Improving the Photovoltage of Blade-Coated MAPbI3 Perovskite Solar Cells via Surface and Grain Boundary Passivation with π-Conjugated Phenyl Boronic Acids

High-density electronic defects at the surfaces and grain boundaries (GBs) of perovskite materials are the major contributor to suppressing the power conversion efficiency (PCE) and deteriorating the long-term stability of the solar devices. Hence, the judicious selection of chemicals for the passivation of trap states has been regarded as an effective strategy to enhance and stabilize the photovoltaic performance of solar devices. Here, we systematically investigated the passivation effects of four organic π-conjugated phenylboronic acid molecules: phenylboronic acid, 2-amino phenylboronic acid (2a), 3-amino phenylboronic acid (3a), and 4-amino phenylboronic acid (4a) by adding them into the methylammonium lead iodide (MAPbI3) precursor solution. We found that solar devices with an optimized 5% (mol %) 3a treatment achieve the best passivation effect due to the strong cross-linking ability via hydrogen bonding interactions between the I of the [PbI6]4- octahedral network of perovskite films and the cross-linking terminal groups [-B(OH)2, (-NH2)] of 3a. Moreover, the lone pair of electrons on the N atom of an amino group of 3a can passivate the uncoordinated Pb2+ defects at the surface/GBs. As a result, the 3a-passivated device shows a high open-circuit voltage of 1.13 V, which is a 14.1% improvement compared to the control device (0.99 V). Moreover, the reduced defect density and improved carrier lifetimes enabled a high PCE of 18.89% in our blade-coated champion inverted structure of MAPbI3 solar cells, with improved long-term stability.