion efficiency of 2.50 +/- 0.20% with a V-oc of 0.82 +/- 0.20 V. Experimental results indicated that the readily coordinated component in the organic salt, TFSI-, could assist film growth and result in a full coverage morphology. Furthermore, double layer devices showed the carrier separation occurred in the interface of SnO2/AgBiI4. These results indicated interface extraction and film enhancement should be concerned in further improvements.