Brominated zinc porphyrin assisted grain boundary defects passivation in carbon-based planar perovskite solar cells

Despite the great promotion of perovskite solar cells, the presence of defect trap states at the surfaces and grain boundaries has a negative influence on photovoltaic functionality, primarily due to the polycrystalline nature of perovskite film formation. Motivated by porphyrin molecules excellent charge mobility and various optical transitions in the visible region, we introduce a simple zinc(II)β-tetra-bromo-meso-tetra-phenyl-porphyrin as an additive in the perovskite layer to improve the performance and stability of planar perovskite solar cells. The modified electron density distribution of the molecule developed on electronegative Br sites enables the passivation of charged defect states. Its compatible energy levels and high charge mobility lead to better electron-hole transport through the perovskite layer and defect passivation in the grain boundaries. Moreover, it also has a positive effect on the perovskite film formation quality. As a result, the efficiency of the best device is up to 18.5 %, a factor of 15 % increase to that of the reference cell with a value of 16.1 %, which is superior in planar device structure with copper indium disulfide (CIS) as a hole transport material and carbon as back contact. Furthermore, enhanced hydrophobicity and crystalline quality improve the stability of devices, and the modified device maintained 96 % of its initial efficiency after 40 days in comparison with the control device with 38 % drop in its performance. [Display omitted] •A simple structure of porphyrin significantly enhances performance and stability of perovskite solar cell.•Zn-porphyrin places in grain boundaries passivates Pb2+ deep trap states.•Saddle-shaped structure of Zn-porphyrin could enhance the perovskite film uniformity.•Porphyrin provides a desired band gap alignment between perovskite and HTL.•Efficient charge extraction and grain boundaries defect passivation hinder energy losses.•An average of 14.9 % increase in efficiency is achieved by incorporating ZnTPPBr4 as an additive in perovskite layer.