Effect of Excess PbI₂ in Fully Printable Carbon-based Perovskite Solar Cells

Excess lead iodide (PbI₂) has been reported to improve the power conversion efficiency (PCE) in the standard perovskite solar cell (PSC) with 2,2,7,7-Tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9- spirobifluorene (spiro-OMeTAD) as a hole-transporting material. In this study, we studied the effect of having excess PbI₂ in fully printable carbon-based perovskite solar cells (PSC). Excess amounts of PbI₂, ranging from 0 % to 15 %, were added to the equimolar perovskite solution for infiltration in the carbon-based PSC architecture. There was an improvement in the average value of open-circuit voltage (0.87 to 0.91 V) with increased PbI₂, but there was no clear trend in fill factor and current density. All devices showed good stability under ambient conditions without encapsulation. The device containing 15 % excess PbI₂ showed degradation under continuous illumination, whereas there was no degradation with an equimolar ratio of perovskite precursors.