Effect of Chemical Bonding Nature of Post-Treatment Materials on Photovoltaic Performance of Perovskite Solar Cells

We report here on the effect of chemical bonding nature of post-treatment materials on photovoltaic performance in perovskite solar cells using pyridinium iodide (PyI) with delocalized pi electrons and piperidinium iodide (PpI) without a pi bond. A gradual increase in power conversion efficiency (PCE) from 20.13% to 22.26% is observed as the PyI concentration increases from 0 to 40 mM, while PCE is optimized at relatively low concentration of 5 mM for PpI. It is found that a PyI layer is formed at the perovskite/HTL interface by the PyI treatment, which is beneficial for hole extraction even at increased interlayer thickness. On the other hand, an insulating 1-D PpPbI(3) formed by PpI treatment blocks charge separation, which is pronounced at high concentration. Our comprehensive comparative work on post-treatment materials delivers a message that different thicknesses for each material are required to achieve decent photovoltaic parameters.