Active-layer evolution and efficiency improvement of (CH3NH3 3Bi2I9-based solar cell on TiO2-deposited ITO substrate

We systematically investigated the development of film morphology and crystallinity of methyl-ammonium bismuth (III) iodide (MA 3 Bi 2 I 9 ) through onestep spin-coating on TiO 2 -deposited indium tin oxide (ITO)/glass. The precursor solution concentration and substrate structure have been demonstrated to be critically important in the active-layer evolution of the MA 3 Bi 2 I 9 -based solar cell. This work successfully improved the cell efficiency to 0.42% (average: 0.38%) with the mesoscopic architecture of ITO/compact-TiO 2 /mesoscopic-TiO 2 (meso-TiO 2 )/MA 3 Bi 2 I 9 /2,2′,7,7′-tetrakis(N,N-di-4-methoxyphenylamino)-9,9′spiro-bifluorene (spiro-MeOTAD)/MoO 3 /Ag under a precursor concentration of 0.45 M, which provided the probability of further improving the efficiency of the Bi 3+ -based lead-free organic–inorganic hybrid solar cells.