Lead-free perovskite solar cells using Sb and Bi-based A 3 B 2 X 9 and A 3 BX 6 crystals with normal and inverse cell structures.

Research of CH3 NH3 PbI3 perovskite solar cells had significant attention as the candidate of new future energy. Due to the toxicity, however, lead (Pb) free photon harvesting layer should be discovered to replace the present CH3 NH3 PbI3 perovskite. In place of lead, we have tried antimony (Sb) and bismuth (Bi) with organic and metal monovalent cations (CH3 NH3 + , Ag+ and Cu+ ). Therefore, in this work, lead-free photo-absorber layers of (CH3 NH3 )3 Bi2 I9 , (CH3 NH3 )3 Sb2 I9 , (CH3 NH3 )3 SbBiI9 , Ag3 BiI6 , Ag3 BiI3 (SCN)3 and Cu3 BiI6 were processed by solution deposition way to be solar cells. About the structure of solar cells, we have compared the normal (n-i-p: TiO2 -perovskite-spiro OMeTAD) and inverted (p-i-n: NiO-perovskite-PCBM) structures. The normal (n-i-p)-structured solar cells performed better conversion efficiencies, basically. But, these environmental friendly photon absorber layers showed the uneven surface morphology with a particular grow pattern depend on the substrate (TiO2 or NiO). We have considered that the unevenness of surface morphology can deteriorate the photovoltaic performance and can hinder future prospect of these lead-free photon harvesting layers. However, we found new interesting finding about the progress of devices by the interface of NiO/Sb3+ and TiO2 /Cu3 BiI6 , which should be addressed in the future study.