A PbICl seed layer for obtaining efficient planar-heterojunction perovskite solar cells via an interdiffusion process.

Despite the previous reports on the fabrication of CHNHPbICl films via sequential deposition, the positioning and formation of PbI in MAPbICl perovskite films made from the seed layer containing PbI and PbCl in different ratios have not yet been addressed. In this study, the PbI content in a perovskite absorber layer is controlled by changing the PbCl ratio in a PbICl seed layer. The addition of PbCl in the seed layer facilitates PbI generation and affects the morphology of the perovskite film. By integrating a perovskite absorber via the PbICl seed-layer into a solar cell, we investigated the effects of the correlation between the chlorine and PbI contents on the device performance through intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. Elemental depth profiling analyses confirm that not only was the formed PbI preferentially located near the metal-oxide layer, but residual chlorine was adsorbed at the TiO layer. Our findings demonstrate that the geometric features of the formed PbI affected the perovskite solar cells according to the chlorine content, likely because of the elemental gradient induced by annealing. The PbICl-derived planar-heterojunction perovskite solar cells exhibited maximum power-conversion efficiencies of 17.56% at reverse scan and 17.21% at forward scan, suppressed current density-voltage hysteresis, and good performance distributions.