Defect passivation and morphology engineering via polyethylene glycol additive for high-performance FAPbI3 perovskite photodetectors

Perovskite photodetectors have attracted considerable attention due to their excellent optoelectronic properties and low-cost solution processability. However, the practical application of formamidinium lead iodide (CH(NH 2 ) 2 PbI 3 , FAPbI 3 ) based devices is severely hindered by high defect densities, phase instability, and non-radiative recombination losses. Herein, we demonstrate a simple and effective strategy to simultaneously address these challenges by incorporating polyethylene glycol (PEG) as a multifunctional additive into the FAPbI 3 precursor solution. Systematic optimization reveals that an optimal PEG concentration (2 mg/mL) significantly improves film crystallinity, enlarges grain size and reduces trap density, as evidenced by XRD, SEM, and SCLC analyses. The synergistic interaction mechanism was investigated by combining XPS and FTIR spectroscopy. Consequently, the optimized PEG-2 photodetector exhibits a ∼30% reduction in dark current, a ∼750% enhancement in photocurrent, and a ∼13-fold increase in on/off ratio compared to the pristine device. Both responsivity and detectivity are substantially improved across the visible spectrum, achieving a responsivity of 3.8 mA/W and a specific detectivity of 9.76 × $\times$ 10 10 Jones. This work establishes PEG as a low-cost, multifunctional additive for defect passivation and morphology control in FAPbI 3 perovskites, offering a simple strategy toward high-performance, stable photodetectors and molecular guidance for rational polymer design.