Effect of excessive Pb content in the precursor solutions on the properties of the lead acetate derived CH3NH3PbI3 perovskite solar cells

Organic-inorganic CH3NH3PbI3 (MAPbI3) inverted structured perovskite films were prepared using Pb(CH3COO)2 (Pb(OAc)2) and CH3NH3I (MAI) as source materials. The structural, optical and photoelectronic properties of the MAPbI3 films varied with the Pb(OAc)2/MAI molar ratio. It was found that the Pb(OAc)2/MAI molar ratio greatly influenced the structure and morphology of the MAPbI3 films. A suitable amount of excessive Pb(OAc)2 (about 5 mol% excessive Pb) in the solution made the film smoother with improved film crystallinity. This resulted in enhanced power conversion efficiency (PCE). However, for films derived from solution with low Pb(OAc)2/MAI or high Pb(OAc)2/MAI ratio, defects such as pits or pinholes were easily formed with low crystallinity, and hence decreased the lifetime of the carriers and photoelectrical properties of the final solar cells. Using a solution with 5% excessive Pb, inverted structured CH3NH3PbI3 perovskite solar cells with PCE of nearly 14% were obtained.