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.