Photovoltaic parameters and stability study of HTM-free mixed-cation perovskite solar cells by incorporating additives to absorbing layers

In this study, quick route-coating is practiced to substitute methyl ammonium (MA) cation with formamidinium (FA) at different ratios. Through optimizing the MA:FA ratio, a maximum power conversion efficiency (PCE) of 8.31% is achieved for holes transporting material-free MA_0.8FA_0.2PbI₃ mixed PSCs with the J_SC of 19.02 mA/cm², V_OC of 0.859 V and FF of 50.88%. Then, to improve the performance, stability and carrier transport dynamic, various additives (PVA, PVP, PEG and EC) are incorporated into the perovskite layer. The treatment of perovskites with additives has proved to cause significant changes in the surface roughness, charge accumulation, charge transport, charge transport resistance, photovoltaic performance and cell stability. PCE of the PSCs mixed with PVA, PVP, EC and PEG optimally reaches 12.76%, 11.28%, 10.38% and 8.92%, respectively. Among the additives, EC and PVP provide better stability owing to the excellent interaction between the functional group of the additives and the perovskite. Surface modification and charge transport also occur better with those two additives.