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

The polymer additive strategy provides a facile and cost-effectiveway for passivating defects and trap sites at the grain boundariesand interfaces and acting as a barrier against the external degradationfactors in perovskite-based devices. However, limited literature existsdiscussing the integration of hydrophobic and hydrophilic polymeradditives in the form of a copolymer within the perovskite films.The inherent difference in the chemical structure of these polymersand their interaction with perovskite components and the environmentleads to critical differences in the respective polymer-perovskitefilms. The current work utilizes both homopolymer and copolymer strategiesto understand the effect of polystyrene (PS) and polyethylene glycol(PEG), two common commodity polymers, over the physicochemical andelectro-optical properties of the as-fabricated devices and the distributionof polymer chains across the depth of perovskite films. The hydrophobicPS integrated perovskite devices PS-MAPbI(3), 36 PS-b-1.4-PEG-MAPbI(3), and 21.5 PS-b-20-PEG-MAPbI(3) outperform hydrophilic PEG-MAPbI(3) and pristine MAPbI(3) devices and exhibit higherphotocurrent, lower dark currents, and greater stability. A criticaldifference is also observed in the stability of devices, where rapiddecay of performance is observed in the pristine MAPbI(3) films. The deterioration in performance is highly limited for hydrophobicpolymer-MAPbI(3) films as they maintain 80% of their initialperformance.