Fabrication of lead-free CsBi3I10 based compact perovskite thin films by employing solvent engineering and anti-solvent treatment techniques: an efficient photo-conversion efficiency up to 740 nm

Bismuth based perovskites are emerging as a candidate for photovoltaic applications due to their low-toxicity, high structural stability, and suitable applications in photovoltaic applications. Here in this work, bismuth halide perovskite films with the stoichiometric composition of ABi3I10 (A = Cs, FA and MA) are synthesized by a one step solution process. By optimizing the appropriate anti-solvent dripping techniques, the surface morphology and optical properties of these perovskite thin films have been improved. Among the synthesized materials, CsBi3I10 perovskite showed extended absorption up to 700 nm and the bandgap was reduced to 1.75 eV. An inverted planar perovskite solar cell (PSC) employing the CsBi3I10 as an absorber layer was fabricated which showed a maximum power conversion efficiency of 0.63%. In addition, the fabricated PSC exhibited a red-shifted incident photon to current conversion efficiency (IPCE) up to 740 nm, which is higher than those of the existing bismuth-based PSCs. This improvement in the IPCE shows the potential of CsBi3I10 as an absorber for Pb-free PSCs.