Hydrophobic-Hydrophilic Block Copolymer Mediated Tuning of Halide Perovskite Photosensitive Device Stability and Efficiency.

The polymer additive strategy provides a facile and cost-effective way for passivating defects and trap sites at the grain boundaries and interfaces and acting as a barrier against the external degradation factors in perovskite-based devices. However, limited literature exists discussing the integration of hydrophobic and hydrophilic polymer additives in the form of a copolymer within the perovskite films. The inherent difference in the chemical structure of these polymers and their interaction with perovskite components and the environment leads to critical differences in the respective polymer-perovskite films. The current work utilizes both homopolymer and copolymer strategies to understand the effect of polystyrene (PS) and polyethylene glycol (PEG), two common commodity polymers, over the physicochemical and electro-optical properties of the as-fabricated devices and the distribution of polymer chains across the depth of perovskite films. The hydrophobic PS integrated perovskite devices PS-MAPbI, 36 PS--1.4-PEG-MAPbI, and 21.5 PS--20-PEG-MAPbI outperform hydrophilic PEG-MAPbI and pristine MAPbI devices and exhibit higher photocurrent, lower dark currents, and greater stability. A critical difference is also observed in the stability of devices, where rapid decay of performance is observed in the pristine MAPbI films. The deterioration in performance is highly limited for hydrophobic polymer-MAPbI films as they maintain 80% of their initial performance.